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 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 Multilane Highway and Freeway Segments Maintained by the Virginia Department of Transportation
Development of Safety Performance Functions for Multilane Highway and Freeway Segments 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 Multilane Highway and Freeway Segments Maintained by the Virginia Department of Transportation write by Young-Jun Kweon. This book was released on 2014. Development of Safety Performance Functions for Multilane Highway and Freeway Segments Maintained by the Virginia Department of Transportation available in PDF, EPUB and Kindle. The Virginia Department of Transportation (VDOT) adopted the software Safety Analyst as its highway safety management tool in 2009. One of the requirements for implementation of Safety Analyst is to have appropriate safety performance functions (SPFs) reflecting Virginia conditions. The purpose of this study was to develop such SPFs for multilane highway and freeway segments that could replace Safety Analyst's default SPFs. Five years (2004-2008) of data collected from 20,235 multilane highway segments and 2,905 directional freeway segments in Virginia were used in the development of the SPFs. Statewide SPFs were developed for 4 subtypes of multilane highway segments and 10 subtypes of freeway segments. VDOT district-group SPFs were developed for 4 subtypes of multilane highway segments. The default SPFs in Safety Analyst were found to be different than the developed Virginia SPFs with respect to their curve shapes, and, as a result, adjusting the default SPFs to Virginia conditions by calibration factors resulted in inaccurate crash predictions at low and high volumes of annual average daily traffic. Thus, the Virginia-specific statewide SPFs developed in this study should be used when implementing Safety Analyst in Virginia. Although the shapes of the multilane highway segment SPFs were found to vary across VDOT districts, incorporating variations through the creation of new subtypes was found to be inappropriate for the current version of Safety Analyst. As a consequence, district-group SPFs for the multilane highway segments cannot be implemented in Safety Analyst. However, all SPFs developed in this study, including district group SPFs, can be implemented without the use of Safety Analyst. Therefore, use of the statewide SPFs developed in this study is recommended when Safety Analyst can be used and use of the statewide or district-group SPFs developed in this study is recommended when implementation of Safety Analyst is not feasible.
Development of Safety Performance Functions for Two-lane Roads in Virginia
Development of Safety Performance Functions for Two-lane 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 Safety Performance Functions for Two-lane Roads in Virginia write by Phillip R. Haas. This book was released on 2009. Development of Safety Performance Functions for Two-lane Roads in Virginia available in PDF, EPUB and Kindle.
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.
