Appendix C - Positive Guidance Toolkit · 2008-10-06 · Positive Guidance is provided when that...

OntarioTrafficManual

July 2001

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1C

Introduction to theOntario Traffic Manual Appendix C - Positive Guidance Toolkit

Bo

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1COntarioTrafficManual

July 2001

Introduction to theOntario Traffic Manual Appendix C - Positive Guidance Toolkit

ISBN 0-7794-1859-X

Copyright © 2001Queen’s Printer for Ontario

All rights reserved.

Ontario Traffic Manual • July 2001 1

Book 1, Appendix C • Positive Guidance Toolkit

Table of Contents

1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5

2. Principles . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6

2.1 Definition and Concept . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6

Control, Guidance and Navigation Levels of Performance . . . . . . . . . . . . . . . . . . . . . . . . 6

Task Complexity . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7

Primacy . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7

Information Handling . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7

Perception-reaction Time (PRT) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8

2.2 Driver Expectancies and Surprises . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8

Roadway Design . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8

Traffic Control Devices . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11

2.3 Key Considerations . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12

2.4 Failures at the Guidance Level . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 13

2.5 Information at the Guidance Level . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 13

Roadway Environment . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 13

Traffic Control Devices . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 13

Traffic . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 14

2.6 Hazards at the Guidance Level . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 14

Fixed Objects . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 14

Moving Objects . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 14

Highway Conditions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 14

Situations . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 15

Strategic Improvements . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 15

2.7 Drivers Avoiding Hazards . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 15

Detecting the Hazard . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 15

Ontario Traffic Manual • July 20012


Recognizing the Hazard . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 16

Deciding What to Do . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 16

Doing It . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 16

2.8 Planning, Design and Construction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 16

3. Procedures . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 17

3.1 Project Planning and Data Collection . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 18

Data Collection and Office Review . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 18

Assembly of Existing Site Information . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 19

Initial Condition Diagram . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 19

Collision Diagram/Accident Summary . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 19

List of Things to Look For and At . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 19

Project File . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 19

Site Survey and Operations Review . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 19

Informal Field Data Collection . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 20

Drive-through . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 20

Commentary Drive-through . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 20

Walk-through . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 20

Site Survey . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 20

Operations Review . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 20

Performance Data Collection . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 20

Data Collection Plan . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 21

Applicable Data to Collect . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 21

3.2 Applying the Positive Guidance Procedure . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 25

Identifying the Hazards . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 25

Identification of Hazards and Inefficiencies . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 25

Fixed Objects . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 25

Moving Objects . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 26

Highway Conditions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 26

Situation Hazards . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 26

Inefficient Operations . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 26

Determination of Significant Hazard Clusters . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 28

Assessing Hazard Visibility . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 31

Determining Land Use and Hazard Avoidance Manoeuvre . . . . . . . . . . . . . . . . . . . . . . . 31

Specify Applicable Sight Distance Case . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 31

Determine Approach Speed . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 31



Determine Stopping and Decision Sight Distance . . . . . . . . . . . . . . . . . . . . . . . . . . 31

Specifying Information Handling Zones . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 32

Rating Hazard Visibility . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 33

Determining Expectancy Violations . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 35

General Expectancy Review . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 35

Detailed Expectancy Violation Determination . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 39

Information Load Analysis . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 39

Information Load Factors . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 40

Individual Factor Ratings . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 40

Overall Site Ratings . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 40

Information Load . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 40

Specifying Information Needs . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 42

Evaluating the Current Information System . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 44

Presence . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 44

Location . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 44

OTM Compliance . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 44

Expectancy Violations . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 44

Superfluous Displays . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 44

Field of View . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 44

Target Value . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 44

Content . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 44

Accuracy . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 46

Understandability . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 46

Ambiguity . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 46

Legibility . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 46

Developing Improvements . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 46

Historical Effectiveness . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 46

Human Factors Considerations . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 47

Target Populations . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 47

OTM Effectiveness Criteria . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 47

Standardization . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 47

Engineering/Economic Considerations . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 47

Information Display Techniques . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 47

4. Case Studies . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 48

4.1 Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 48



4.2 General Procedures . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 48

Diagnosis of Deficiencies . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 49

Development of Countermeasures . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 49

Recommendations and Conclusions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 49

4.3 Urban Intersection Case Study . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 49

Site Location . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 49

List of Tables

Table 1 – Traffic Performance Measures . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 22

Table 2 – Fixed Object Hazards . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 25

Table 3 – Moving Object Hazards . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 26

Table 4 – Highway and Traffic Condition Hazards . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 27

Table 5 – Sight Distance Case . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 31

Table 6 – Stopping and Decision Sight Distance Values . . . . . . . . . . . . . . . . . . . . . . . . . . 32

Table 7 – General Expectancy Review Factors . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 36

Table 8 – First-of-a-kind Features . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 39

Table 9 – Standard Information Needs by Zones . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 42

List of Figures

Figure 1 – Allen Road Symbol Sign . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9

Figure 2 – Allen Road Diagrammatic Sign . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9

Figure 3 – Tangential Roadway at Curve . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10

Figure 4 – Double Exit Lane Drop . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10

Figure 5 – Split with Off-route Movement to the Left . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11

Figure 6 – Optional Lane Split . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11

Figure 7 – Hazard Profile . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 28

Figure 8 – Information Handling Zones . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 33

Checklists

Checklist 1 – Hazard Identification . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 29

Checklist 2 – Hazard Visibility Assessment . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 34

Checklist 3 – Expectancy Violation Determination . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 37

Checklist 4 – Information Load Analysis . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 41

Checklist 5 – Information Needs Specification . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 43

Checklist 6 – Current Information System Evaluation . . . . . . . . . . . . . . . . . . . . . . . . . . . . 45




1. Introduction1

In late 1972, a narrow bridge accident in rural NewMexico took the lives of several Texas children andaccompanying adults on a school outing. Thattragedy was the genesis of the Positive Guidanceprogram. The program was undertaken by theFederal Highway Administration (FHWA) to improvesafety at hazardous locations. In testimony beforethe U.S. Congress, the Federal HighwayAdministrator, Norbert Tiemann stated, “If wecannot physically protect motorists, then we have anobligation to provide motorists with information toprotect themselves.” Positive Guidance wasidentified as the means by which that obligationwould be met.

In 1977, FHWA published the first Users Guide toPositive Guidance, and began conducting trainingsessions in the United States. In 1986, PositiveGuidance was brought to Canada for the first time,at a seminar at the University of Calgary. Seminarsand workshops on Positive Guidance were heldthroughout Ontario under the sponsorship of theMinistry of Transportation (MTO) and by the OntarioTraffic Conference beginning in 1988. In the midand late 1980s, there was a growing awareness

within the MTO of the role of human factors orergonomics in providing a safe, efficient drivingenvironment for the broad range of Ontariomotorists capabilities and limitations. Trainingsessions relating to understanding the needs of thegrowing elderly population, and projects related tothe French Language Services Act were conductedby human factors professionals as consultants orunder contract to MTO.

This appendix to the Ontario Traffic Manualdocuments both the principles upon which PositiveGuidance is based and a simplified procedure bywhich engineers and technicians can identify andanalyze driver problems at hazardous locations andblack spots in order to provide appropriatesafety-related information.


1 The Positive Guidance Toolkit was prepared by Gerson J. Alexander, Positive Guidance Applications, Inc., 6102 Neilwood Drive, RockvilleMD 20852, USA; email: [email protected], and Harold Lunenfeld, Federal Highway Administration, U.S. Department of Transportation.

© Copyright by Positive Guidance Applications, Inc. Permission is expressly granted to the Ontario Ministry of Transportation for anyuse within its purview. Permission is further granted to quote excerpts with customary attribution. Permission to reproduce or republishany substantial portion of text or Checklists or Tables or Figures must come from Mr. Alexander.



2. Principles

Positive Guidance means giving drivers theinformation they need to avoid hazards, when andwhere they need it, in a form they can best use it.Since positive guidance can be achieved onlythrough the understanding and integration ofergonomics (human factors) and highwayengineering technologies, some basic humanfactors principles are included in Section 2 of thisAppendix.

In terms of driver behaviour, optimum highwaydesign is achieved where drivers know what toexpect from the highway, where their attention isnaturally attracted to the most important sources ofinformation, and they have adequate time torespond to conditions and situations as they arise.To achieve this objective, it should be evident that allelements of highway planning, design, construction,maintenance and operations consider expectancyand primacy.

2.1 Definition and Concept

Any information carrier, including the highway,which helps or directs drivers in making speed and/or path decisions transmits guidance information.Positive Guidance is provided when that informationis presented unequivocally, unambiguously andconspicuously enough to meet decision sightdistance criteria and enhances the probability ofdrivers making appropriate speed and pathdecisions.

Control, Guidance andNavigation Levels of Performance

Control refers to task performance related to adriver’s interaction with the vehicle. Vehicles arecontrolled in terms of speed, path and direction.Drivers exercise control through the steering wheel,accelerator and brake. Information about how welldrivers perform at the control level comes from thevehicle and its displays as well as visual observationof changes in speed, path and direction. Driversreceive continual feedback through vehicle responseto various control manipulations. Overt response tohazards is part of the control level of performance.

Guidance refers to task performance related to adriver’s picking out and maintaining a safe speedand path. Control subtasks require action by thedriver. Guidance requires decisions involvingjudgements, estimates and predictions. The drivershould evaluate the immediate environment andtranslate changes in alignment, grade and trafficinto control actions needed to stay in theappropriate lane at an appropriate speed for theprevailing conditions. Information at this level comesfrom the highway – its alignment and grade,geometric features, hazards, shoulders, etc.; fromtraffic – speed, relative position, gaps, headway, etc.;and traffic control devices – regulatory and warningsigns, signals and markings.

Navigation refers to the activities involved inplanning and executing a trip from origin todestination. Drivers generally evaluate routenumbers and/or names, interchange or intersectiondesignations, cardinal directions and landmarks.They make guidance level decisions at choicepoints, and ultimately translate those decisions intocontrol actions. Off-line information sources includemaps, verbal directions and prior experience. On-lineinformation input comes from the full range ofguide signs, verbal directions and landmarks.Depending on the rate of implementation ofIntelligent Transportation Systems (ITS), map



information might be increasingly presented on-linein the vehicle. This might create additionalinformation processing concerns.

Task Complexity

Information and task performance associated withthe three levels of performance, control, guidanceand navigation form a hierarchy of complexity. Atcontrol, the lowest level, information processing andvehicle handling is relatively simple, and socompletely over learned by experienced drivers, thatit is performed almost without conscious thought.At the guidance and navigation levels, informationhandling is often increasingly complex anddemanding, and drivers need more processing timeto make decisions and respond to informationinputs. This frequently occurs in urban locations, atintersections and interchanges and where there isheavy traffic demand. The nature and number ofhazards and of the available information displaysalso affect task complexity. The scale of complexityincreases from control through navigation.

Primacy

It should be evident that at any given location on thehighway, some information is more important thanother information. Primacy refers to the relativeimportance of each level of the driving task, and ofthe information associated with a particular activitywithin each level. Here too, there is a hierarchicalscale. The major criterion upon which primacy isassessed is the consequence of driver performanceerror. Since loss of vehicle control is of the greatestimmediate concern to the driver, and the results ofwhich can be catastrophic, the control level isassigned the highest primacy. A guidance levelfailure also is assigned a high primacy in that errorsin speed and path selection frequently result inaccidents. In navigation, where errors usually result

in delayed, lost or confused motorists, the lowestprimacy is assigned. The scale of primacy decreasesfrom control through navigation.

Primacy is a most important consideration wheninformation competes for drivers’ attention. If thereis inadequate time to process all the information atone location, high primacy needs should be satisfiedfirst and lower primacy needs should be deferred.Information should be so placed as to spread theinformation challenge at locations where criticaldriver actions are required.

Information Handling

While driving, drivers do many thingssimultaneously or nearly so. They monitor traffic,follow the road, stay in a lane, read signs, listen tothe radio, and accelerate and decelerate theirvehicles. At any given point in time, drivers mighthave several overlapping needs associated witheach level of performance. To handle this array ofneeded and available information, drivers mustsearch the environment for information sources,detect their presence, recognize their relevance andmake decisions to perform control actions safelyand efficiently. Thus, information should be availablewhen and where needed, and in a form best suitedfor its intended purpose.

Drivers receive and handle information using asignal search, detection, recognition and useprocess. In the search and detection modes, driversscan the environment and sample the information inshort glances until a potentially needed source isdetected. Once detected, the source is attended toeither continuously or intermittently until recognized.Drivers then decide if the information is needed. Ifneeded, it is processed and used to make speed,path and direction decisions and control actions. Insituations where information competes for drivers’attention, unneeded and low primacy information is



shed. Errors could occur when drivers process lessimportant information and miss or shed moreimportant information.

Relevant information that is not immediately used isstored in short-term memory. Information that is sostored is quickly forgotten (sometimes called loadshedding) if not used or reinforced soon. Whenreinforced by repetition, information is moved tolong-term memory for future use.

Perception-reaction Time (PRT)

PRT includes the components of informationprocessing; detection, recognition, decision makingplus action initiation. It varies not only fromindividual to individual, but also as a function ofdecision complexity, information content and driverexpectancy. The more complex the decision, or themore information needed to make a decision, thelonger the PRT. Clearly, long PRTs reduce the timeavailable to load shed, attend to other informationsources and to respond to other task requirements,increasing the probability of error. Although 2.5seconds is the constant used for PRT in design andsight distance calculations, it is hardly a constant.Even for something as simple as brake reactiontime, the literature shows substantial ranges in PRT(from less than one second to more than fourseconds), with the range of responses tounexpected signals higher than the range ofresponses to expected signals. PRT at night will belonger than daytime for the same informationcontent; quite a bit longer if the source of theinformation is neither illuminated nor reflectorized.Similarly, information detected in peripheral visionwill also result in longer PRT.

2.2 Driver Expectancies and Surprises

The nature of the driving task and drivers’information handling characteristics emphasize theimportance of expectancies. Reaction to anunexpected event takes longer than when the eventis expected. Conversely, drivers are less likely tobecome confused or commit errors when theirexpectancies are reinforced. Because the key tosafe, efficient driving task performance is rapid,error free information handling, what drivers expectand do not expect has a major influence on taskperformance, particularly under time pressures andhigh task loading.

Expectancy relates to a driver’s readiness to respondto conditions, situations, events and informationsuccessfully. It influences the speed and accuracy ofinformation processing, and is one of the moreimportant driver related characteristics in the designand operation of highways. Configurations,geometric features, traffic operations and trafficcontrol devices that meet or reinforce expectancieshelp drivers to respond quickly, efficiently andwithout error. The following section describes theexpectancy principle with some Ontario examples.

Roadway Design

The interchange configuration on the outer lanes ofwestbound Highway 401 and Allen Road is a goodexample of an unusual design configuration thatmight contribute to driver expectancy problems.Because almost all exits are on the right, unfamiliarmotorists expect to exit from the right lane of thefreeway. Without conspicuous, specific advancenotice, unfamiliar westbound motorists wanting toexit to Allen Road are likely to move to the right.Here, motorists will either miss their exit or performan erratic late lane change to get to it. Even moreunusual is the fact that it is a double expectancyviolation – the left exiting movement is tangential tothe approaching mainline roadway.



Freeway tangential exit ramps create expectancyproblems for drivers. Interchange exits with thisconfiguration are the scenes of many unintentionalerratic manoeuvre and other errors. Drivers findthemselves leaving the freeway by going straightahead on the tangent while the freeway curves tothe right or left. The tangential off movement is thusboth an unexpected feature and one that createsperceptual problems whether the tangential exitingmovement is at the beginning of the curve orwithin it.

Figure 1 – Allen Road Symbol Sign

Because

tangential exiting movements have the effect ofpulling motorists in the adjacent through lane off themainline onto the exiting ramp, more drivers areaffected, interactions in the traffic stream are moreturbulent, and the potential for driver error is greater.Wherever left exits have been located, whether aloneor in combination with another expectancy violation,like a lane drop or a tangential exiting movement,from Toronto to Vancouver, they have been recognizedas sources of operational problems. Contributing to adriver orientation problem at this exit is anincompatibility between two signs in advance of theexiting movement. As shown in Figure 1, the first

sign, mounted overhead is the symbol sign for the leftexit. It shows the freeway going straight and theexiting movement curving to the left.

The following diagrammatic sign, shown in Figure 2depicts the actual configuration – the freeway curvingto the right and the left exiting movement goingstraight. It even shows the left lane is optional. Driversmight stay in that lane to exit or to continue on theHighway 401. Making the situation even moredifficult is the fact that a downgrade and the everpresent heavy Highway 401 traffic hides visibility ofthe actual configuration.

Figure 2 – Allen Road Diagrammatic Sign

In general, no traffic control device has yet beenfound that can adequately warn drivers abouttangential exit ramps, Tangential exit ramps are besttreated by so configuring the diverge area that theoff movement does not appear as the continuation ofthe main roadway. If the diverge area could berelocated as little as 30 m up or downstream of thecurve or the divergence angle is no longer tangentto the curve, so that drivers would be required tomake a steering adjustment to exit, the desiredeffect could be achieved.



There are rural two-lane road situations that functionsimilarly to the freeway tangential exit ramp. Off-roadfeatures, such as a line of trees or railroad tracks thatrun parallel and adjacent to the highway createdrivers’ expectancy that the condition will continue.Another similar situation is that of a tangent roadwayintersecting at the point of curve of a turningroadway, as shown in Figure 3 taken at theintersection of Provincial Highway 3, which is MainStreet West and Regional Road 5, Killaly Street Weston the west side of the City of Port Colborne.

Figure 3 – Tangential Roadway at Curve

Figure 4 shows the double exit lane drop sign atBathurst Street on the outer lanes of Highway 401.At most freeway exits, and particularly on Highway401, motorists must move into a deceleration laneor choose the adjacent optional lane to exit thefacility. It is therefore an expectancy violation whena lane that had been a through lane exits the facilitydirectly, leaving no option. Instead of having tochange lanes to leave the freeway, motorists arerequired to change lanes to stay on the freeway. Theblack-on-yellow “EXIT/SORTIE” panel has theneeded conspicuity when placed on the white-on-blue guide sign to gain drivers’ attention. Theuniform application of the panel at interchange lanedrops serves to structure the appropriateexpectancy. It is interesting to note that the distance

between the gore at Bathurst Street and the gore atAllen Road is less than 300 m. It can be anticipatedthat unfamiliar motorists will have difficulty guidingthemselves through the configuration of both theseunusual interchange designs.

Figure 4 – Double Exit Lane Drop

A common freeway design feature with the potentialfor violating expectancies is a variant of theinterchange lane drop – the split or bifurcation. Twokinds of split surprise drivers: first, any split wherethe off-route movement is to the left of the throughroute movement, as shown in Figure 5 takeneastbound on the QEW at the Highway 405interchange; and second, the optional lane split, asshown in Figure 6 taken on westbound QEW at theHighway 403 interchange.



Figure 5 – Split with Off-routeMovement to the Left

The optional lane split creates expectancy problemsfor many drivers. Because it is a lane drop, drivers inthe exiting lane(s) are affected. Additionally, driversin the optional lane do not expect to be faced with alane choice by staying in lane. This situation couldbe described as a classical dilemma – the choicebetween equal alternatives. When drivers make alate choice, or worse – no choice, somethingundesirable usually happens, such as an erraticmanoeuvre, a gore crossover, a fixed object struck inthe gore, a truck jackknife, etc.

Any reduction in width of the road represents anexpectancy violation and a hazard to drivers.Situations such as main line lane drops, work zonesand narrow bridges are common sources ofpavement width reduction. While all are expectancyviolations, narrow bridges are particularly difficultbecause of the many configurations they take.Narrow bridges come in a variety of shapes and sizes,from those that are short box culverts to long bridgeswith trusses. Their narrowness ranges from loss ofshoulder to narrowing of a lane width to a one-lanebridge that handles two-way traffic. Narrow bridgesoccur on curves (both horizontal and vertical), and indips, making them hard to see. Thus, they are notonly unexpected, they might be hard to detect,

recognize and negotiate in the presence of oncomingtraffic. Conspicuous advance warning is one key toproviding safety.

Figure 6 – Optional Lane Split

Traffic Control Devices

Traffic control devices serve to structure expectanciesabout downstream features and operations. They alsostructure expectancies about information treatmentsat similar locations. The key to effective expectancystructuring is uniformity and standardization.Standard devices inconsistently applied createexpectancy problems for drivers. If upstream curvewarning signs underestimate maximum safe speed,drivers will expect similar underestimation for similarcurves downstream. When a downstream curve ismore realistically signed, drivers might be unpreparedor unable to respond properly. Traffic control devicesnot only serve to structure expectancies, they tend toviolate expectancies if misapplied, inconsistentlyapplied, are absent when needed, present whenunneeded, and/or ambiguous.



Traffic signals often violate expectancies. At manysignalized intersections, motorists who are stoppedfor the red can see the signal display for thecrossing roadway. This is particularly true atintersections where the roadways cross at somethingother than a 90 degree angle. From the stoppedposition, the lenses on the signal face for the crossingmovement are frequently clearly visible. Invariably, anon-local driver at the head of the queue will moveinto the intersection when the crossroad signalchanges from amber to red, expecting to get thegreen. But all too frequently their signal indicationdoes not get the green. Lagging greens, protectedturning movements, pedestrian phases, and evenclearances intervals all surprise the unfamiliarmotorist. Local drivers know the condition and stayput until the light changes to green. But visibility ofthe crossing movement signal induces inappropriatebehaviour of those unfamiliar with the signaloperation.

Another example of an unexpected traffic signalindication is the mid-block signal. In most instances,drivers do not expect a traffic signal anywhere butat an intersection. When a mid-block signal is used,they will not be prepared without conspicuousadvance warning, and might not react in time ormight rear end another vehicle stopped in thecrosswalk.

Signs that provide information at the guidance level(regulatory and warning signs) as well as at thenavigational level (guide signs) have the potential tostructure and to violate driver expectancies. Forexample, drivers generally expect to be able toexceed the advisory speed safely when one isposted beneath a curve warning sign. Theseexpectancies are, of course based on one’sexperience. Advisory speed warning plates in NorthAmerica are usually conservative when it comes toa safe speed under most conditions.

There are locations where the warning messagerequires special emphasis. Curves where the advisoryspeed should be adhered to, even in dry weather, andunexpected situations beyond a curve or crest verticalthat would surprise drivers are two examples wheresuch special emphasis is justified, i.e., something thatsays, “this time we really mean it.” Special displaytreatments such as Chevron Alignment Signs, oversizewarning signs and flashing beacons are used to goodeffect at such locations. For the sake of continuedcredibility of these special emphasis devices, however,their use should be reserved for those locations wheregaining drivers’ attention is particularly important.

2.3 Key Considerations

The development of appropriate highway designs andtraffic control devices that meet driver expectancies orthat tell drivers what to expect is the primary way toaid performance and enhance safety and efficiencyon all Ontario’s highways. Attention should be givento assure consistent design from one segment ofhighway to another. When drivers get the informationthey expect from the highway and its informationsystem, driver response tends to be rapid and errorfree. When drivers get what they do not expect or donot get what they do expect, longer response times,inappropriate responses, confusion and errors are thepredictable result. Key considerations aboutexpectancies include the following:

• Expectancies are associated with all levels of thedriving task and all phases of the driving situation;

• Drivers experience problems and commit errorswhen they are surprised;

• Drivers anticipate upcoming situations and eventsthat are common to the route they are driving;

• The more predictable the design, informationdisplays or traffic operation, the less likely will bethe chance for driver error;



• In the absence of information to the contrary,drivers assume they will have to react only tostandard (expected) situations;

• The roadway, the information system and theenvironment upstream will structure expectanciesof downstream conditions.

The objective in helping drivers overcome theeffects of expectancy violation is to structure theappropriate expectation through advance warning.When it is not possible to give drivers what theyexpect, it is imperative to tell them what theyshould expect.

2.4 Failures at the Guidance Level

A guidance level failure occurs when the driverchooses an inappropriate speed or path. The failuretranslates to improper, inadequate or inappropriatecontrol actions. This kind of failure does not implydriver fault. When an accident occurs because ofwrong control action, it might be caused by certaininadequacies in relevant information available to thedriver. Such inadequacies include too muchinformation, too little information, ambiguity,conflicting information, the improper location ofinformation, and information not visible underambient conditions. It is the function of PositiveGuidance to enhance safe driver performance byproviding appropriate, usable information that wouldreduce those failures that are not driver caused.

Two limitations to Positive Guidance are importanthere. First, driver failures due to driver impairmentare not necessarily amenable to correction byproviding improved highway information. Driverswho are drunk, drugged or drowsy or whose normalperformance is otherwise impaired have problemsthat are not usually solved by better signs andmarkings, although there are exceptions to thisgenerality. Second, certain highway design featuresexceed driver response capabilities. Where the

design complexity is such that drivers do not haveenough time to make all the judgements required,no solution short of redesign will eliminate frequentaccidents.

2.5 Information at the Guidance Level

At the guidance level of performance, drivers selectand process information with the objective ofpicking out and maintaining a speed and path theyconsider to be safe, efficient and comfortable.

Roadway Environment

Drivers gather considerable information from theroadway itself. Drivers’ ability to select anappropriate speed and path depends on their abilityto see the road. Drivers should see the road directlyin front, and see enough of that road at somedistance ahead to predict its alignment, grade, widthand several other factors with a high degree ofaccuracy.

Drivers’ view of the road includes a view of theimmediate environment including shoulder and anyobstacles. This also includes sign supports, bridgepiers, abutments, guide rails and median barriers.Information received from the roadway and itsimmediate environment is used continuously duringperformance at the guidance level.

Traffic Control Devices

Three kinds of devices directly affect guidanceperformance – pavement markings and delineators,regulatory and warning signs, and signals. Guidesigns, associated with the navigation level, indirectlyaffect performance at the guidance level, and as such,are an important source, although lower in primacy.



Traffic

Maintenance of a safe speed and path in response toother vehicles in the traffic stream is a major activityat the guidance level. Information received from othervehicles should be processed by drivers at the sametime as other information related to the driving task.Traffic information might be intermittent orcontinuous, but in either case, it should be integratedwith other guidance information to assure adequacyof speed and path decisions.

2.6 Hazards at the Guidance Level

A hazard is any object, condition or situation thattends to produce an accident when drivers fail torespond successfully. Object hazards can, of course,be fixed or moving. Condition hazards refer toconditions of the major system elements: driver,vehicle or roadway environment. Situation hazardsare combinations of conditions and objects, usuallywith a temporal feature, e.g., a wet pavement or atrain approaching a highway – railroad gradecrossing. It is well beyond the scope of positiveguidance to deal with driver or vehicle conditionhazards. Guidance level condition hazards are onlythose of the roadway environments.

Fixed Objects

This type of hazard is the most obvious since itincludes those objects which are often lethal –bridge rails, piers and other bridge elements, non-breakaway sign supports, large trees, etc. In general,any object that is stationary and accessible isincluded. The fact that some objects are themselvesprotective devices, like guide rails and median barriers,does not mean they are hazard free.

Moving Objects

Anything that could move into a driver’s path fallsinto this category. Driver assessment of what ishazardous is relatively simple for the fixed objecthazard, but somewhat more complex for themoving object hazard. Further, the decision processinvolved in avoiding a moving object hazard is alsomore complex in that drivers are required toevaluate the speed and path of the moving object,make corrections in their own speed and path andre-evaluate. This iterative process is well within thecapability of most drivers but can consume muchmental processing time and capacity.

When seen, the object hazard is the simplest hazardto deal with. While the decision making process iscomplex under some situations, the identification ofwhat is hazardous is usually rapid and error free.Unfortunately, perception of highway condition andsituation hazards is neither simple nor without error.

Highway Conditions

The condition of the highway, its design featuresand its state of maintenance or repair, irrespective ofany obstacles, contribute to consideration of theroadway environment as a hazard. Included are:

• Design features such as tangential off ramps orlane drops and other expectancy violations asmentioned above;

• Accessible roadway features that make it difficultto maintain or regain control of an errant vehiclesuch as pot holes, pavement edge drop off andcurves with inadequate superelevation.

All of these features create perceptual problems andexpectancy violations for drivers. Without positiveguidance, they could be expected to induce drivererror. Any location where the condition of thehighway or its immediate environment needs to be



interpreted as a cause for extra caution or a cause tomodify speed or path significantly should beconsidered as a highway condition hazard.

Situations

This hazard category includes combinations ofconditions with or without objects, and mightinclude a temporary condition such as rain. Asituation hazard could include conditions that takenindividually might be of only moderate concern, butthat in combination are treacherous. Combiningsuch elements as rain, a polished surface, a vehiclewith bald tires and a curve with not quite enoughsuperelevation leads to the kind of situation hazardthat is responsible for many skidding and singlevehicle run-off-the-road type accidents.

Highway-railroad grade crossings are good examplesof the difference between highway condition andsituation hazards. Many crossings have severalhazards associated with them. Elevated tracks,crossings at angles other than 90 degrees, andrough crossings are all conditions that warrant extradriver caution. When they all exist at the samecrossing, the problem is much more serious fordrivers. It is the approach of a train, howeverinfrequent, coming from the acute angle that takesthe crossing to another level of hazard.

Strategic Improvements

Looking at the range of hazards, it is possible todefine the obligation of the Province of Ontario tomotorists on its highways. First, if possible,practicable, and within the financial andprogrammatic ability of the Ministry, the hazardshould be eliminated. If that cannot be done, andthere are many valid reasons for that to be the case,then the hazard should be made inaccessible orforgiving (move it, screen it or make it breakaway). Ifthat cannot be done, and again there are many valid

reasons for that to be the case, particularly withdesign features, motorists should be given enoughinformation to avoid the hazard. It is that informationthat provides positive guidance. Short of closing theroadway to traffic, there are no other alternatives.

2.7 Drivers Avoiding Hazards

Successful performance by drivers is dependentupon their ability to detect a hazard, recognize it orthe threat it poses, decide on an appropriate speedand path, and act on that decision. The principles ofPositive Guidance would require that drivers begiven all the information needed to maximize theselection of appropriate speeds and paths.

Detecting the Hazard

Hazards range in detectability from very easy(seeing a fixed object in the road) to very difficult(seeing a three inch pavement edge drop off atnight). How seeable a hazard is depends on manyfactors including the interaction between its visibility,its conspicuity or target value, and the number ofcompeting information sources. Also included arethe driver’s scanning behaviour, visual acuity, priorknowledge and expectancy. This interaction defineshow detectability of a hazard could be enhanced. Inthe case of a fixed object, making it more visiblemakes it more detectable. With objects andhighway conditions, reducing the number ofinformation sources competing for drivers’ attentiongives drivers more time to detect the hazard. In thecase of any hazard, increasing driver expectancy ofseeing the hazard will improve its detectability. Heresigning and marking play an important role in thehazard detection task.



Recognizing the Hazard

Hazard recognition is a simple name for a complexmental process. Once something has been seen, thedriver should decide what it is. Because recognitionfollows detection in time, the driver is closer to thehazard and could see it better (or more of it), andget more information from it. That information iscompared with the driver’s store of prior knowledge.Prior driving experience becomes increasinglyimportant in recognizing highway condition andsituation type hazards, although some of theknowledge can be gained through driver training.Some knowledge is too situation specific to betaught in driver education, and in those caseshazards are recognized through personal experienceor flagged with a device (usually a warning sign) ornot recognized.

The use of warning signs, and to some extentregulatory signs, carries an implicit warning to thetraffic practitioner who employs them. These signsprepare motorists to detect and recognize hazards.When the hazard is present, the value of thewarning is reinforced. However, when the hazard isnot there or not apparent to drivers, the credibility ofthe warning or regulation is reduced. A typicalexample is work zone signing including reducedspeed warning with no work or workers in sight.

Deciding What to Do

After the hazard is recognized, drivers need todetermine if modification of speed and path isnecessary, and if so, define alternative courses ofaction. If more than one course of action isconsidered, drivers evaluate the probability ofsuccess as well as the ease and comfort ofimplementation. Here, too, experience plays a big role.We all tend to repeat past behaviour that has beensuccessful. Finally, drivers select the speed and paththey consider to be the most appropriate for thesituation. These decisions are frequently made under

great time pressure. Here, it can be seen that thosewho are inexperienced and those whose informationprocessing abilities have deteriorated throughadvanced age or impairment are at a disadvantage.

Doing It

Helping motorists to select the appropriate speed andpath is as far as the Positive Guidance process can go.Vehicle control to implement the decisions is entirelyin the hands of the driver. After taking an action, thedriver evaluates its adequacy, applies a speed or pathcorrection if required, and continues the process untilthe hazard no longer poses a threat or a higherprimacy need interferes. There is a great deal ofinformation handling in this process, some at theguidance level, much at the control level.

2.8 Planning, Design and Construction

Although the Positive Guidance procedures containedin Sections 3 onward are designed to be used bytraffic operations personnel, the concept andprinciples, as defined above, are equally important inthe planning, design and construction phases ofproject development. Traffic control devices areusually considered the principal means ofcommunicating with motorists. However, thehighway itself conveys more information to itsusers than any other single source!

Planners and designers whose job it is to determinewhat the highway will look like, therefore, play a keyrole in the development of highway relatedinformation. In fact, any activity, whose outputconveys information related to the driving task tohighway users, is an activity that has potential forproviding positive guidance, whether or notinformation giving is its primary intent. For example,although the principal purpose of the placement ofguide rail is the physical protection of motorists from



fixed object hazards and the redirection of errantvehicles, there is no question that its placement andappearance give motorists important guidanceinformation. The information imparted is positiveguidance when it assists highway users in makingcorrect speed and path decisions to avoid hazards.Here, it is no more or less an example of positiveguidance than a line of reflectorized barrelsdelineating the temporary edge of travel lane in awork zone.

The alignment and profile relationships of anyhighway are crucial to the formulation of accuratedriver expectancy. Together, and in combinationwith other features such as superelevation, signs,markings and roadside grading, they provide thepositive guidance drivers need to conduct the tasksafely and efficiently. It is essential, therefore, that allthe elements act in concert. For example, an urbanor suburban facility should not be planned ordesigned to give the impression of a higher typefacility than the posted speed limit would warrant.The ambiguity created by an apparent high typefacility and relatively low speed limit violates driverexpectancy, creates credibility problems and invitesspeeds higher than can safely be accommodated.

3. Procedures

There are two phases to the procedures described inthis section of Appendix C, project planning and datacollection, and data analysis. Project planning anddata collection ranges in magnitude from small,informal studies to large, labour intensive studieswith precise data gathering requirements. At itssimplest level, collecting historical data is just amatter of gathering office records pertaining to thesite to be studied. Other data are collected on sitethrough detailed inspection and a review ofoperations. Both historical data and site inspectionand review data are discussed in this section.However, if the project is to undergo a full scaleeffectiveness evaluation, a formal data collectionplan and procedure becomes a part of the project.Although it is considered essential to conduct anappropriate effectiveness evaluation of the project ifits results are to be applied elsewhere, formal datacollection procedures and statistical treatments arenot discussed here. See ITE’s Manual on TrafficEngineering Studies for detailed discussions on theconduct of effectiveness evaluations.

The second phase analyzes the data. The analyticprocedure consists of the following eight steps:

(1) Identifying the Hazards;

(2) Determining Land Use and HazardousAvoidance Manoeuvres;

(3) Specifying Information Handling Zones;

(4) Rating Hazard Visibility;

(5) Determining Expectancy Violations;



(6) Analyzing Information Loads;

(7) Identifying Information Needs;

(8) Evaluating the Current Information System.

It should be noted that the analytic procedure itselfdoes not extend to the ninth step, the developmentof improvements or a traffic control plan for the siteunder study. The value of this procedure is seen inthe detailed site and needs analyses, which whencombined with the principles contained in Section 2allow the full range of engineering judgement to beapplied to the problem.

A Positive Guidance project is usually initiated whena location with information system problems hasbeen identified and selected for further review:

• Road Safety Audit, routine surveillance, designreviews, corridor or formal operations reviewsidentify locations with information systemdeficiencies.

• Accident analyses identify high accident locationsand locations with high accident potential, e.g.,narrow bridges and railroad grade crossings.Further investigation indicates that there might bedeficiencies in the information system orrestrictions in sight distance.

• Delay, congestion, or indications of driverdirectional confusion such as erratic manoeuvreand lost motorists identify locations where drivernavigational uncertainty might contribute tothroughput or traffic operations problems.

• Citizen complaints or feedback from police ormaintenance personnel identify locations withinformation system deficiencies or driverconfusion.

3.1 Project Planningand Data Collection

This phase of the project houses the data collectionplan, an office review, and a site survey andoperations review.

Data collection requirements vary from project toproject. All projects require available historic data aswell as data from the site survey and operationsreview. Additional performance data might beneeded for diagnostic purposes, depending on datagaps identified by the historical review. Effectivenessdata are required when statistical evaluations areperformed. Although this type of evaluation isoptional, it should be performed whenever possible.It determines whether, and to what extent, the site’sproblems have been reduced or eliminated and alsoprovides input to the road authority’s database.

There are three data collection strategies andassessments used to implement the PositiveGuidance procedure:

(1) Historic data collection and review;

(2) Informal field data collection and review;

(3) Performance data collection and analysis.

Data Collection and Office Review

The historic data review uses existing accident,complaint, and engineering data to specify whatsafety and operational problems have occurred,where they have occurred, and when (time of day,day of week, time of year) they have occurred. Thereview could also serve to identify target groups ofdrivers (e.g., older drivers, truck drivers) or vehicles(e.g., trucks, motorcycles) experiencing difficulties.Finally, the historic data review can help identifyconditions under which problems are occurring(e.g., weather, lighting).



The office review task should assemble existing siteinformation, generate an initial condition diagram,develop a collision diagram/accident summary, andproduce a list of “things to look for and at” for use inthe site survey and operations review. Informationdeveloped during this activity is used to define thesite in terms of land use, road type, and geometry.This information is also used to develop or verify thecondition diagram, and to provide a framework forsubsequent activities. In defining the project site, thefollowing elements are identified:

• Land use (rural, urban or suburban);

• Road type and number of lanes (e.g., four lanedivided arterial);

• Geometric Characteristics, including alignment,grade, at-grade crossings, changes in crosssection, interchanges, intersections, off-roadfeatures, structures, turns, and other specialcharacteristics.

These elements form the basis of the initialcondition diagram which includes all the relevantsources of information and their location.

Assembly of Existing Site Information

Applicable existing site information and data shouldbe assembled and reviewed. This activity appliesonly to existing data and does not require any datacollection effort. This informal review providesinsights about the site’s characteristics, operations,and problems, and can also identify requisite data tobe collected in subsequent phases.

Initial Condition Diagram

Information from suitable plans or aerial photos anda traffic control device inventory, if available, shouldbe used to develop an initial condition diagram. As

the procedure is applied, this diagram will be used tolocate traffic control devices and other pertinentfeatures such as hazards, furniture, and terrain.

Collision Diagram/Accident Summary

Suitable accident summaries and/or collisiondiagrams should be obtained or generated, if at allfeasible, during the office review. A review of thisinformation helps to identify and describe problemsand aids in data collection in later activities.

List of Things to Look For and At

A site specific list of things that should be looked foror inspected during the conduct of the site surveyand operations review should be developed. The listmight include: specific accident locations, placeswhere accidents cluster, traffic control devicelocations, hazards and hazard locations, sightdistance/sight distance restrictions, sign blockage,horizontal and vertical alignment, driver confusionsources (geometry and information), speeds, erraticmanoeuvre, encroachments, conflicts, pavement/shoulder width and condition, environmentalconditions, and potential data collection locations.

Project File

A project file should be started at the beginning ofthe Positive Guidance project to document andsummarize all aspects of the effort. Throughout theproject, each activity should be documented in atimely manner to assure that the file is accurate andup to date. This will aid in developing improvementsand writing a project report, when applicable.

Site Survey and Operations Review

These are the first data collection activities at thesite. Using an appropriate informal field datacollection technique as listed below, a drive throughis conducted in order to:



• Experience the problems an unfamiliar motoristmight encounter;

• Perform an expectancy violation review;

• Observe the manner in which drivers manoeuvrethrough the site. Take notes and pictures.

Informal Field Data Collection

A drive-through and an operations review are usuallyperformed, and additional informal field reviews areoften conducted in the course of the problemdescription activity.

• Drive-throughBeginning upstream and ending downstream of aproblem location, all paths and directions of thesite are driven, and a “driver’s-eye” view of hazardsand highway information sources is obtained.Notes of what is seen are prepared, photographsof important features are taken, and the conditiondiagram is completed during this review.

• Commentary Drive-throughThe commentary drive-through is a similar, morestructured field review, where an audio or videowith sound is made to provide a running verbalcommentary of what is seen at the site. Suchthings as extremes in the site’s geometry, unusualmanoeuvres, hazards, and deficiencies in theinformation system are “flagged” for furtheranalysis. When an audio recording is used, itshould be supplemented with site photos.

• Walk-throughA walk-through is a supplementary effort, wherethe site is surveyed on foot to note accidentdebris, guide rail dents, skid marks, and otherfeatures or problem indicators that might not beapparent from a vehicle.

• Site SurveyDuring a site survey, information from thehistorical data review is used to identify whatproblems the site is experiencing and specificallywhere they are occurring. The site is visited, itsphysical characteristics surveyed, and operationsat the problem location observed from anunobtrusive vantage. The purpose of this activityis to watch traffic in order to gain insights aboutspeeds, paths, and directions.

• Operations ReviewThe operations review is more structured than thesite survey in several respects. The site isobserved at the times that most problems seemto be occurring, e.g., peak periods or at night.Additionally, a small sample of performance data(e.g., speed, erratic manoeuvre, traffic conflicts) iscollected to obtain an indication of problems suchas excessive speed and directional uncertainty(e.g., more than 3% of the sample commit erraticmanoeuvre at an interchange). Locations forperformance data collection are also identified.

Performance Data Collection

Performance data are usually collected to fill in datagaps, to aid in problem diagnosis, and/or when aneffectiveness evaluation is applicable. A datacollection plan should always be developed,including traffic volume collection used todetermine exposure. When an evaluation isapplicable, performance data to be collected formeasures of effectiveness should be identified anddefined. Volume III of the MOE’s U.S. FHWA’s Serieson Positive Guidance, Planning and Field DataCollection and ITE’s Manual of Traffic EngineeringStudies provide details on all aspects ofperformance data collection.



• Data Collection PlanThe plan should account for:

• representative conditions to replicate the times;

• locations, and circumstances of problemoccurrence;

• unobtrusive vantages to assure that the trafficstream is unaware of the data collection;

• appropriate data collection methods that aresuitable for the needs of the project;

• sufficient data for diagnosis and evaluation;

• details of field crews, equipment, procedures,and schedules.

• Applicable Data to CollectTable 1 tabulates traffic performance measuresthat are usually collected as Measures ofEffectiveness (MOE) for a range of sitecharacteristics. Performance data needs are alsodetermined by an assessment of what informationis needed for diagnostic purposes. Generally,speed and volume data are considered baseline,and are not included in the table. In addition,applicable data to collect are also determined bythe needs of a particular study. For example, thedocument Traffic Conflicts Techniques for Safetyand Operations specifies the kinds of datarequired for a traffic conflicts study.



Table 1 – Traffic Performance Measures

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Table 1 – Traffic Performance Measures (cont’d)


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Table 1 – Traffic Performance Measures (cont’d)


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3.2 Applying the PositiveGuidance Procedure

The Positive Guidance procedure provides a step-by-step assessment of a driver’s task negotiating aproblem location, thereby identifying driver-relatedproblems caused by deficiencies in the site’sinformation system.

Most of the activities are augmented by a checklistthat can be filled out in the field or completed in theoffice after reviewing, documenting, andphotographing field conditions and operations.Checklists are discretionary tools, and arerecommended for use at visually complex and highaccident locations. The information generated bythe checklists is used to focus and help formulateactivity outputs and products. There may be projectswhere, at the discretion of the user, some activitiescould be combined or eliminated.

Identifying the Hazards

Information for identifying hazards is obtained fromhistorical data, and from notes, comments, slides,photographs, and videos taken during the drive-through. Hazard-related information is usually

gathered after the initial drive-through has beenconducted and problem definition findingsdeveloped, since the products of these activitiesprovide insights on the site’s hazards and hazardclusters. Checklist 1 serves as a framework forhazard identification and threat assessment.

Identification of Hazards and Inefficiencies

Hazards and hazard clusters are identified and theirthreat or threat potential determined by historicaldata analysis, field observation, and engineeringjudgement. For example, individual accident reportshelp identify fixed and moving objects involved incollisions and provide information regardingconditions contributing to problems. Accident plotspoint to specific problem locations and are useful foridentifying hazard clusters. Drive-through andoperations reviews verify accident and complaintfiles and also enable an identification to be made ofobvious hazards such as trees and traffic, and lessobvious ones such as short signal phases, culverts,and potholes. Photographs and slides provide viewsof hazards that may be missed during field review.

• Fixed ObjectsFixed objects are generally the most readilyidentifiable type of hazard. Their threat is

Table 2 – Fixed Object Hazards

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determined by their size, location, accessibility,proximity, forgiveness, and collision-consequence.Table 2 lists common fixed object hazards.

• Moving ObjectsMost moving object hazards, shown in Table 3,are associated with traffic. Vehicles potentially inconflict, such as cross-traffic, turning traffic,merging traffic, encroaching vehicles, etc. posethe greatest threats. In many locations, othermoving hazards such as pedestrians, bicyclists,trains, and animals are significant. A finer-grainedidentification of moving object hazards, e.g., out-of-province trucks, young children, olderpedestrians, tour buses, is also useful. Threat isassessed on the moving hazard’s actions as wellas its size and speed, e.g., a truck’s last minutelane change, a pedestrian crossing mid-block, etc.Because moving hazards are transitory, and mayrarely occur in low-volume situations, they can bedifficult to capture during a drive-through. In thesecases, their identification and threat assessmentwould be based on historic data and engineeringjudgement. At intersections, a traffic conflictsstudy is often used to identify accident potential.

• Highway ConditionsHighway and traffic condition hazards are oftendifficult to identify because: they may not be

readily apparent, e.g., a queue of traffic stoppedbeyond a crest vertical curve; they may betransitory in nature, e.g., potholes, maintenanceoperations; or they may not be associated withaccidents, even though their accident potential ishigh, e.g., a narrow bridge, a railroad gradecrossing. However, an experienced reviewer cangenerally spot condition hazards in the course of adrive-through. It is noted that many of the sourcesof expectancy violation, considered in subsequentactivities, are actually condition hazards. Table 4shows common condition hazards.

• Situation HazardsSituation hazards are usually the most difficult toidentify and assess because they consist of fixedand/or movable objects in combination withcondition hazards and may only occur underadverse environmental conditions. In many cases,the individual hazards are not a problem withoutfog, rain, snow, ice, blowing sand, smoke,darkness, etc. For example, overpasses aregenerally not hazardous until they freeze. Sincesituation hazards are transitory and often seasonal,it might not be possible to observe the site whenit is hazardous. This requires a reliance onhistorical data, experience, and engineeringjudgement for situation hazard identification.

Table 3 – Moving Object Hazards

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• Inefficient OperationsAlthough hazard identification emphasizes safety-related hazards, it also addresses navigationproblem sources that can result in inefficienttraffic operations. It does not, however, addressthroughput problem sources (incidents, excessdemand, insufficient capacity).

Inefficiencies are caused by and result in lost orconfused drivers, less than optimum routing, wastedfuel, path confusion, and excess delay and traveltime. Navigation problems are generally associated

with choice points, i.e., intersections and interchanges.Problems can be caused by deficiencies in advancedguide signs, inadequate forward sight distance, poorchoice point information, or path confusion at thechoice point. Inefficient operations caused bynavigation deficiencies are identified from complaintfiles, drive-through, and observing erratic manoeuvre,brake applications, slow driving, and tire marks on thepavement approaching or at the choice point.

Table 4 – Highway and Traffic Condition Hazards

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Determination of Significant Hazard Clusters

Often, several hazards occur in such close proximitythat they affect drivers as if they were one hazard. Inthis case, they are considered to be a hazard cluster.Constructing a hazard profile is an optional effortundertaken to identify or verify the existence ofsuspected clusters. The profile is generated bypositioning all hazards in a given location along theX axis of a graph calibrated in distance units. Whenhazards overlap, they are plotted as hazard levels,along the positive Y axis. Accidents associated with

a hazard are plotted on the negative Y axis, calibratedin accident frequency. The resultant profile of hazardsplotted against accidents provides a graphic displayof clusters (See Figure 7). However, it must beemphasized that there are often problems inherent inlocating accidents from accident reports. Therefore,the profile should serve primarily as an indicator of acluster’s existence, and secondarily as an indicator ofits location.

Figure 7 – Hazard Profile

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Checklist 1 – Hazard Identification

Fixed Object (Accessible and Unprotected):

❏ Tree ❏ Utility Pole ❏ Parked Vehicle

❏ Sign Post ❏ Guide Rail End ❏ Bridge Abutment

❏ Curb ❏ Barrier ❏ Wall

❏ Other ______________________________________________________________________

Moving Object (Accessible and Unprotected):

❏ Cross Traffic ❏ Turning Traffic ❏ Merging Traffic

❏ Slow Moving/Stopped Traffic ❏ Trucks, Buses, etc. ❏ Railroad Trains

❏ Pedestrians ❏ Bicycles ❏ Animals

❏ Other ______________________________________________________________________

Highway Condition (Conditions Requiring Significant Speed/Path Modification):

❏ Inadequate superelevation ❏ Sharp Horizontal Curve ❏ Steep Grade

❏ Deficient Sight Distance ❏ Lane Width Reduction ❏ Mainline Lane Drop

❏ Inadequate Shoulder ❏ Inadequate Recovery Area ❏ Pothole

❏ Poor Drainage ❏ Worn Pavement ❏ Accessible Ditch

❏ Inadequate Diverge ❏ Optional Lane ❏ Short Weave

❏ Sharp Off-ramp Angle ❏ Tight Radius Loop Ramp ❏ Left-on Ramp

❏ Contraflow Lane ❏ Uncontrolled Intersection ❏ Narrow Bridge

❏ One-lane Bridge ❏ Draw Bridge ❏ Low Clearance

❏ Weight Restriction ❏ Work Zone ❏ School Crossing

❏ Railroad Crossing ❏ Pedestrian Crossing ❏ No-passing Zone

❏ Falling Rock Zone

❏ Other ______________________________________________________________________



Checklist 1 – Hazard Identification (cont’d)

Situation (Combination of Objects, Conditions,and/or Environmental Effects):

❏ Icy Pavement ❏ Snow Covered Pavement ❏ Slippery Pavement

❏ Fog Area ❏ AM/PM Sun in Drivers’ Eyes ❏ Standing Water

❏ Headlight Glare ❏ Object or Condition Beyond Crest Vertical

❏ Train in Unprotected Crossing

❏ Other ______________________________________________________________________

Inefficiency (Feature that Leads to Directional Problems):

❏ Tangential Off Ramp ❏ Left Exit ❏ Exit Lane Drop

❏ Optional Lane Split ❏ Congested Intersection ❏ Detour

❏ T- or Y-Intersection ❏ Offset Intersection ❏ Circle or Roundabout

❏ Other ______________________________________________________________________

Significant Hazards

List significant hazards and hazard clusters from preceding categories.

Fixed Objects: _________________________________________________________________________________________________________________________________________________

Moving Objects: _______________________________________________________________________________________________________________________________________________

Highway Conditions: ____________________________________________________________________________________________________________________________________________

Situations: ____________________________________________________________________________________________________________________________________________________

Inefficiencies: _________________________________________________________________________________________________________________________________________________



Assessing Hazard Visibility

This part of the procedure is used in conjunctionwith Checklist 2 to determine whether hazard andhazard cluster visibility is adequate for a problemlocation’s driving task requirements. When visibilityis found to be inadequate, the assessment alsoprovides criteria for the placement of advancewarning information.

The objective of this activity is to assess each hazardand hazard cluster to determine if it can bedetected, recognized, and its threat potentialassessed in sufficient time for drivers to respondsafely and efficiently. This assessment is made usingland use, hazard avoidance manoeuvre, and speedto determine decision and stopping sight distance.

Determining Land Use andHazard Avoidance Manoeuvre

A determination is made of the site’s land use,which serves as a surrogate for visual clutter. Landuse is categorized as rural (low clutter), suburban(moderate clutter), or urban (high clutter). Followingthis determination, a judgement is made as towhether the appropriate hazard avoidancemanoeuvre is a stop or a change in speed, path ordirection. For example, approaching an occupiedrailroad grade crossing, the appropriate manoeuvrewould be to stop. On the other hand, theappropriate manoeuvre at a freeway exit or lanedrop could be a path and directional change.

Specify Applicable Sight Distance Case

The land use/hazard avoidance manoeuvredetermination is used to specify the applicable sightdistance case from Table 5.

Determine Approach Speed

In order to specify stopping and decision sightdistances, the 85th percentile approach speed tothe hazard or hazard cluster is determined androunded to the higher 5 km/h increment.

The 85th percentile speed can be determined froma cumulative frequency distribution of spot speedsfrom a representative sample collected for theproject, or from existing data, if available.

The 85th percentile speed can be calculated fromexisting mean speed (M) and standard deviation(SD) data using the formula:

85th Percentile Speed = M + [1.1 x SD]

If no data exist or can be collected, the 85thpercentile speed may be estimated from the trafficstream, using the posted speed as a guide.

Determine Stopping and Decision Sight Distance

Once the case and 85th percentile speed has beenderived for significant hazards and hazard clusters,stopping and decision sight distances are obtainedfrom Table 6. This table presents desirable decisionsight distance and calculated stopping sightdistance values for cases A through E and for a

Table 5 – Sight Distance Case

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B nabrU/nabrubuS potS

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E nabrU noitceriD/htaP/deepS



range of approach speeds from 50 km/h to 110 km/h. (As discussed in the AASHTO Green Book andadapted for use in Ontario.)2

Specifying Information Handling Zones

Five information handling zones are used to assess ahazard/hazard cluster’s visibility and to locatehazard-associated information. Hazard visibility isultimately rated on what zone the driver is in whenhe/she can first detect it, recognize it as a hazard,and recognize its threat; and where in the zone thisoccurs.

• Advance Zone – The advance zone is upstream ofthe hazard, beyond the decision sight distance. Atbest, a hazard might be visible toward thedownstream end of the zone. This zone is used todisplay low primacy and supplemental informationand to structure expectancies.

• Approach Zone – The approach zone is upstream ofthe hazard, beginning at the start of its decisionsight distance and ending at the start of itsstopping sight distance. Optimum hazard visibilityshould occur at the end of the advance zone or atthe beginning of the approach zone. When thehazard is not visible, advance hazard warninginformation should be located in this zone.

• Non-recovery Zone – The non-recovery zone isupstream of the hazard, beginning at the start ofits stopping sight distance and ending at thehazard. The hazard’s visibility is sub-optimum inthis zone, particularly approaching the hazard.Speed and path information is displayed in thiszone.

Table 6 – Stopping and Decision Sight Distance Values

2 A Policy on Geometric Design of Highways and Streets; Washington, DC: American Association of State Highway andTransportation Officials, 1990, pp. 125 to 127.

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A B C D E

05 56 76 251 731 251 091

06 58 501 122 381 122 152

07 011 821 952 502 342 282

08 531 251 792 822 572 213

09 061 871 853 772 023 853

001 581 702 693 503 053 983

011 512 572 564 533 693 244



• Hazard Zone – The hazard zone encompasses thehazard. Information in this zone enhances hazardvisibility through lighting, clearing sight lines,painting, hazard markers, etc.

• Downstream Zone – The location beyond thehazard is its downstream zone. This zone isprimarily used for route confirmation, “pull-through”, and low primacy information.

Rating Hazard Visibility

Using the stopping and decision sight distancevalues, a hazard-specific information handling zonediagram is developed. A drive-through is conductedto determine where the hazard is first visible andrecognizable. The distance from this point to thehazard is measured, noted on the checklist,positioned on the diagram, and used to assess thehazard’s visibility. Generally, the further upstream thehazard is detectable and recognizable, the better isits visibility.

Visibility Rating Scale – A five-point scale is used torate how well a hazard can be detected andrecognized:

1 = Excellent Visibility (detectable andrecognizable in the advance zone);

2 = Good Visibility (detectable and recognizableearly in the approach zone);

3 = Fair Visibility (detectable and recognizable latein the approach zone);

4 = Poor Visibility (detectable and recognizableearly in the non-recovery zone); and

5 = Very Poor Visibility (detectable andrecognizable late in the non-recovery zone). If thehazard’s visibility rating is poor, the assessment isused to position advance hazard warninginformation. The encircled numbers in Figure 8shows the visibility rating scale relative to theinformation handling zones.

Figure 8 – Information Handling Zones

Advance Zone Approach Zone Non-recovery Zone Hazard Zone Downstream Zone

2 431 5



Checklist 2 – Hazard Visibility Assessment

Hazard Avoidance Manoeuvre

Assess each hazard or hazard cluster separately. Note significant hazards from Checklist 1.Start with hazard closest to reviewer and work downstream.

Determine Case from Tables 3 to 5.

Hazard(s) or Hazard Cluster(s) Case

a. _________________________ A ❏ B ❏ C ❏ D ❏ E ❏

b. _________________________ A ❏ B ❏ C ❏ D ❏ E ❏

c. _________________________ A ❏ B ❏ C ❏ D ❏ E ❏

d. _________________________ A ❏ B ❏ C ❏ D ❏ E ❏

e. _________________________ A ❏ B ❏ C ❏ D ❏ E ❏

Specify posted, estimated or 85th percentile speed (km/h)

50 ❏ 60 ❏ 70 ❏ 80 ❏ 90 ❏ 100 ❏ 110 ❏

Determine Stopping and Decision Sight Distance for applicable speed and case from Tables 3 to 6.

Sight DistanceHazard(s) or Hazard Cluster(s) Stopping Decision Visible

a. _________________________ _________ _________ _________

b. _________________________ _________ _________ _________

c. _________________________ _________ _________ _________

d. _________________________ _________ _________ _________

e. _________________________ _________ _________ _________



Determining Expectancy Violations

The expectancy violation determination is designedto find out whether general, widely-held populationexpectancies are violated, and whether site-specificexpectancies structured upstream of a problemlocation are violated downstream in the vicinity ofthe site being assessed. Data for this activity arecollected from drive-through of the problem locationand adjacent areas in all directions, often beginningat points considerably upstream of the site. Inperforming this step, each hazard should beassessed, and less obvious expectancy violationsources should be searched for. A key determinationto make is whether drivers are being surprised byaspects of the site. Checklist 3 is used to help makethese determinations.

The objectives of this activity are to obtain, throughthe performance of a general expectancy review, anoverall impression of the area adjacent to theproblem location, and to note potential sources ofexpectancies and expectancy violations; and to

focus in on the area immediately upstream of theproblem site to identify, through the performance ofa detailed expectancy violation determination,sources of site-specific expectancies, and todetermine whether these, and/or populationexpectancies have been violated downstream atthe site.

General Expectancy Review

The general expectancy review is initiated wellupstream of the problem location. Its purpose is toobtain a “feel” for areas that drivers will be passingthrough before negotiating the site. The generalreview should be accomplished from theperspective of a “stranger” who is unfamiliar withthe area and road network. As much of the roadthat the problem is located on, upstream anddownstream, and as much of the surrounding areaas possible should be reviewed. If the problem site isin a low density rural location, the review shouldstart several miles upstream, possibly where theroad with the problem site junctions with a major

Checklist 2 – Hazard Visibility Assessment (cont’d)

Rate each hazard or hazard cluster in terms of its upstream visibility. 1 is the best, 5 is the worst.

Hazard(s) or Hazard Cluster(s) Rating

a. _________________________ 1 ❏ 2 ❏ 3 ❏ 4 ❏ 5 ❏

b. _________________________ 1 ❏ 2 ❏ 3 ❏ 4 ❏ 5 ❏

c. _________________________ 1 ❏ 2 ❏ 3 ❏ 4 ❏ 5 ❏

d. _________________________ 1 ❏ 2 ❏ 3 ❏ 4 ❏ 5 ❏

e. _________________________ 1 ❏ 2 ❏ 3 ❏ 4 ❏ 5 ❏



primary route. If the problem site is in a high densityurban location, the review should encompass asmuch of the adjacent street, arterial, and freewaynetwork as possible, as well as several miles of thefacility upstream of the problem. If the problemlocation is close to a jurisdictional boundary such asa provincial or district line, the general review shouldbegin in the adjacent jurisdiction to note if changesoccur across the boundary.

The general review is informal and can beperformed in conjunction with drive-through fromprevious activities. However, it should be conductedwhen problems are occurring, such as during peaks,or at night. It is best to use pencil and paper orcommentary driving to record observations, to takepictures of significant features, and to locate them

relative to the problem site. The key in the generalreview is to identify changes and/or different orunusual practices that could affect expectancies.

Table 7 lists factors that should be considered interms of changes from upstream to the site. Thistable could be brought to the field as an informalchecklist. When general expectancy violations arefound, they should be flagged for furtherassessment during the detailed expectancy violationreview.

Table 7 – General Expectancy Review Factors

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Checklist 3 – Expectancy Violation Determination

1. Are there unusual features or attributes that drivers find surprising?

❏ Intersections ____________________________________________________________

❏ Interchanges ___________________________________________________________

❏ Geometric Extremes _____________________________________________________

❏ Manoeuvre _____________________________________________________________

❏ Cross Section Changes ___________________________________________________

❏ Roadway Environment Changes ____________________________________________

❏ Regulatory Changes _____________________________________________________

❏ Off-line Restrictions ______________________________________________________

❏ Climatological __________________________________________________________

❏ Traffic Patterns/Vehicle Mixes _____________________________________________

❏ Lighting _______________________________________________________________

❏ Terrain Features _________________________________________________________

❏ Miscellaneous Features ___________________________________________________

2. Are there first-of-a-kind features?

3. Are there changes in the road that could surprise unfamiliar drivers?

❏ Land Use ______________________________________________________________

❏ Road Type _____________________________________________________________

❏ Road Surface ___________________________________________________________

❏ Cross Section ___________________________________________________________

❏ Operating Practices ______________________________________________________

4. Are there unexpected geometric inconsistencies?

5. Do any existing traffic control devices violate driver expectancy?

❏ Regulatory and Warning Signs _____________________________________________

❏ Guide Signs ____________________________________________________________

❏ Traffic Signals __________________________________________________________

❏ Markings/Delineation ____________________________________________________



❏ Work Zone Devices ______________________________________________________

❏ Other _________________________________________________________________

6. Is any aspect of the route-following and direction-finding task surprising? Specify.

__________________________________________________________________________

Expectancy Violation Visibilty

7. Rate each expectancy violation feature in terms of its upstream visibility. 1 is best, 5 is worst.

Expectancy Violation Feature Rating

a. _________________________ 1 ❏ 2 ❏ 3 ❏ 4 ❏ 5 ❏

b. _________________________ 1 ❏ 2 ❏ 3 ❏ 4 ❏ 5 ❏

c. _________________________ 1 ❏ 2 ❏ 3 ❏ 4 ❏ 5 ❏

d. _________________________ 1 ❏ 2 ❏ 3 ❏ 4 ❏ 5 ❏

e. _________________________ 1 ❏ 2 ❏ 3 ❏ 4 ❏ 5 ❏

Advance Warning

8. Is there advance warning of unexpected features? ❏ Yes ❏ No

9. If Yes, is it adequate? ❏ Yes ❏ No

10. Specify deficiencies: __________________________________________________________

Overall Rating

11. Overall rating of site’s expectancy violations.

❏ No Expectancy Violation Problem

❏ Minor Expectancy Violation Problem

❏ Major Expectancy Violation Problem

Checklist 3 – Expectancy Violation Determination (cont’d)



Detailed Expectancy Violation Determination

The difference between the general review and thedetailed expectancy violation determination is thatthe detailed determination is more focussed,considers a much smaller area, and builds on theresults of the general review. The detailed reviewusually starts at a convenient spot in the advancezone. It can be conducted in the field during a drive-through or in the office using suitable site photos,slides, or videos. In performing the review, the site-specific questions shown below, pertaining toexpectancy violations and their sources, surprises,and first-of-a-kind features, such as those shown inTable 8, should be addressed. The adequacy of anyadvance warning and the visibility of expectancyviolation sources are also rated.

• Does the site contain features or attributes thatdrivers might find unusual or special? Describe.

• Are there first-of-a-kind features? What are they?

• Are any features or attributes surprising? Describethem.

• Are there changes in the site’s characteristics?What are the changes?

• Are there changes in the site’s operatingpractices? What are they?

• Are there forward visibility restrictions? Describethem.

• Is there advance warning? Is it adequate?

The output of this activity is used to identify whatexpectancy violations require restructuring, andwhat the sources of the violations are. It addresseswhether sources upstream of the problem locationmight have to be changed.

Information Load Analysis

Data for this activity are developed from a drive-through, using Checklist 4 to assess load factorsand rate load potential. The factors serve assurrogates for processing load, thereby eliminatingthe need to count information sources and gaugetheir information content. Factors are assessedqualitatively, based on whether a low, moderate, orhigh information load is imposed. The individualload factors and overall site ratings are derived usingengineering judgement.

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Table 8 – First-of-a-Kind Features



The objectives of this activity are to analyse the sitein terms of a number of information load factors andrate its overall load potential. The overall site loadpotential is based on the number of load factorratings in each processing load category. If virtuallyall factors are low, the site would have a potential for“underload,” if virtually all factors are high, the sitewould have a potential for “overload,” and, if mostfactors are moderate, there should not be any loadproblems at the site. The information load analysis iscomprised of the following:

Information Load Factors

• Land Use

• Access Control

• Volume

• Speed

• Task/Manoeuvre

• Number of Hazards

• Hazard Visibility

• Sight Distance

• Expectancy Violations

• Clutter

• Competition

• Complexity

Individual Factor Ratings

• Low

• Moderate

• High

Overall Site Ratings

• Probable Underload (all factors rated low)

• Possible Underload (most factors rated low)

• No Load Problems (most factors rated moderate)

• Possible Overload (most factors rated high)

• Probable Overload (all factors rated high)

Information Load

Driver performance is usually most consistent,reliable and predictable when there is a steady,moderate level of information to process. Sinceprocessing capability varies from driver to driver, it isnot possible to specify with precision how manyinformation sources or how much informationcontent per source is too little or too much. It is alsodifficult to tell which or how many sources ofinformation a driver is attending to, and theinformation content of an individual source. One ortwo sources is usually considered a low informationload, and more than seven to nine sources is usuallyconsidered a high information load.

Rather than counting all information sources andquantifying each source’s information content, inbits, the information load analysis uses a qualitativeapproach. It estimates the processing load imposedon the driver from a number of site-related factorsand uses the aggregate of these estimates todetermine the site’s overall processing load. Theindividual factor and overall ratings are derived usingengineering judgement, with the overall ratingbased on how most of the factors are rated:

• Low Load – If most or all factors are rated low,there is an underload possibility.

• Moderate Load – If most or all factors are ratedmoderate, there should be no load problems.

• High Load – If most or all factors are rated high,there is an overload possibility.



Checklist 4 – Information Load Analysis

1. Evaluate information processing load factors:

Low Moderate High

a. Land Use ❏ Rural ❏ Suburban ❏ Urban

b. Access Control ❏ Full ❏ Partial ❏ None

c. Traffic Volume ❏ Low ❏ Moderate ❏ High

d. Operating Speed ❏ Low ❏ Moderate ❏ High

e. Task Complexity ❏ Simple ❏ Moderate ❏ Complex

f. Hazard(s) ❏ None ❏ One or Two ❏ Multiple

g . Hazard Visibility ❏ Good ❏ Fair ❏ Poor

h. Sight Distance ❏ Good ❏ Fair ❏ Poor

i. Expectancy Violations ❏ None ❏ Minor ❏ Major

j. Visual Clutter ❏ None ❏ Moderate ❏ High

k. Competing Information ❏ None ❏ One or Two Sources ❏ Many

l. Information Complexity ❏ Simple ❏ Moderate ❏ Complex

2. Rate overall information load:

❏ Very Low Information Load – Underload(This condition is very unlikely except for flat, straight roadways in open farm country)

❏ Low Information Load – Possible Underload(Look for incidence of single vehicle run off road accidents)

❏ Moderate Information Load

❏ High Information Load – Possible Overload(Look for incidence of intersection accidents in suburban and urban areas)

❏ Very High Information Load – Overload(This condition is likely to occur at or near major interchangeson high volume urban freeways)



Specifying Information Needs

This activity uses Checklist 5 to specify informationneeds. Information needs are specified analytically.Inputs are obtained from determinations of the site’sproblems, its hazards and their visibility,expectancies and expectancy violations, andinformation load. Additional input comes frominformation about the laws, rules, regulations, andpractices of the jurisdiction in which the problemsite is located.

The objective of this activity is to identify site-specific information needed to negotiate the sitesafely and efficiently. The following needs areidentified:

• Laws, Rules, Regulations, Practices

• Hazard Warning

• Advance Warning/Hazard Identification

• Safe Speed and Path

• Speed and Path Changes

• Hazard Visibility Enhancement

• Navigation/Route Guidance

• Advance Guide Signs

• Location

• Direction

• Destination

• Route Confirmation/Turns

• Other Needs

• Service

• Landmarks

• Traffic Generators

Table 9 shows information needs by informationhandling zones.

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Table 9 – Standard Information Needs by Zones



Checklist 5 – Information Needs Specification

Are there traffic laws and regulations information needs? ❏ Yes ❏ No

❏ Right of Way ________________________ ❏ Speed _____________________________

❏ Parking _____________________________ ❏ Pedestrian __________________________

❏ Other ______________________________________________________________________

Are there hazards/expectancy violations warning information needs? ❏ Yes ❏ No

❏ Alignment Change ___________________ ❏ Intersection _________________________

❏ Traffic Control Devices ________________ ❏ Converging Lanes ____________________

❏ Road Narrows _______________________ ❏ Changes in Design ___________________

❏ Grades _____________________________ ❏ Surface Condition ____________________

❏ Railroad Crossings ____________________ ❏ Entrances/Crossings _________________

❏ Other ______________________________________________________________________

Is hazard visibility poor? Are expectancies violated? Is sight distance restricted? ❏ Yes ❏ No

Advance hazard/expectancy violation warning information needs: _________________________

Is a safe speed and/or path apparent? ❏ Yes ❏ No

Safe Speed Needs _______________________ Safe Path Needs ________________________

Is speed or path change information needed? ❏ Yes ❏ No

Speed/Path Change Information Needs: ______________________________________________

Is hazard/expectancy violation detection enhancement needed? ❏ Yes ❏ No

Detection enhancement needs: _____________________________________________________

Is route guidance information needed? ❏ Yes ❏ No

❏ Route Marking _______________________ ❏ Intersection/Interchange ______________

❏ Destinations _________________________ ❏ Services ___________________________

Is advance information needed? ❏ Yes ❏ No

Specify other information needs, if any: _______________________________________________



Evaluating the Current Information System

The final diagnostic activity, the current informationsystem evaluation, uses Checklist 6 as an aid. Thecurrent information system is evaluated in terms of12 rating factors, using information from theprevious activities as input, and engineeringjudgement to make individual and overallinformation system evaluations.

The objective of this activity is to evaluate thesuitability of the overall existing information systemand each of its elements (traffic control devices,informal information carriers, sight lines, etc.) infulfilling information needs and overcomingproblems identified by all activities in the PositiveGuidance procedure. This determination is neededduring the improvement development phase toinsure that effective elements of the currentinformation system are retained, and unsatisfactoryones improved.

Questions associated with the following currentinformation system’s rating factors should beanswered:

Presence

Are there traffic control devices or other informationdisplays in place that satisfy each identifiedinformation need? If not, what needs are notsatisfied?

Location

If needed information carriers are in place, are theyproperly located (visible when needed and whererequired)? What are the nature of deficiencies (e.g.,too close, too much offset, etc.)?

OTM Compliance

Are standard devices used in accordance with theOTM? What nonstandard devices are used?

Expectancy Violations

Do expectancy violations exist? Are they caused bythe site’s information displays? Are violatedexpectancies adequately restructured by currentdisplays? If they exist and are not adequatelyrestructured, what are the source(s) of eachviolation?

Superfluous Displays

What displays are superfluous, and how can they bedealt with? Are there too many displays? Are anyinformation sources in place of either a very lowprimacy or unnecessary? Can they be spread oreliminated?

Field of View

Is current information located within a driver’s fieldof view? Is blockage possible? If deficiencies exist,what are they?

Target Value

Are devices conspicuous enough (day and night) togain a driver’s attention, particularly when there isvisual clutter? Are special attention-gainingtechniques (e.g., oversized signs, beacons, etc.)needed? What can be done?

Content

Is the information content of a display very high?Can it be reduced or simplified? How can content bereduced?



Checklist 6 — Current Information System Evaluation

1. Are any information needs unsatisfied? ❏ Yes ❏ No

If Yes, Specify: _________________________________________________________________

2. Are all information sources properly located? ❏ Yes ❏ No

If No, Specify: __________________________________________________________________

3. Do all traffic control devices comply with the OTM? ❏ Yes ❏ No

If No, Specify: __________________________________________________________________

4. Do any information sources violate driver expectancy? ❏ Yes ❏ No

If Yes, Specify: _________________________________________________________________

5. Are there locations of likely information overload? ❏ Yes ❏ No

If Yes, can some devices be moved or eliminated? ❏ Yes ❏ No

If Yes, Specify: _________________________________________________________________

6. Are all information sources visible from all driver eye positions? ❏ Yes ❏ No

If No, Specify:

7. Are any information sources too inconspicuous to be seen? ❏ Yes ❏ No

If Yes, can special emphasis techniques be used? _____________________________________

If Yes, Specify: _________________________________________________________________

8. Do any signs contain too much information to be read completely? ❏ Yes ❏ No

If Yes, Specify: _________________________________________________________________

Recommend improvement: _______________________________________________________

9. Are any signs inaccurate, confusing, ambiguous or unreadable? ❏ Yes ❏ No

If Yes, Specify: _________________________________________________________________



Accuracy

Is the displayed information accurate? Current?Credible? What inadequacies exist?

Understandability

Is the information displayed understandable tounfamiliar drivers? If not, why?

Ambiguity

Is the displayed information potentially ambiguous?Can it create confusion for unfamiliar drivers? Whatmakes it ambiguous?

Legibility

Is the information legible at the road’s operatingspeed to drivers with 20/40 vision? Is theresufficient contrast? Can it be read and acted on?What makes it illegible?

Developing Improvements

There is no formula procedure for improvementdevelopment except as province wide design andtraffic control device policies dictate. This is dueprimarily to the broad range and diversity ofproblems that occur, their site-specific nature, andthe wide spectrum of potential solutions.

As a beginning step in this phase, if there areunsatisfied information needs identified in Checklist6, it is appropriate to make a comprehensive list ofall current standard traffic control devices thataddress each specific need. However, it is importantto recognize that some needs are not addressed bytraffic control devices, and solutions to someproblems might not involve and/or might gobeyond improving the site’s information system withtraffic control devices. For example, positive

guidance can be achieved through reconstruction toremove hazards. Positive guidance can also beachieved by:

• Enhancing a hazard’s sight distance;

• Removing structures, foliage and berm;

• Painting curbs;

• Lighting crossings, crosswalks, interchanges, andfreeways; and

• Altering a site’s traffic operations through one-waystreets, commercial vehicle restrictions, and signaltiming changes.

However, in many cases, Positive Guidanceimprovements will involve optimizing the site’sinformation system through traffic control devices.

After the Positive Guidance procedure has beencompleted, potential devices, techniques, andstrategies that could be used to improve the site’ssafety and operating efficiency should be identifiedand assessed, and an improved information systemthat fulfills all information needs should bedeveloped. Consideration should be given toselecting devices that the procedure has identifiedas needed, and by applying the following selectionfactors.

Historical Effectiveness

MTO and other jurisdictions within the Province usea repertoire of techniques, devices, and strategiesthat have proven to be effective in past applications.It is generally proper to use these practices in similarapplications. All jurisdictions within the Provinceshould therefore use appropriate solutions withdemonstrated historical effectiveness whenapplicable.



Human Factors Considerations

Section 2 of this Appendix C contains humanfactors considerations that should be addressed indevice selection. These include basic conceptsabout the driver and the driving task, and sightdistance criteria.

Target Populations

When the procedure identifies the existence ofsignificant target populations (e.g., older drivers,non-english speaking drivers, truckers, motorcyclists,pedestrians), devices should be designed orselected that take their special needs or attributesinto account to the maximum extent possible.

OTM Effectiveness Criteria

The combined books of this Ontario Traffic Manualcomprise the Provincial standard governing thedesign and deployment of traffic control devices.Keep in mind five basic traffic control deviceselection criteria:

• Fulfill a need;

• Command attention;

• Convey a clear simple meaning;

• Command the respect of road users;

• Give adequate time for a proper response.

Standardization

Standard traffic control devices, specified in theOTM and consistently applied across the province,reduce ambiguity, and assure universalunderstanding. On the other hand, non-standarddevices and applications might result in confusion,since their meaning might not be readily apparent,particularly to unfamiliar drivers. Standardization

also facilitates the “self-learning” of new devices andapplications, since drivers will always be able to linksituations with device applications, thereby learningtheir meaning.

It is recognized that there are applications for whichno standard device exists, and that nonstandarddevices might be necessary. For example, there isno standard sign to alert drivers of upcominggrooved or milled pavement in a construction zone.In these instances, if a non-standard or experimentaldevice is developed, the device should be pretestedto assure that it is readily understood, adheres toOTM requirements, and employs sound humanfactors display criteria. Use of non-standard devicesshould be kept to a minimum, and when used, theireffectiveness should be evaluated.

Engineering/Economic Considerations

Engineering and economic considerations thataffect device selection and improvement designinclude costs, available funding, implementationtime frame, feasibility, device availability, installationrequirements, reliability, maintenance factors,service life, climate, etc. Many of theseconsiderations cannot be assessed until deviceshave been selected and display techniquesidentified. It might be necessary to performhighway engineering economy and trade-off studiesto finalize site improvements.

Information Display Techniques

It is beyond the scope of this Appendix C to discussthe range of standard and nonstandard trafficcontrol devices and display techniques available toimprove the site’s information system. Standarddevices specified in the OTM include fixed andvariable signing, marking and delineation,signalization, curbs, islands, gates, barricades, etc.Display techniques include verbal messages,symbols, shape and colour codes, flashing warninglights, painted markings, raised reflectorized



pavement markers, gates, lights, repetition andredundancy, overhead sign installations, oversizeddisplays, etc. There are also numerous nonstandardand state-of-the-art devices and techniques such asreal-time variable message signs, Highway AdvisoryRadio, and in-vehicle information and navigationsystems.

4. Case Studies

4.1 Introduction

This section illustrates the application of the PositiveGuidance procedures to supplement the systematicsafety review engineering studies and giveadditional insights into drivers’ problems such asexpectancy violations, and information handling.The following materials contains neither the detail ofa full case study nor full Positive Guidanceprocedures, however, a comprehensive discussion ofa case study is provided in the Training Packageassociated with the OTM Book 1, Appendix C.

The training package includes a case study of anurban intersection in the Region of Niagara, with anintention to introduce the methodology ofconducting a safety review applying the PositiveGuidance Procedures. The purpose of the safetyreview is to identify any operational deficienciesaffecting traffic and pedestrians safety, develop andevaluate potential mitigating measures to reducecollision risk. The study includes a safety-orientedbenefit-cost analysis to demonstrate the value of thefeasible countermeasures.

4.2 General Procedures

The Positive Guidance principles and systematicprocedures were followed to review the historicdata, conduct the office reviews, and site surveys.The data of roadway geometry, traffic volumes,collision history and traffic conflict characteristicswere reviewed accompanied by completingChecklist during the site investigation to generateand evaluate improvement options. The undertakensteps are summarized as follows:



Diagnosis of Deficiencies

(1) Data Collection and Office Review:Intersection turning movement, collisionhistory, geometric features, access points toadjacent land use developments, traffic controldevices, signs, etc.

(2) Site Investigations:Site survey, complete checklists for hazardidentification, hazard visibility assessment,expectancy violation, information loadanalysis, information needs specification, andcurrent information system evaluation, trafficconflict observations, and spot speedsurvey, etc.

Development of Countermeasures

(1) Development of potential countermeasuresbased on the identified deficiencies,understanding of the driving behaviour, andfeasible solutions.

(2) Estimation of expected safety benefits basedon Accident Modification Factors (AMF),previous experiences, research work, etc. Itshould be noted that the current calibratedAMFs are not very definitive to estimate theexpected reduction of the collisions, however,they are used to predict ranges of safetybenefits associated with the implementationof specific countermeasures. On-going andfuture research work can provide betterestimates to substitute the current ones.

Recommendations and Conclusion

Evaluation of recommended countermeasures andimprovements is based on the benefit-cost analysis.Costs are based on the cost of improvements andbenefits are expected savings in collisions.

4.3 Urban Intersection Case Study

Site Location

This is a case study of an urban intersection in theRegion of Niagara. The intersection is located in thesouth east section of the City of Niagara Falls,providing access to major nodes of attraction suchas Casino Niagara, the Falls, Museums, and MapleLeaf Village. The Region identified this intersectionas a deficient intersection which had high motorvehicle collision risk and safety concerns, andextensive land use activities.

The purpose of the study is to conduct a review oftraffic conditions and collision characteristics toidentify any operational deficiencies affecting trafficand pedestrians safety, and to develop and evaluatepotential mitigating measures to reduce collisionrisk. The study includes a safety-oriented benefit-cost analysis to demonstrate the value of thefeasible countermeasures.

The Positive Guidance principles and systematicprocedures were followed to review the historicdata, conduct the office review, and site surveys.The data of geometry, traffic volumes, collisionhistory and traffic conflict characteristics werereviewed accompanied by checklists for hazardidentification, hazard visibility assessment,expectancy violation, information load analysis,information needs specification, and currentinformation system evaluation. The undertakensteps are summarized as follows:

(1) The geometric review included the inspectionof the road cross section characteristics, landuse, parking restrictions, horizontal andvertical alignments, and intersection trafficcontrol devices at the intersection.



(2) Intersection turning movement data werecollected and the intersection capacity wasevaluated using the Highway CapacitySoftware, where a level of service is assignedto the intersection legs (varying from A to F).Levels of Service A and B indicate generallygood conditions with minimum traffic delays.Levels of Service C and D indicate averageconditions with acceptable delays. Levels ofService E and F indicate poor conditions withlong delays and potentially significantlyqueuing.

(3) Summaries and original police records ofmotor vehicle collisions reported in the threeyears from 1994 to 1996, were provided bythe Region. Collisions were segregated into12 types, using the information available in thepolice report and the police officer sketches.These types are categorized as crossing, left-turn opposing, left-turn crossing, rear-end,weaving, sideswipe, cyclists, pedestrian, fixedobjects, right-turn, and head-on.

(4) A review of collision characteristics wasconducted including temporal and spatialdistributions, collision types, and collisionseverity. Contributing causes to the motorvehicle collisions were reviewed and trendswere established.

(5) Site investigations were conducted by drive-through, and walk-through. A traffic conflictsurvey was conducted by field observations of32-person hours of traffic operation at theintersection. The purpose of this survey was togain further insight into the collision risk. Also,spot speed survey was performed near theintersection (30 m to 40 m from theintersection) to find out any evidence ofspeeding at this location.

(6) Findings and results were analysed, safety-related problems were identified at theintersection and mitigation strategies weredeveloped.

More details of summaries of the collected data,conducted analysis, completed checklists, trafficconflict analysis, and speed surveys, recommendedcountermeasures, and a safety oriented benefit-costanalysis to demonstrate the value of the feasiblecounter-measures, are included in the trainingpackage case study.

Enquiries regarding the purchase and distribution of this manual should be directed to:

Publications Ontario

880 Bay Street

Toronto, Ontario, Canada M7A 1N8

Phone: 416.326.5300

Toll Free: 800.668.9938

TTY: 800.268.7095

Fax: 613.566.2234

Website: www.publications.gov.on.ca

Appendix C - Positive Guidance Toolkit · 2008-10-06 · Positive Guidance is provided when that...

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