Transportation safety planning working group analysis tools march 27 28 2006
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Transportation Safety Planning Working Group “Analysis Tools” March 27-28, 2006. Dr. Simon Washington, Professor Department of Civil & Environmental Engineering, Ira A. Fulton School of Engineering Arizona State University. Acknowledgements.

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Transportation safety planning working group analysis tools march 27 28 2006

Transportation Safety Planning Working Group“Analysis Tools”March 27-28, 2006

Dr. Simon Washington, Professor

Department of Civil & Environmental Engineering, Ira A. Fulton School of Engineering

Arizona State University


  • The majority of the research describe here was paid for by NCHRP (8-44).

  • Participants in 8-44 included:

    Dr. Michael Meyer

    Dr. Eric Dumbaugh

    Ms. Ida van Schalkwyk

    Mr. Matthew Zoll

    Ms. Sudeshna Mitra

    Ms. Ashley Chang

Presentation overview
Presentation Overview

  • Background: Planning-level Safety Forecasting (PLANSAF)

  • Justification for PLANSAF models

  • General Modeling Approach

  • PLANSAF Examples

  • NCHRP 8-44-2 Objectives

  • Research Tasks

Background need for plansaf models
Background: Need for PLANSAF Models

  • Setting safety targets

    • Establish reasonable targets for fatal, injury, pedestrian, etc.

  • Predict safety impacts of large-scale projects

    • Safety impacts of future population, schools, transportation infrastructure

  • Compare and contrast growth scenarios

    • Infill vs. sprawl, interstate vs. expressways, etc.

  • Examine safety impact of region-wide policies/programs

    • Implementing region-wide photo-enforcement for red light running, etc.

  • Support PROACTIVE safety planning

Background planning level safety forecasting
Background: Planning-level Safety Forecasting

  • NCHRP 8-44 completed fall 2005

  • It resulted in a Manual for MPOs and DOTs on how to incorporate safety into long-range transportation planning

  • It also identified software and analysis tools available……….

  • And significant GAPS in software/tools…….

Background macroscopic vs microscopic safety models
Background: Macroscopic vs. microscopic safety models

  • PLANSAF models differ from microscopic models in that:

    • They should not be used to guide selection of microscopic safety investments

    • Input data are aggregate and not site specific (TAZ is smallest unit of analysis)

    • Focus is prediction NOT explanation

    • They should be used to inform corridor or region-wide alternatives comparisons

Justification for plansaf taz level models
Justification for PLANSAF (TAZ level) models

  • Crashes are largely random events…

    • 90%+ human error: distractions, speeding, following too closely

  • Aggregate safety differences substantiated….

    • Young and elderly drivers; minorities/males and safety restraints; intersections vs. segments; high vs. low speeds; urban vs. rural; facility design levels; etc.

  • Models for prediction have fewer restrictions than models for explanation…..

    • Inference, or effects of isolated variables (estimated coefficients) not too important, multicollinearity tolerated; goodness of fit and predictive ability most important

Plansafe core methodology
PLANSAFE Core Methodology

  • Model Calibration: Using local/regional data, calibrate safety forecasting models to predict baseline conditions

  • Define analysis area and supporting data: Define investment/growth scenarios: corridor, sub-regional, regional

  • Run future baseline forecast: Forecast future safety for growth scenario

  • Select safety investment alternatives: Which safety investments will be made?

  • Provide output for decision-makers: Will include estimated effects and uncertainty

Simple example 10 taz forecast of incapacitating fatal injuries
Simple Example: 10 TAZ forecast of Incapacitating & Fatal Injuries

A corridor improvement is being considered that will bring about new residential and commercial development to 10 TAZs, as well as increased population and resultant traffic volumes. A host of new intersections will be added because of the project, as well as new road mileage.

Interest focuses on what changes to safety are anticipated as result of this project.

Safety forecast results
Safety Forecast Results: Injuries

As a result of the proposed project there is an anticipated increase in serious incapacitating injuries and fatalities from 68 to 87, or 19 additional crashes (new population, new roads, etc.)

If a 20% reduction in these crash types was desired (a Plan Target), then 87(.80) = 69 crashes is the future safety target.

Safety investments would need to identified to reduce crashes from 87 to 69 (a reduction of 18 crashes)

NOTE: Overall crashes have increased (from 68 to 69) even though safety improvements are made!

Nchrp 8 44 2 objectives
NCHRP 8-44-2 Objectives Injuries

  • To develop a robust, defensible, and accurate analytical set of algorithms to forecast the safety impacts of engineering and behavioral countermeasure investments at the planning-level

  • To develop user-friendly software, compatible to the extent possible with planning-level data inputs, to incorporate the analytical procedures for forecasting safety

  • To develop guidance materials to accompany the analytical procedures and software

Nchrp 8 44 2
NCHRP 8-44-2 Injuries

Transportation Safety Planning: Forecasting the Safety Impacts of Socio-Demographic Changes and Safety Countermeasures

Will continue/expand work started during NCHRP 8-44

Start: Spring 06

End: Fall 08