Conference Interactive Program
To view the 2013 Annual Meeting Interactive Program
TRB 90th Annual Meeting (January 23-27, 2011)
Advancements in Quantification of Highway Safety Performance
Jan 24 2011 2:30PM- 5:00PM
Marriott, Salon 2
Safety Performance Functions for Intersections in Virginia (11-0418)
ABSTRACT In recent years, significant effort and money have been invested through both research and implemented projects to enhance highway safety in Virginia; however, there is still substantial room for improvement in both crash frequency and severity. As available funds are limited it is crucial to carefully allocate resources for safety improvement projects to be able to achieve the maximum safety benefits and the best possible return on investment. In this study, safety performance functions (SPFs) for intersections in Virginia were developed for use in conjunction with SafetyAnalyst, which contains a set of computerized analytical tools developed by the Federal Highway Administration. Some of these tools can be used to identify and prioritize highway locations that have the highest potential for crash reduction and safety improvement (ITT Corporation SafetyAnalyst User’s Manual, 2008). A SPF is a mathematical relationship between frequency of crashes by severity and the most significant causal factors on a specific type of road. The SafetyAnalyst User’s Manual presents several SPFs for intersections, but they were developed using data from Minnesota. It has been suggested that each state should develop its own SPFs based on crash and traffic data from the state (Harwood et al, 2004), because the suggested Minnesota SPFs may not adequately represent the crash characteristics in all states. In this study, the SPFs were developed using the average annual daily traffic (AADT) as the most significant causal factor, imitating the SPFs currently suggested by SafetyAnalyst. The SPFs were developed for both total crashes and combined fatal plus injury crashes through generalized linear modeling (GLM), using negative binomial (NB) distribution. SPFs were also developed for urban and rural intersections separately. In order to account for the different topographies in Virginia, statewide SPFs as well as specific regional SPFs were developed for the Northern, Western and Eastern regions (Read 2009). Because of the data available, the types of intersections included in this study were, 4-leg signalized, 4-leg with stop control at the minor approaches, 3-leg signalized, and 3-leg s with stop control at the minor approaches. The scope of the study was limited to Virginia Department of Transportation (VDOT) maintained roads due to the data that could be obtained from the databases used. Statistical comparisons of the SPFs based on Minnesota data with those based on the Virginia data showed that the specific SPFs developed for Virginia fit the Virginia crash data better. The report recommends that the Virginia Department of Transportation (VDOT) uses the SPFs developed for Virginia as this will facilitate the identification of sites with a high potential for safety improvement, which, in turn, with the implementation of appropriate safety improvements, will result in a considerable reduction in crashes and their severity.
Garber, Nicholas J., University of Virginia
Rivera, Griselle , University of Virginia
Lim, In-Kyu , Virginia Department of Transportation
Transportation Research Board. 500 Fifth St. NW, Washington, D.C. 20001
Copyright © 2012. National Academy of Sciences. All Rights Reserved.