Safety Performance Functions for Intersections on Highways Maintained by the Virginia Department of Transportation - read free eBook in online reader or directly download on the web page. Select files or add your book in reader. Download and read online ebook Safety Performance Functions for Intersections on Highways Maintained by the Virginia Department of Transportation write by Nicholas J. Garber. This book was released on 2010. Safety Performance Functions for Intersections on Highways Maintained by the Virginia Department of Transportation available in PDF, EPUB and Kindle. In recent years, significant effort and money have been invested through research and implemented safety projects to enhance highway safety in Virginia. However, there is still substantial room for improvement in both crash frequency and severity. As there are limits in the available funds for safety improvements, it is crucial that allocated resources for safety improvement be spent at highway locations that will result in the maximum safety benefits. In addition, intersection crashes play a significant role in the safety conditions in Virginia. For example, crashes at intersections in Virginia for the period 2003 through 2007 account for 43.8% of all crashes and 26% of fatal crashes. Therefore, identifying intersections for safety improvements that will give the highest potential for crash reduction when appropriate safety countermeasures are implemented will have a significant impact on the overall safety performance of roads in Virginia. The Federal Highway Administration (FHWA) has developed a procedure for identifying highway locations that have the highest potential for crash reduction (ITT Corporation, 2008). A critical component of this method is the use of safety performance functions (SPFs) to determine the potential for crash reductions at a location. An SPF is a mathematical relationship (model) between frequency of crashes by severity and the most significant causal factors on a specific highway. Although the SafetyAnalyst User's Manual presents several SPFs for intersections, these were developed using data from Minnesota. FHWA also suggested that if feasible, each state should develop its own SPFs based on crash and traffic volume data from the state, as the SPFs that are based on Minnesota data may not adequately represent the crash characteristics in all states. SPFs for intersections in Virginia were developed using the annual average daily traffic as the most significant causal factor, emulating the SPFs currently suggested by SafetyAnalyst. The SPFs were developed for both total crashes and combined fatal plus injury crashes through generalized linear modeling using a negative binomial distribution. Models were also developed for urban and rural intersections separately, and in order to account for the different topographies in Virginia, SPFs were also developed for three regions: Northern, Western, and Eastern. This report covers Phases I and II of the study, which includes urban and rural intersections maintained by VDOT. Statistical comparisons of the models based on Minnesota data with those based on the Virginia data showed that the specific models developed for Virginia fit the Virginia crash data better. The report recommends that VDOT's Traffic Engineering Division use the SPFs developed for Virginia and the specific regional SPFs suggested in this report to prioritize the locations in need of safety improvement.
Development of Safety Performance Functions for Intersections in Virginia
Development of Safety Performance Functions for Intersections in Virginia - read free eBook in online reader or directly download on the web page. Select files or add your book in reader. Download and read online ebook Development of Safety Performance Functions for Intersections in Virginia write by Griselle Rivera. This book was released on 2010. Development of Safety Performance Functions for Intersections in Virginia available in PDF, EPUB and Kindle.
Development of Safety Performance Functions for Two-lane Roads Maintained by the Virginia Department of Transportation
Development of Safety Performance Functions for Two-lane Roads Maintained by the Virginia Department of Transportation - read free eBook in online reader or directly download on the web page. Select files or add your book in reader. Download and read online ebook Development of Safety Performance Functions for Two-lane Roads Maintained by the Virginia Department of Transportation write by Nicholas J. Garber. This book was released on 2010. Development of Safety Performance Functions for Two-lane Roads Maintained by the Virginia Department of Transportation available in PDF, EPUB and Kindle. In recent years, significant effort and money have been invested to enhance highway safety. As available funds decrease, the allocation of resources for safety improvement projects must yield the maximum possible return on investment. Identifying highway locations that have the highest potential for crash reduction with the implementation of effective safety countermeasures is therefore an important first step in achieving the maximum return on safety investment. This study was undertaken to develop safety performance functions (SPFs) for use in Virginia in conjunction with SafetyAnalyst, a computerized analytical tool that can be used for prioritizing safety projects. A safety performance function is a mathematical relationship (model) between frequency of crashes by severity and the most significant causal factors of crashes for a specific type of road. Although the SafetyAnalyst User's Manual recommends four SPFs for two-lane segments, these SPFs were developed using data from Ohio. Because the transferability of these SPFs to other states could not be guaranteed by the developers of the four recommended SPFs, it is necessary to calibrate or develop valid SPFs for each state using appropriate data from the state. In this study, annual average daily traffic (AADT) was used as the most significant causal factor for crashes, emulating the SPFs currently suggested by Safety Analyst. SPFs for two-lane roads in Virginia were developed for total crashes and combined fatal plus injury crashes through generalized linear modeling using a negative binomial distribution for the crashes. Models were developed for urban and rural areas separately, and in order to account for the different topographies in Virginia, SPFs were also separately developed for three regions in Virginia. A total of 139,635 sites were identified for use in this study. Each site is a segment of a rural or urban two-lane road without an intersection for which AADT data were available for the years 2003 through 2007 inclusive and no change in facility type had occurred over that period. A comparative analysis based on the Freeman-Tukey R2 coefficient was then conducted between the relevant Ohio SPFs suggested for use in the SafetyAnalyst User's Manual and those specifically developed in this study for Virginia to determine which set of models better fit the Virginia data. In general, the results indicated that the SPFs specifically developed for Virginia fit the Virginia data better. The final step in this methodology was to illustrate the value of SPFs developed through an analysis of sample sites and the need of the sites for safety improvement based on SPFs as compared to crash rates. The results indicated that prioritization using the empirical Bayes method that incorporates the SPFs resulted in a higher potential for reduction in crashes than did prioritization using crash rates. The effective use of SafetyAnalyst 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.
Development of Safety Performance Functions for Network Screening of Roadway Departure Crashes in Virginia
Development of Safety Performance Functions for Network Screening of Roadway Departure Crashes in Virginia - read free eBook in online reader or directly download on the web page. Select files or add your book in reader. Download and read online ebook Development of Safety Performance Functions for Network Screening of Roadway Departure Crashes in Virginia write by Young-Jun Kweon. This book was released on 2019. Development of Safety Performance Functions for Network Screening of Roadway Departure Crashes in Virginia available in PDF, EPUB and Kindle. Roadway departure (RD) is recognized as one of the eight emphasis areas in the Virginia 2017-2021 Strategic Highway Safety Plan (SHSP), and the Virginia Department of Transportation (VDOT) currently uses counts of RD crashes to identify locations for RD safety improvement. However, identifying locations based on crash counts is subject to bias and inaccuracy, leading to ineffective or erroneous outcomes. The safety performance functions (SPFs) VDOT has been using for statewide network screening might be used for RD safety improvement, but this could lead to undesirable outcomes in that the current SPFs focus on all crash types and RD safety issues are believed to be different from those of other crash types. This study was designed to develop SPFs for statewide network screening for RD safety improvements to overcome this issue. RD SPFs were developed for 16 site types ranging from rural 2-lane segments to urban freeway segments with 8 or more lanes. It should be noted that crashes within 250 feet from an intersection are excluded according to VDOT’s RD definition. Of the 96 RD SPFs (16 site types x 2 severity levels x 3 functional forms) initially investigated, 93 RD SPFs were successfully developed for RD network screening. One site type did not result in statistically significant RD SPFs for fatal and injury crashes, likely because of its small sample size. The study found that the RD SPFs vary in their functional forms of annual average daily traffic (AADT) across the site types. The logarithmic functional form of AADT, regarded as a standard for an SPF, is deemed suitable in general for a typical range of AADT. However, that form could be severely deviated from the true relationship in the data. The study also found that the functional forms of AADT vary by injury severity. The forms are generally similar between the two severity levels, yet there are some cases where the difference is substantial. Accordingly, the functional form of AADT in an SPF for RD crashes should be determined for each site type and by severity level (all RD crashes and fatal and injury RD crashes) separately whenever possible. Based on the findings, the study recommends that the RD SPFs developed in this study be incorporated in the current VDOT statewide network RD screening procedure. Specifically, the final RD SPFs determined by goodness of fit and prediction capability measures (Tables 11 and 12) are recommended for use. For some site types, more than one final SPF are provided, allowing VDOT to select the most appropriate one for network screening considering the practicality of implementing the RD SPFs. Development of separate SPFs by site type and by severity was desirable to avoid possible inaccurate outcomes of network screening.
Development of a Safety Evaluation Procedure for Identifying High-risk Signalized Intersections in the Virginia Department of Transportation's Northern Virginia District
Development of a Safety Evaluation Procedure for Identifying High-risk Signalized Intersections in the Virginia Department of Transportation's Northern Virginia District - read free eBook in online reader or directly download on the web page. Select files or add your book in reader. Download and read online ebook Development of a Safety Evaluation Procedure for Identifying High-risk Signalized Intersections in the Virginia Department of Transportation's Northern Virginia District write by Young-Jun Kweon. This book was released on 2007. Development of a Safety Evaluation Procedure for Identifying High-risk Signalized Intersections in the Virginia Department of Transportation's Northern Virginia District available in PDF, EPUB and Kindle. This research was undertaken to develop an evaluation procedure to identify high-risk four-legged signalized intersections in VDOT's Northern Virginia district by traffic movements and times of day. By using the developed procedure, traffic engineers are expected to be able to identify signalized intersections where the traffic crash occurrences under different traffic conditions for different times of day are more frequent than would normally be expected. Using generalized linear models such as negative binomial models, one safety performance function was estimated for each of nine crash population reference groups formed by three traffic crash patterns (crash patterns 1, 4, and 6) and four times of day (A.M. peak, mid day, P.M. peak, and evening off peak). Crash pattern 1 is a same-direction crash (rear-end, sideswipe or angle crash) that occurs after exiting the intersection; crash pattern 4 is a right-angle crash between two adjacent straight-through vehicle movements in the intersection; and crash pattern 6 is an angle or head-on or opposite sideswipe crash between a straight-through vehicle movement and an opposing left-turn vehicle movement in the intersection. The procedure developed in this study is based on the empirical Bayes (EB) method. Additional data do not need to be collected in order to use the EB procedure because all the data required for applying the EB procedure should be obtainable from VDOT's crash database and from Synchro input data that are already available to traffic engineers for traffic signal phase plans. Thus, the EB procedure is cost-effective and readily applicable. For easy application of the EB procedure, an EB spreadsheet was developed using Microsoft Excel, and a users' guide was prepared. These are available from the author upon request.
