Vehicle Speeds in Work Zones: An

Objective and Subjective Analysis

Mojtaba Ale Mohammadi, PhD CandidateGhulam H. Bham, PhD

Civil, Architectural and Environmental EngineeringMissouri University of Science and Technology

DISCLAIMER

The contents of this report reflect the views of the authors, who are responsible for the facts and the accuracy of the information presented

herein.

This document is disseminated under the sponsorship of the Department of Transportation University Transportation Centers Program, in the

interest of information exchange. The U.S. Government assumes no liability for the contents

or use thereof.

OUTLINE

• Introduction• Data Collection Sites• Methodology• Results

–Objective Evaluation–Subjective Evaluation

• Conclusions and Recommendations

3

INTRODUCTION

• Posted speed limits alone do not reduce vehicle speed

• Drivers’ compliance reduces if speed limit is lowered by more than 10 mph or unreasonable speed limits

• Most commonly used speed limit reductions are 0, 5, 10, and 20 mph

• Different speed limits in work zones make enforcement difficult

4

OBJECTIVES

Objective evaluation: vehicle speeds and

drivers’ speed limit compliance

Drivers’ Assessment: drivers’ perception

of speed limit and their compliance

DOT Survey: work zone speed limit best

practices

5

DATA COLLECTION SITESWaynesvilleI-44 West Bound, Right lane closed, Mile Marker: 152.8August 13th, 2009 – Thursday3 hours of data from 5 to 8 pmWZ Posted Speed Limit 60 mphWork Activity: Pavement Reconstruction

RollaI-44 West Bound, Right lane closed, Mile Marker: 185October 2nd, 2009 – Thursday5 hours of data from 12:15 to 7 pmWZ Posted Speed Limit 60 mphWork activity: Pavement Rehabilitation Lane width reduced by tubular markers

6

Pacific (WB & EB)I-44, Left lane closed, Mile Marker: 253

June 9th, 16th, 24th, 2010 – Wednesday, Wednesday, Thursday

20 hours of data from 6 to 11 am WZ Posted Speed Limit: 50 mphWork Activity: Addition of a New LaneLane width reduced by pavement markingData was also collected with no lane closure

7

DATA COLLECTION SITES

CubaI-44, West Bound, left lane closed, Mile Marker: 202.6November 6th, 2009 – Thursday

5 hours from 11:30 to 4:30 pmWZ Posted Speed Limit 60 mphWork Activity: Rumble Striping

8

Work zone Lane closed Data WZ Speed limit Activity

Waynesville Right 3 hours 60 mph Pavement reconstruction

Rolla Right 5 hours 60 mph Pavement rehabilitation

Pacific (WB) Left 20 hours 50 mph Additional lane

Pacific (EB) Left 20 hours 50 mph Additional lane

Cuba Left 5 hours 60 mph Rumble striping

Summary of work zone data

DATA COLLECTION SITES

9

• Collected at gas stations near work zones

• Car and truck drivers surveyed: 118

• Actual speed versus posted speed limit

• Speed limit compliance of other drivers

• Effect of construction activity on their speed

• Preference for work zone signage

DRIVER SURVEY DATA

< 525%

5-1020%

10-2025%

> 2031%

DRIVER SURVEY

10

02468

1012141618

Age (years)

Fre

qu

ency

Passenger Car69%

RV1%

Single Unit2%

Single Trailer21%

Double Trailer

7%

Age distribution

Driving experience (years)Vehicle Composition

11

To identify common WZ practices of DOTS

• WZ speed management policies

• WZ activities that warrant a reduction in speed

limit

• Factors influence WZ speed limit

• Compliance levels

DOT SURVEY DATA

METHODOLOGYField Data Extraction

12

-Sites were videotaped using HD video cameras

-Autoscope system software used to extract vehicle free flow speeds (FFS)

-FFS based on 5-second headway

-FFS assumed to be normally distributed

-Drivers were surveyed using a questionnaire near the Rolla and Pacific sites

-DOTs were surveyed on their common practices related to work zone speed limits

METHODOLOGY

Autoscope software for extracting the vehicle speed 13

Speed detector Movement detectors

Count detector

METHODOLOGY o Difference in speed of cars and trucks

o The effect of construction activity on vehicles speed

o Effect of lane closure on vehicles (1-lane vs. 2-lane open)

o Evaluate speed limit compliance

14

RESULTS: OBJECTIVE EVALUATION

15

OBJECTIVE EVALUATION

16

Car Truck Car Truck Car Truck Car TruckWaynesville

WBRolla WB Pacific WB Pacific EB

SL= 60 mph SL= 50 mph

0

10

20

30

40

50

60

70

80

5.8 6.3

6.1 6.4 5.4 5.3 4.1 4.5

Standard Deviation Mean

Pe

rce

nta

ge

(%

)

*** Significant at 99% level of confidence

** Significant at 95% level of confidence

Characteristics of Vehicle Speed – During Construction

1.2

mph

2.6

mph

**

1.8

mph

***

2.0

mph

***

Difference in mean speeds

OBJECTIVE EVALUATION

17

^ One lane open = 1, Two lanes open = 2

*** Significant at 99% level of confidence; ** Significant at 95% level of confidence;

* Significant at 90% level of confidence

Car Truck Car Truck Car Truck Car Truck Car TruckWaynesville

WB Rolla WB Cuba WB Pacific WB Pacific EB

SL= 60 mph SL= 50 mph

0

10

20

30

40

50

60

70

80

7.0 7.5

7.16.4

4.7 4.96.6 6.7 5.4

4.1

Standard Deviation Mean

Pe

rce

nta

ge

(%

)

*** Significant at 99% level of confidence

3.0

mph

***

4.1

mph

***

2.2

mph

***

1.8

mph

***

3.9

mph

***

Characteristics of Vehicle Speed – During No-Construction

Difference in mean speeds

OBJECTIVE EVALUATION

18

Work Zone Site

Difference in Standard Deviation # (mph)

Difference in Mean # (mph)

Passenger Cars Trucks Passenger Cars Truck

s Waynesville WB 1.18 1.19 4.0 2.2

Rolla WB 0.96 0.01 4.5 3.0

Pacific WB 1.21 1.42 3.5 3.6

Pacific EB 1.32 -0.44 4.7 2.8

Effects of Construction Activity on Vehicle Speeds

# Difference = speed with no construction – speed with construction

Bold: Significant at 99% level of confidence

OBJECTIVE EVALUATION

19

Speed Limit Compliance – During Construction C

ar

Tru

ck

Car

Tru

ck

Car

Tru

ck

Car

Tru

ck

Waynesville WB Rolla WB Pacific WB Pacific EB

0

10

20

30

40

50

60

70

80

Above Speed Limit > 5 mph Above Speed Limit

Pe

rce

nta

ge

(%

)

*** Significant at 99% level of confidence; ** Significant at 95% level of confidence;

* Significant at 90% level of confidence

+2.11**+1.47*

-14.56***-11.85**

+9.11***

+1.78**

+6.78***

+1.38*

OBJECTIVE EVALUATION

20

Speed Limit Compliance – During No-Construction

*** Significant at 99% level of confidence; ** Significant at 95% level of confidence;

* Significant at 90% level of confidence

Car Truck Car Truck Car Truck Car Truck Car TruckWaynesville WB Rolla WB Cuba WB Pacific WB Pacific EB

0

10

20

30

40

50

60

70

80

90

100Above Speed Limit > 5 mph Above Speed Limit

Work Zones

Perc

en

tag

e (

%)

+9.74***

+4.5***

-7.13***

-10.16***

+8.85***

+1.43*

+1.43*

+8.91***

+30.50***

+9.63***

RESULTS:

SUBJECTIVE EVALUATION

21

DRIVER SURVEY

22

< 0.5

0.5-1

1-2

2-3

>3

0 20 40 60 80 100 120 140

1

13

26

37

23

14

32

36

18

12

8

80

How many miles in advance would you prefer to know about the presence of a work zone?

How many miles in advance would you like to see the “Lane Closed Ahead” sign?

How many miles in advance would you like to see the “Reduced Speed Limit” sign?

Percent

Mil

es

Drivers’ preference regarding location of WZ signs

23

DRIVER SURVEY

Right after the first "Lane Closed Ahead" sign

Before I see the work zone

After I see the work zone

Just before the taper0

10

20

30

40

50

60

Pe

rce

nta

ge

(%

)

Where drivers move out of the closed lane?

24

DRIVER SURVEY

Car Truck Car TruckPacific (50 mph) Rolla (60 mph)

Speed limit (mph)

0

20

40

60

80

100

6080

6484

4020

3616

Disagree Agree

Per

cen

t

Did other drivers follow the speed limit?

25

DRIVER SURVEY

Car Truck Car TruckPacific (50 mph) Rolla (60 mph)

Speed Limit (mph)

0

10

20

30

40

50

60

70

80

90

100

1020 14

16

38

53

21

84

48

20

48

5 712

5

>60

50-60

40-50

30-40

<30

Per

cen

t

Drivers' Speed (mph)

Drivers’ speed through the work zone

26

DRIVER SURVEY

car truck car truckPacific (50 mph) Rolla (60 mph)

Speed Limit (mph)

0

20

40

60

80

100

2 7

33

74

5

2029

40

60

26

38

27

7

21

5 7

70

65

60

55

50

45

Per

cen

t

Suggested Speed Limit (mph)

Speed limit suggested by drivers

DRIVER SURVEY

• 92% of total respondents indicated construction activity reduced their speed

• 80% found the work zone speed limit to be safe

• 60% of participants indicated travel delay

27

DOT SURVEY – WORK ZONE PRACTICES• Twenty seven states responded to the survey • Major factors in determining the speed limit:

– presence of workers, lane width, – roadway alignment, and type of activity

• Seventy percent indicated a maximum reduction of

10-mph • Static speed limit signs are most commonly used • Best strategy to increase compliance is use of law

enforcement • Regulatory signs found effective by 25% of the

respondents

28

CONCLUSIONS• Passenger cars speeds higher than trucks by 1-2 mph

• Construction activity significant effects speed – Passenger cars and trucks speeds reduce by 2-5 mph

• With no-work zone construction activity, or construction activity not close to the open lane– More than 10% drivers traveled higher than 10 mph

above the speed limit

• Low drivers’ compliance with static speed limit

• Reduced lane width using tubular markers significantly affected the speed of vehicles– Speed reduced 8 mph below the speed limit

29

CONCLUSIONS• Drivers agree that construction activity reduces

their speed

• Field data showed construction reduces speed

• When most drivers traveled below the speed limit – They overestimate the number of other drivers that

do not comply with the speed limit

• When most drivers traveled above the speed limit – They underestimate the number of other drivers

that do not comply with the speed limit

30

CONCLUSIONS

• Higher compliance if WZ speed limit are consistent with drivers expectation

• Drivers prefer well informed more than a mile ahead of WZ

31

RECOMMENDATIONS

• Vary WZ speed limits with varying levels of traffic congestion

• Use of variable speed limits for work zones with closed lanes and short-term construction activity periods

• To reduce speed, tubular markers than pavement markings for separating the closed lane (construction area) from the open lanes

32

ACKNOWLEDGEMENT

• The research grant from the Smart Work Zone Deployment Initiative (SWZDI) and Mid-America Transportation Center (MATC)

• Ms. Victoria Woods, Mr. Tim Hellebusch and their staff at the Missouri DOT in data collection

• Praveen Edara at University of Missouri at Columbia for sharing the DOT survey results

33

You can copy any of these graphics and paste them on other slides.

Slide design © 2009, Mid-America Transportation Center. All rights reserved.

Ghulam H. Bham, Ph.D.Civil, Architectural and Environmental Engineering

Missouri University of Science and TechnologyPhone (573) 341-6286

Fax (573) 341-4729 Email: ghbham@mst.edu

CREDITS