Development of a Systemic Safety Improvement Plan for Two-Lane Rural Roads 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 a Systemic Safety Improvement Plan for Two-Lane Rural Roads in Virginia write by Hyun W. Cho. This book was released on 2020. Development of a Systemic Safety Improvement Plan for Two-Lane Rural Roads in Virginia available in PDF, EPUB and Kindle. About 17,500 crashes per year occur on the more than 32,800 lane-miles of undivided two-lane rural roads maintained by the Virginia Department of Transportation (VDOT), and crash numbers are increasing. Roadway departure (RD) crashes comprise about 58% of crashes on these roads. Since these crashes are widely distributed across the state, determining how and where to focus limited highway safety resources through the deployment of low-cost, high-benefit systemic countermeasures is paramount to beginning to reduce the number of crashes on these roads. This purpose of this study was to develop a systemic safety improvement plan for RD crashes on two-lane rural roads using low-cost countermeasures. Segments that have the potential for safety improvement were selected using VDOT’s RD safety performance functions. Decision tree analysis was applied to perform a systemic classification of roadway characteristics that are correlated with RD problems. A list of countermeasures to deploy to target specific segments and patterns was developed based on the literature and input from VDOT staff. The countermeasures were intended to warn of curves ahead, delineate curves, and warn of lane/road departure. Before deployment, a study of the section by VDOT district traffic engineering staff is planned in order to finalize the safety improvement plan. The output of the study will be a safety improvement plan to deploy treatments systemically to two-lane rural roads as part of VDOT’s safety program.
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.
Systemic Low-Cost Countermeasures for an Unsignalized Intersection Safety Improvement Plan for Virginia
Systemic Low-Cost Countermeasures for an Unsignalized Intersection Safety Improvement Plan for 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 Systemic Low-Cost Countermeasures for an Unsignalized Intersection Safety Improvement Plan for Virginia write by Cottrell, Jr. (Benjamin H.). This book was released on 2018. Systemic Low-Cost Countermeasures for an Unsignalized Intersection Safety Improvement Plan for Virginia available in PDF, EPUB and Kindle. With more than 80,000 unsignalized intersections in Virginia, determining how and where to focus limited highway safety resources through deployment of low-cost, high-benefit systemic countermeasures is paramount to beginning to reduce the number of fatal and injury crashes at unsignalized intersections in Virginia. The purpose of this study was to develop a safety improvement plan for unsignalized intersections using systemic low-cost countermeasures. The scope of the study focused on unsignalized intersections with stop sign control on the minor approaches. Virginia’s unsignalized intersection crashes over a 5-year period were assessed to determine predominant crash trends and crash types to target for treatment. Three Virginia Department of Transportation (VDOT) databases (crashes, roadway inventory, and traffic counts) were combined for unsignalized intersections. Four focus collision types with the highest frequency of crashes and the greatest potential reduction in crashes were identified from the data: 3-leg angle, 3-leg fixed object off road, 4-leg angle, and 4-leg rear-end. Chi-square automatic interaction detection (CHAID) was used to perform a systemic analysis to identify a group of intersections based on independent variables (roadway inventory and traffic count variables) that were most strongly related to the focus collision types. After the crash assessment was performed, case studies of selected intersections in each group were reviewed to assess the factors that might influence the four focus collision types. A tiered list of countermeasures to deploy was developed based on the literature and input from VDOT staff. The countermeasures were intended to warn of the stop ahead, to make the stop sign and stop location more visible on the minor street, and to warn of the intersection ahead on the major street. The potential for safety improvement measure was used to prioritize the candidate treatment intersections. Before deployment, a study of the intersections conducted by district traffic engineering staff is planned in order to finalize the safety improvement plan. The output of the study is a safety improvement plan to deploy treatments to unsignalized intersections systemically as part of the safety program. The plan can be adjusted based on available funding.
A Planning-level Methodology for Identifying High-crash Sections of Virginia's Primary System
A Planning-level Methodology for Identifying High-crash Sections of Virginia's Primary System - 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 A Planning-level Methodology for Identifying High-crash Sections of Virginia's Primary System write by Ajmal Hamidi. This book was released on 2010. A Planning-level Methodology for Identifying High-crash Sections of Virginia's Primary System available in PDF, EPUB and Kindle. The Virginia Department of Transportation (VDOT) has been developing safety performance functions (SPFs) as a way to identify sites with a potential for safety improvement more effectively. An SPF estimates the expected safety performance of a roadway as a function of its characteristics. Using SPFs, VDOT can identify which roads have a significantly higher number of crashes than would be expected based on site conditions. Other VDOT studies have developed SPFs with a microscopic perspective that separately examine individual intersections or discrete roadway segments. The purpose of this study was to develop an SPF-based methodology to conduct more intermediate-scale safety analyses. VDOT's Traffic Engineering Division indicated that such a methodology would be useful for corridor screening and planning-level applications. The scope of the study was limited to the following roadway types in Virginia's primary system: rural two-lane, rural multilane divided, rural multilane undivided, urban two-lane, urban multilane divided, and urban multilane undivided. For each type, roadway inventory data, traffic volume data, and crash data from 2003 through 2007 were compiled and integrated into a database. This study then took an approach that diverged from that of other SPF research to develop intermediate-scale SPFs. Instead of crashes at intersections and on roadway segments being separated, intersection and segment crashes were combined and mapped onto the appropriate roadway inventory links. In addition, site aggregation was performed to combine similar, adjacent roadway links into longer aggregated sites. SPFs were then generated from these aggregated sites through regression analysis. A site prioritization demonstration was then performed using the aggregate SPFs and aggregate sites to create lists of sites with the highest potential for safety improvement. Finally, a comparison of these lists and those generated by the critical rate method produced quantitative evidence of the advantage of the developed SPF-based methodology over the traditionally used critical rate method. Once implemented, the methodology developed in this study should enable VDOT to conduct corridor screening and planning-level analyses in a more effective and cost-efficient manner.
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.
