Evaluation of Safety Performance Functions Based on Experimental Design Using a Cross-Validation Method

2017 ◽  
Vol 2636 (1) ◽  
pp. 62-72 ◽  
Author(s):  
Jung-Han Wang ◽  
Mohamed A. Abdel-Aty ◽  
Jaeyoung Lee
Keyword(s):  
Goodness Of Fit ◽  
Cross Validation ◽  
Safety Performance ◽  
Major Road ◽  
Highway Safety Manual ◽  
Annual Average Daily Traffic ◽  
Minor Road ◽  
Safety Performance Functions ◽  
The One ◽  
Leave One Out

The Highway Safety Manual (HSM) Part C provides a series of safety performance functions (SPFs) for different roadway conditions. The SPFs suggested in the HSM are formulated on the basis of exposure variables: the logarithms of the annual average daily traffic (AADT) on the major road and on the minor road under the base condition. In this research, data from 7,802 intersections in Florida were collected and processed. These intersections were categorized into seven types based on area type (rural or urban), number of legs (three or four), and number of approaches controlled by stop signs. Twenty-two SPF formulations, including the one suggested by the HSM, were developed for each intersection type for examination of the goodness-of-fit measures of the SPFs. In addition, the goodness of fit of each model of the 22 SPFs in each category was examined with 10-fold leave-one-out cross-validation (LOOCV). With a comparison of the delta values generated with the LOOCV method, it is suggested that the SPF with the logarithm of the total entering vehicle volume and the ratio of the AADT on the minor road and the AADT on the major road are important. In addition, the SPFs with the AADT on the major road and the AADT on the minor road and their logarithmic transformations are also important. Therefore, it is suggested that the future HSM compare these two SPF formulations—as suggested in the current research, along with the original SPF formulation in the manual—and select the one with the best model fit on the basis of the delta value using LOOCV.

scholarly journals Calibration of the Highway Safety Manual and the SafetyAnalyst Methodologies for Ontario Highways

2021 ◽  
Author(s):  
Ali Sabbaghi
Keyword(s):  
Road Safety ◽  
Goodness Of Fit ◽  
Highway Safety ◽  
Safety Performance ◽  
Data Set ◽  
Rural Highways ◽  
Part C ◽  
Highway Safety Manual ◽  
Safety Performance Functions ◽  
Central Regions

SafetyAnalyst and the Highway Safety Manual (HSM) are two tools that are expected to revolutionize highway safety analyses. A key issue that allows SafetyAnalyst and HSM to become the new standards in road safety engineering is the calibration of their safety performance functions (SPFs) across time and jurisdictions. In this study, the methodologies of SafetyAnalyst and HSM are calibrated for Ontario to evaluate the effective transferability of their SPFs to local topographical conditions. A SafetyAnalyst calibration has been completed for Ontario highways and freeways, intersections, and ramps for six years (1998-2003) of traffic and accident counts. A data set which consists of 78 kilometres of rural two-lane two-way highways and 71 three- and four-legged stop controlled intersections located in the eastern and central regions of the Ministry of Transportation of Ontario (MTO) with six years (2002 to 2007) of traffic volume and collision counts has been used to evaluate the HSM SPFs to Ontario data. Several goodness-of-fit (GOF) measures are computed to assess the transferability and suitability of the crash models for applicability in Ontario. The study suggests that while most of the SafetyAnalyst SPFs for highways and ramps are not adaptable to Ontario data, the recalibrated SafetyAnalyst SPFs for intersections and also the recalibrated HSM Part C predictive models for two-lane rural highways and intersections provide satisfactory results in comparison to the crash models developed specifically for Ontario. Finally, this research highlights the substantial need for future improvements in data quality for more reliable safety performance estimations and evaluations.

scholarly journals Calibration of the Highway Safety Manual and the SafetyAnalyst Methodologies for Ontario Highways

2021 ◽  
Author(s):  
Ali Sabbaghi
Keyword(s):  
Road Safety ◽  
Goodness Of Fit ◽  
Highway Safety ◽  
Safety Performance ◽  
Data Set ◽  
Rural Highways ◽  
Part C ◽  
Highway Safety Manual ◽  
Safety Performance Functions ◽  
Central Regions

SafetyAnalyst and the Highway Safety Manual (HSM) are two tools that are expected to revolutionize highway safety analyses. A key issue that allows SafetyAnalyst and HSM to become the new standards in road safety engineering is the calibration of their safety performance functions (SPFs) across time and jurisdictions. In this study, the methodologies of SafetyAnalyst and HSM are calibrated for Ontario to evaluate the effective transferability of their SPFs to local topographical conditions. A SafetyAnalyst calibration has been completed for Ontario highways and freeways, intersections, and ramps for six years (1998-2003) of traffic and accident counts. A data set which consists of 78 kilometres of rural two-lane two-way highways and 71 three- and four-legged stop controlled intersections located in the eastern and central regions of the Ministry of Transportation of Ontario (MTO) with six years (2002 to 2007) of traffic volume and collision counts has been used to evaluate the HSM SPFs to Ontario data. Several goodness-of-fit (GOF) measures are computed to assess the transferability and suitability of the crash models for applicability in Ontario. The study suggests that while most of the SafetyAnalyst SPFs for highways and ramps are not adaptable to Ontario data, the recalibrated SafetyAnalyst SPFs for intersections and also the recalibrated HSM Part C predictive models for two-lane rural highways and intersections provide satisfactory results in comparison to the crash models developed specifically for Ontario. Finally, this research highlights the substantial need for future improvements in data quality for more reliable safety performance estimations and evaluations.

Simple Index to Assess the Calibration Quality of Safety Performance Functions Based on Multiple Goodness-of-Fit Metrics

2021 ◽  
pp. 036119812110088
Author(s):  
Raul E. Avelar ◽  
Karen Dixon ◽  
Boniphace Kutela ◽  
Sam Klump ◽  
Beth Wemple ◽  
...  
Keyword(s):  
Goodness Of Fit ◽  
Synthetic Data ◽  
Calibration Procedure ◽  
Safety Performance ◽  
Absolute Deviation ◽  
Data Set ◽  
Safety Database ◽  
Simple Index ◽  
Safety Performance Functions

The calibration of safety performance functions (SPFs) is a mechanism included in the Highway Safety Manual (HSM) to adjust SPFs in the HSM for use in intended jurisdictions. Critically, the quality of the calibration procedure must be assessed before using the calibrated SPFs. Multiple resources to aid practitioners in calibrating SPFs have been developed in the years following the publication of the HSM 1st edition. Similarly, the literature suggests multiple ways to assess the goodness-of-fit (GOF) of a calibrated SPF to a data set from a given jurisdiction. This paper uses the calibration results of multiple intersection SPFs to a large Mississippi safety database to examine the relations between multiple GOF metrics. The goal is to develop a sensible single index that leverages the joint information from multiple GOF metrics to assess overall quality of calibration. A factor analysis applied to the calibration results revealed three underlying factors explaining 76% of the variability in the data. From these results, the authors developed an index and performed a sensitivity analysis. The key metrics were found to be, in descending order: the deviation of the cumulative residual (CURE) plot from the 95% confidence area, the mean absolute deviation, the modified R-squared, and the value of the calibration factor. This paper also presents comparisons between the index and alternative scoring strategies, as well as an effort to verify the results using synthetic data. The developed index is recommended to comprehensively assess the quality of the calibrated intersection SPFs.

scholarly journals Crash Prediction Models for Horizontal Curve Segments on Two-Lane Rural Roads in Thailand

2021 ◽  
Vol 13 (16) ◽  
pp. 9011
Author(s):  
Nopadon Kronprasert ◽  
Katesirint Boontan ◽  
Patipat Kanha
Keyword(s):  
Prediction Models ◽  
Safety Performance ◽  
Horizontal Curve ◽  
Crash Frequency ◽  
Rural Roads ◽  
Crash Prediction ◽  
Road Crashes ◽  
Highway Safety Manual ◽  
Safety Performance Functions ◽  
Crash Prediction Models

The number of road crashes continues to rise significantly in Thailand. Curve segments on two-lane rural roads are among the most hazardous locations which lead to road crashes and tremendous economic losses; therefore, a detailed examination of its risk is required. This study aims to develop crash prediction models using Safety Performance Functions (SPFs) as a tool to identify the relationship among road alignment, road geometric and traffic conditions, and crash frequency for two-lane rural horizontal curve segments. Relevant data associated with 86,599 curve segments on two-lane rural road networks in Thailand were collected including road alignment data from a GPS vehicle tracking technology, road attribute data from rural road asset databases, and historical crash data from crash reports. Safety Performance Functions (SPFs) for horizontal curve segments were developed, using Poisson regression, negative binomial regression, and calibrated Highway Safety Manual models. The results showed that the most significant parameter affecting crash frequency is lane width, followed by curve length, traffic volume, curve radius, and types of curves (i.e., circular curves, compound curves, reverse curves, and broken-back curves). Comparing among crash prediction models developed, the calibrated Highway Safety Manual SPF outperforms the others in prediction accuracy.

Calibration of the Highway Safety ManualGiven Safety Performance Functions for RuralMultilane Segments and Intersections in Kansas

2017 ◽  
Author(s):  
Syeda Rubaiyat Aziz ◽  
Sunanda Dissanayake
Keyword(s):  
Safety Evaluation ◽  
Highway Safety ◽  
Safety Performance ◽  
Regression Coefficients ◽  
Local Conditions ◽  
Crash Prediction ◽  
Highway Safety Manual ◽  
Satisfactory Level ◽  
Safety Performance Functions ◽  
Predictive Methods

The Highway Safety Manual (HSM) provides models and methodologies for safety evaluation and prediction of safety performance of various types of roadways. However, predictive methods in the HSM are of limited use if they are not calibrated for local conditions. In this study, calibration procedures given in the HSM were followed for rural segments and intersections in Kansas. Results indicated that HSM overpredicts fatal and injury crashes and underpredicts total crashes on rural multilane roadway segments in Kansas. Therefore, existing safety performance functions (SPFs) must be adjusted for Kansas conditions, in order to increase accuracy of crash prediction. This study examined a way to adjust HSM calibration procedures by development of new regression coefficients for existing HSM-given SPF. Final calibration factors obtained through modified SPFs indicated significant improvement in crash prediction for rural multilane segments in Kansas. Additionally, obtained calibration factors indicated that the HSM is capable of predicting crashes at intersections at satisfactory level.

Highway Safety Manual Calibration: Assessing Alternate Definitions of the Calibration Factor

2018 ◽  
Vol 2672 (30) ◽  
pp. 99-108 ◽  
Author(s):  
Mahdi Rajabi ◽  
Jennifer Harper Ogle ◽  
Patrick Gerard
Keyword(s):  
Goodness Of Fit ◽  
Prediction Models ◽  
Highway Safety ◽  
Calibration Factor ◽  
Crash Frequency ◽  
Calibration Process ◽  
Highway Safety Manual ◽  
Safety Performance Functions ◽  
Safety Studies ◽  
Using Data

The publication of the Highway Safety Manual (HSM) in 2010 established crash frequency prediction as the essential safety measure for safety studies. However, given that the models were developed using a single state’s data, the HSM recommends calibration of the prediction models using data from the jurisdiction where they will be applied. This calibration process has been conducted in several states and many questions have been raised as a result. This paper is intended to investigate different definitions and criteria for the calibration factors, and provide recommendations for practitioners on which definition to use. In addition to the calibration factors in the HSM and previously published definitions, two other calibration factor equations are proposed and compared using multiple goodness of fit measures. Whereas each definition may outperform others in certain measures, in this study, it is recommended to use the definition that maximizes the likelihood between predicted and observed crashes. The idea is to follow the same concept in both state-specific safety performance functions development and calibration process, which is maximizing the likelihood of predicted and observed crashes.

Jurisdiction-Specific versus SafetyAnalyst-Default Safety Performance Functions: Case Study on Two-Lane and Multi-Lane Arterials

2019 ◽  
Vol 2673 (10) ◽  
pp. 501-509
Author(s):  
Hector Vargas ◽  
Asif Raihan ◽  
Priyanka Alluri ◽  
Albert Gan
Keyword(s):  
Empirical Bayes ◽  
Goodness Of Fit ◽  
Safety Management ◽  
Safety Performance ◽  
Regression To The Mean ◽  
Absolute Deviation ◽  
Local Conditions ◽  
Screening Criteria ◽  
Rural And Urban ◽  
Safety Performance Functions

Network screening is the most important step in the highway safety management process. Screening criteria based on the empirical Bayes (EB) approach are considered to be most reliable as it accounts for the regression-to-the-mean bias. However, the EB approach requires safety performance functions (SPFs), preferably calibrated to local conditions, which are often unavailable. The SafetyAnalyst software, developed by the Federal Highway Administration, automates the EB approach using the default SPFs which were developed using multiple states’ data. Local agencies are encouraged to develop jurisdiction-specific SPFs to better reflect local conditions. However, the benefits of developing local SPFs for rural and urban two-lane and multi-lane highway facilities are unclear and may vary from state to state. This research compares the performance of Florida-specific SPFs with SafetyAnalyst-default SPFs calibrated to Florida data using mean absolute deviation, mean squared predicted error, and Freeman-Tukey R-square goodness-of-fit measures. The results showed that Florida-specific SPFs generally produced better-fitted models than the calibrated SafetyAnalyst-default SPFs. In contrast, when the crash prediction capabilities of the already-available local SPFs, calibrated to the latest time period for which they will be applied, are compared with the calibrated SafetyAnalyst-default SPFs, the calibrated SafetyAnalyst-default SPFs in general were found to better predict crash frequencies compared with the existing Florida-specific SPFs calibrated to the latest data. Therefore, the local SPFs are recommended when developed using present data; however, the calibrated SafetyAnalyst-default SPFs could be used if local SPFs developed from present data are not available.

scholarly journals Safety performance functions in Dedicated Bus Lane of BRT on Caracas Avenue Corridor at Bogotá city

Inge CUC ◽  
2019 ◽  
Vol 15 (2) ◽  
pp. 66-77
Author(s):  
Kelly Andrea Rodríguez Polo ◽  
Santiago Henao Pérez
Keyword(s):  
Traffic Accidents ◽  
Negative Binomial ◽  
Central Line ◽  
Safety Performance ◽  
Transport Systems ◽  
Accident Prediction ◽  
Highway Safety Manual ◽  
Safety Performance Functions ◽  
Traffic Volumes ◽  
Bus Lane

Introduction- Road safety is a global concern due to the fact that traffic accidents represent serious temporary and / or permanent damage to the health of those involved. On the other hand, the Bus Rapid Transit (BRT) systems carries a large volume of passengers and during their operation; they are involved in this problem. Objective- Accident prediction model implemented in the Highway Safety Manual 2010 or HSM is an alternative to evaluate the strategies that allow to reduce accidents in this type of systems. However, there is not specified safety performance functions (SPFs) developed for BRT systems. In the present work, the accident model of HSM is adapted by calibration of general SPFs expressions of the manual and also, SPFs were developed for BRTs installed on the central-line of main roads and use an exclusive lane of all other transport systems (both public or private) and mobility (e.g. bike paths). Method / Results - Crashes reports and traffic volumes data supplied by the Department of Transportation of Bogotá were used. The model was calibrated using the safety performance functions (SPFs) of the HSM and a specific developed functions for the BRT conditions. These SPFs were developed using a negative binomial model in roadway segments and intersections. Conclusions- Through the validation, it was found that the functions developed have a better fit than the established SPF of the HSM. The developed SPFs can be used as a tool to define safety performance guidelines of Bogotá's BRT corridors in the coming years.

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