Transportation Impact Analysis

Presented By

Katy Flynn, P.E.

Fehr & Peers

February 19, 2008

Presentation Overview

• What is a Transportation Impact Analysis?• Why do we prepare Transportation Impact

Analyses?• How do we prepare a Transportation Impact

Analysis?

What is a Transportation Impact Analysis (TIA)?

A Transportation Impact Analysis evaluates

the impacts of a proposed project on the surrounding transportation system

and identifies measures to mitigate significant impacts.

Why Do We Prepare TIAs?• Evaluate Project Impacts • Agency Requirements

• Criteria – Project meets a trip threshold (for Washoe County the Threshold is 80 or more trips during the peak hour or 750 or more on a daily basis), controversial project, nearby intersections that operate at a poor level of service, safety issues

• Evaluate Land Use/Development Options• Environmental Laws

• NEPA (National Environmental Policy Act)• CEQA (California Environmental Quality Act)

• Assess Impact Fees

How do we prepare a TIA? – Getting Started

Determining if a TIA is required? • Obtain Site Plan (Get involved in site plan development)• Evaluate Criteria

Scoping Process• Talk to jurisdiction/agency staff• Determine:

› Study Area

› Analysis Time Periods (AM Peak, PM Peak, etc.)

› Analysis Scenarios (Existing, Background, Project, Cumulative, Phasing, Alternatives)

› LOS Calculation Methods (2000 HCM, Circular 212)

› Significance Criteria (LOS Thresholds, Left-turn Queues, Neighborhood Issues, Neighborhood Intrusion, Safety Issues)

How do we prepare a TIA? – Site Reconnaissance & Data Collection

• Visit the Site to Collect: • Lane configurations• Traffic control devices• Speed limits• Turn lane lengths • Transit stops• Pedestrian facilities

• Observe study period conditions• Data collection:

• Turning movement intersection counts

• ADT• Vehicle classification• Accident history

How do we prepare a TIA? – Analysis• Determine the appropriate tool for the analysis: Isolated

intersection analysis vs. micro-simulation

How do we prepare a TIA? – Project Trip Generation

• Published Rates (ITE, RTC, Caltrans), surveys

• Factors that affect vehicle trip generation: Pass-By trips,

Internalization, transit, and others.

1991

1997

2003

How do we prepare a TIA? – Project Trip Distribution

• Existing Travel Patterns

• Complementary Land Uses (i.e. Residential and Office Uses)• Zip Code Data• Census Data• Travel Demand Model• Engineering Judgment

How do we prepare a TIA? – Project Conditions Analysis

• Add project traffic to existing conditions• Analyze LOS, Queuing, Impacts to transit/pedestrian facilities/bicycle facilities, etc.• Determine Impacts • Recommend mitigation measures…

How do we prepare a TIA? – Project Conditions Analysis – Mitigation Measures

• Traffic Signals• Signal Warrants

• Lane Additions• Access Modifications/

Access Management• Changes to Project Description• Left-Turn Restrictions• Roundabouts• Roadway Widening• Traffic Signal Coordination • Transportation Demand Management Programs• Impact Fees

How do we prepare a TIA? – Cumulative Conditions/Future Year Analysis

• 20 to 30 year horizon • Typically a planning level analysis – roadway

segment• Determine future traffic volumes

• Travel Demand Model • Growth Rate • Historical Data• Known long term projects• General Plan documents

How do we prepare a TIA? – Site Access

Private Driveway Design Criteria • Location/Spacing • Permitted Turning Movements • Signalization• Width• Offsets• Grade• Emergency Vehicle Access• Sight Distance

How do we prepare a TIA? – Site Circulation

Throat Depth Requirements

Source: Access Management Manual (TRB)

Source: Transportation and Land Development (ITE)

Driveway WidthSource: NDOT Access Management System and Standards, 1999

How do we prepare a TIA? – Site Circulation

• Drive Aisle Width • Dead-End Drive Aisles• Pedestrian Conflicts• Parking Supply vs. Demand• Truck Delivery Movements

How do we prepare a TIA? – Site Circulation

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