Two Lane Rural Highways Safety Performance Functions
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Two Lane Rural Highways Safety Performance Functions
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Author : Venky Shankar
language : en
Publisher:
Release Date : 2016
Two Lane Rural Highways Safety Performance Functions written by Venky Shankar and has been published by this book supported file pdf, txt, epub, kindle and other format this book has been release on 2016 with Roads categories.
Development Of Safety Performance Functions For Two Lane Rural Highways In The State Of Ohio
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Author : Abdulrahman Khalid Faden
language : en
Publisher:
Release Date : 2020
Development Of Safety Performance Functions For Two Lane Rural Highways In The State Of Ohio written by Abdulrahman Khalid Faden and has been published by this book supported file pdf, txt, epub, kindle and other format this book has been release on 2020 with categories.
The Highway Safety Manual (HSM), which is the guidance document for state departments of transportation (DOTs), was published in 2010, and one of its sections, called Part C of HSM, it involves the development of crash prediction methods. The goal of the predictive method is to develop and calibrate safety performance functions (SPFs). SPFs are mostly regression models that associate the expected number of crashes quantitatively with traffic exposure and geometric characteristics of the road. However, HSM's default prediction models are not suitable for all states or jurisdictions because each state and jurisdiction have different characteristics, such as terrain, driver behaviors, weather conditions, etc. Hence, the principal objective of this study is to develop a prediction method for producing Ohio-specific SPF models to use for rural two-lane highways in the state of Ohio. This study aims to create jurisdiction-specific SPFs for two-lane rural highway segments as the first study for this type of roadway facility in the state of Ohio. Highway geometric data for almost 40,067 segments that have 21,666.03 miles and 79,481 total crashes that occurred for 4 consecutive years (2012-2015) were obtained from the Highway Safety Information System (HSIS) to create these new models using negative binomial regression and the pruned forward selection method by adding the interaction terms via JMP Pro software. The most critical variables used for analyzing and creating the best models for the state of Ohio are average annual daily traffic (AADT), segment length, lane width, shoulder width, posted speed limit, presence of curves and grades, which were proven to be statistically significant in developing SPFs. Besides, the standard goodness-of-fit parameters were chosen to evaluate the regression models was AIC. Two models were created for rural two-lane, two-way road segments in the state of Ohio, which can be used to predict all crash types and fatal and injury crashes.
Applying Safety And Operational Effects Of Highway Design Features To Two Lane Rural Highways
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Author :
language : en
Publisher:
Release Date : 2003
Applying Safety And Operational Effects Of Highway Design Features To Two Lane Rural Highways written by and has been published by this book supported file pdf, txt, epub, kindle and other format this book has been release on 2003 with categories.
Rural two-lane highways constitute a majority of the mileage of public roads in the United States. Rural two-lane highways have 40% of the total travel but experience 60% of the highway fatalities. During the 1980's and 1990's, research was carried out in the United States to quantify the safety and operational effects of various key geometric design features including: lane and shoulder widths; roadside safety; horizontal and vertical alignment; sight distance; rural intersections. Aggregating this research has resulted in a compendium of the safety benefits of certain geometric design features for two-lane rural highways which links design standards and safety. This aggregated research information provides a basis for software analysis of proposed highway designs to assess their expected safety performance as well as the traditional capacity performance. Application of these benefits and effects achieves a numerical methodology for safety in a similar manner as is commonly carried out for capacity. This compendium of the safety and operational benefits of highway design features is being deployed in the United States to state highway departments in advance of the release of the software based analysis system. For the covering abstract of this conference see ITRD number E211395.
Development Of Safety Performance Functions For Two Lane Roads Maintained By The Virginia Department Of Transportation
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Author : Nicholas J. Garber
language : en
Publisher:
Release Date : 2010
Development Of Safety Performance Functions For Two Lane Roads Maintained By The Virginia Department Of Transportation written by Nicholas J. Garber and has been published by this book supported file pdf, txt, epub, kindle and other format this book has been release on 2010 with Roads categories.
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.
Highway Safety Manual
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Author :
language : en
Publisher: AASHTO
Release Date : 2010
Highway Safety Manual written by and has been published by AASHTO this book supported file pdf, txt, epub, kindle and other format this book has been release on 2010 with Technology & Engineering categories.
"The Highway Safety Manual (HSM) is a resource that provides safety knowledge and tools in a useful form to facilitate improved decision making based on safety performance. The focus of the HSM is to provide quantitative information for decision making. The HSM assembles currently available information and methodologies on measuring, estimating and evaluating roadways in terms of crash frequency (number of crashes per year) and crash severity (level of injuries due to crashes). The HSM presents tools and methodologies for consideration of 'safety' across the range of highway activities: planning, programming, project development, construction, operations, and maintenance. The purpose of this is to convey present knowledge regarding highway safety information for use by a broad array of transportation professionals"--p. xxiii, vol. 1.
Prediction Of The Expected Safety Performance Of Rural Two Lane Highways
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Author : Douglas W. Harwood
language : en
Publisher:
Release Date : 2000
Prediction Of The Expected Safety Performance Of Rural Two Lane Highways written by Douglas W. Harwood and has been published by this book supported file pdf, txt, epub, kindle and other format this book has been release on 2000 with Low-volume roads categories.
This report presents an algorithm for predicting the safety performance of a rural two-lane highway. The accident prediction algorithm consists of base models and accident modification factors for both roadway segments and at-grade intersections on rural two-lane highways. The base models provide an estimate of the safety performance of a roadway or intersection for a set of assumed nominal or base conditions. The accident modification factors adjust the base model predictions to account for the effects on safety for roadway segments of lane width, shoulder width, shoulder type, horizontal curves, grades, driveway density, two-way left-turn lanes, passing lanes, roadside design and the effects on safety for at-grade intersections of skew angle, traffic control, exclusive left- and right-turn lanes, sight distance, and driveways. The accident prediction algorithm is intended for application by highway agencies to estimate the safety performance of an existing or proposed roadway. The algorithm can be used to compare the anticipated safety performance of two or more geometric alternatives for a proposed highway improvement. The accident prediction algorithm includes a calibration procedure that can be used to adapt the predicted results to the safety conditions encountered by any particular highway agency on rural two-lane highways. The algorithm also includes an Empirical Bayes procedure that can be applied to utilize the safety predictions provided by the algorithm together with actual site-specific accident history data.
Evaluating Local And Tribal Rural Road Design With The Interactive Highway Safety Design Model Ihsdm
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Author : Xiao Qin
language : en
Publisher:
Release Date : 2013
Evaluating Local And Tribal Rural Road Design With The Interactive Highway Safety Design Model Ihsdm written by Xiao Qin and has been published by this book supported file pdf, txt, epub, kindle and other format this book has been release on 2013 with Electronic books categories.
Establishing performance-based safety goals and objectives becomes more attainable with the Highway Safety Manual (HSM). However, the safety performance functions (SPFs) in the HSM may not be accurate as they are not calibrated to local conditions. In addition, each SPF and crash modification factor (CMF) assumes a set of base site conditions which may not be realistic for local roadways. Although calibration procedures are available in HSM Part C Appendix A, they should be refined or modified to accommodate local data availability and roadway, traffic, and crash characteristics. It is also necessary to determine a set of base conditions applicable to local highways. This document presents the application of the HSM for rural local two-lane two-way highway segments in South Dakota (SD). The calibration was based on three-year (2009-2011) crash data from 657 roadway segments constituting more than 750 miles of roadways. The calibration process includes establishing new base conditions, developing SPFs, converting CMFs to base conditions as well as substituting default values with state-specific values. Five models have been developed and compared based on statistical goodness-of-fit and calibration factors. The same procedures were also conducted for the tribal two-lane two-way highway segments in SD based on three-year (2009-2011) crash data from 56 roadway segments constituting 199.5 miles of roadway. Results show that the jurisdiction-specific crash type distribution for CMFs can be drastically different from what is presented in the HSM. For rural local two-lane two-way roadways, the HSM method without modification underestimates SD crashes by 35 percent. The method based on SPFs developed from a full model has the best performance. For tribal two-lane two-way roadways, the HSM method without modification overestimates SD crashes by 122 percent. The method using the exponential from of annual average daily traffic (AADT) performs the best. This documentation provides important guidance and empirical results regarding how to calibrate HSM models.
Regional Considerations Of The Rocky Mountains And Plains Regions In Calibrating Safety Performance Function On Rural Two Lane Highwasy And Interstate Freeways
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Author : Rameshwor Chalise
language : en
Publisher:
Release Date : 2016
Regional Considerations Of The Rocky Mountains And Plains Regions In Calibrating Safety Performance Function On Rural Two Lane Highwasy And Interstate Freeways written by Rameshwor Chalise and has been published by this book supported file pdf, txt, epub, kindle and other format this book has been release on 2016 with Low-volume roads categories.
The American Association of State Highway and Transportation Officials, AASHTO’s Highway Safety Manual (HSM) was first released in 2010 and is considered as a significant milestone in the advancement of the practice of road safety analysis. An extensive workforce spearheaded by the Transportation Research Board (TRB) Committee gave a result in the form of the first Highway Safety Manual in the United States. The HSM has already been proven as a great asset in traffic safety practice and also in research related to traffic safety since it bridges the gap between the state-of-the-art of research and practice. The HSM’s analytical tools and techniques help to quantify the traffic safety and help in evaluation as well as decision making in planning design, operation, and maintenance. There are a number of states and transportation authorities which are already using the HSM along with the AASHTO design guide. Although the HSM is the sole national source for quantitative evaluation of traffic safety, it has some limitations and there remains some room for improvement. Safety Performance Functions are statistical models to predict the expected number of crashes per year for a certain roadway facility as a function of traffic, and, in some cases, roadway characteristics, and weather conditions. Simple SPFs are mostly developed using Average Annual Daily Traffic (AADT) only while Full SPFs consider additional factors to traffic such as roadway geometry, driver characteristics, and weather conditions. Part C-Predictive Methods in the HSM includes the calibration procedure of SPFs as well as guidelines on how to calibrate jurisdiction-specific SPFs. The main limitation in the HSM Part C is that the Safety Performance Functions (SPFs) for different road facilities were developed using data from only few states in the United States. Thus the provided SPFs cannot adequately represent all states and regions since each of the states has a different geographical features, weather conditions, crash reporting thresholds, and demographic attributes. The main goal of this research is to apply and validate some of the HSM parts; Part C, to Wyoming specific conditions. In this thesis, Wyoming-specific SPFs were developed using crash data and traffic data from 2003 to 2013 for both total crashes and fatal and injury (F+I) crashes. All the rural two-lane two-way roadways and interstate freeways were considered in developing Wyoming-specific Simple SPFs, however, segments were chosen randomly from different parts of the state to develop Wyoming-specific Full SPFs. Negative Binomial (NB) model was used to develop SPFs for both interstate freeways and two-lane two-way roadways. Also, Zero-Inflated Poisson (ZIP) model was developed for two-lane two-way roadways and compared with the NB model. Statistical goodness-of-fit tests were performed on the calibrated models. The results were compared in order to assess the transferability of the HSM SPFs in Wyoming. It was found that the HSM SPFs cannot be applied directly in the state of Wyoming. While Simple SPFs under-estimated and over-estimated the number of crashes for different roadway segments and severity levels, Wyoming-specific Full SPFs provided more accurate and precise crash prediction.
Estimating The Safety Effects Of Horizontal Curves On Pennsylvania Two Lane Rural Roads
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Author : Jeffrey Gooch
language : en
Publisher:
Release Date : 2015
Estimating The Safety Effects Of Horizontal Curves On Pennsylvania Two Lane Rural Roads written by Jeffrey Gooch and has been published by this book supported file pdf, txt, epub, kindle and other format this book has been release on 2015 with Rural roads categories.
Roadway departure crashes are three times more likely on horizontal curves than on tangent sections of two-lane rural highways. Research is needed to better quantify the safety performance (e.g., crash frequencies) of these crash-prone locations. Existing safety performance functions (SPFs) for two-way rural highways in the Highway Safety Manual (HSM) rely on base conditions that assume all roadway segments are tangent sections. The resulting predictions of crash frequency are then modified using a crash modification factor (CMF) that includes as independent variables the curve length, curve radius and presence of a spiral transition. Unfortunately, the CMF in the HSM does not have a standard error associated with it, which greatly limits its practical application and provides no indication of the level of uncertainty associated with the CMF. Other existing CMFs for horizontal curves in the FHWA CMF Clearinghouse also suffer from a lack of standard error and dated statistical methods, resulting in low to average star quality ratings (three or less). Furthermore, these existing CMFs treat individual curves as isolated geometric elements, even though recent research has shown that the safety performance of a horizontal curve is significantly influenced by its proximity to neighboring curves. Curves in close proximity to each other are expected to have lower crash frequency than those that are isolated because they are less likely to violate driver expectation. Failure to account for this distance may lead to erroneous predictions of crash frequency on horizontal curves.The objective of this study is to develop a high-quality CMF for horizontal curves on two-lane rural roads that takes into consideration the proximity of neighboring geometric elements using the most statistically rigorous modeling technique available, which reduces the potential for bias in the estimate of the CMF and provides a standard error that can be used to estimate the CMF uncertainty. This CMF is estimated using eight years of crash data (2005-2012) obtained from over 10,000 miles of state-owned two-lane rural roads in Pennsylvania. This comprehensive data includes information on roadway geometry (e.g., horizontal curvature, lane width, and shoulder width), traffic volume, access density, roadside hazard rating, and the presence of various low-cost safety countermeasures (e.g., centerline and shoulder rumble strips, curve and intersection warning pavement markings, and aggressive driving pavement dots). The propensity scores-potential outcomes method is applied, which matches each horizontal curve with tangent sections that are similar with respect to all other site characteristics (excluding crash frequency). The propensity scores are estimated using binary logistic regression, and curves and tangents are matched based on the propensity scores using the nearest neighbor matching technique with calipers and without replacement. Matching is performed across county lines to avoid individual horizontal curves being matched with its neighboring upstream or downstream tangent sections, which are likely to have very similar features and endogenous effects. Crash prediction is performed by means of random effects and mixed negative binomial regression using the explanatory variables mentioned above as well as distance to adjacent horizontal curves. The results indicate that degree of curvature, curve length, and traffic volume must be considered when predicting the frequency of total and fatal and injury crashes on horizontal curves. The presence of a horizontal curve and degree of curvature increase crash frequency, while the length of curve and traffic volumes decrease expected crash frequency. These results were consistent for both random and mixed effects models. The impact of the distance to adjacent curves was not found to be statistically significant. When predicting fixed object crashes, a proxy for roadway departure crashes, only degree of curvature and the presence of a horizontal curve were found to be statistically significant. All crash modification estimates for degree of curvature were consistent with the existing literature. The crash modification functions estimated are supplemented with formulas to estimate a conservative value for the standard error of the resulting CMF. The resulting crash modification functions in this thesis are recommended to evaluate safety at rural two-lane horizontal curves in Pennsylvania.
Identification Quantification And Structuring Of Two Lane Rural Highway Safety Problems And Solutions Volume Ii Physical And Safety Characteristics Of Two Lane Rural Highways Final Report
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Author : S. A. Smith
language : en
Publisher:
Release Date : 1983
Identification Quantification And Structuring Of Two Lane Rural Highway Safety Problems And Solutions Volume Ii Physical And Safety Characteristics Of Two Lane Rural Highways Final Report written by S. A. Smith and has been published by this book supported file pdf, txt, epub, kindle and other format this book has been release on 1983 with categories.