Developing local safety performance functions versus calculating calibration factors for SafetyAnalyst applications: a Florida case study

Safety performance functions (SPFs) are a required input to the newly released SafetyAnalyst software tool. Although SafetyAnalyst provides default SPFs that were developed based on data from multiple states in the United States, agencies have the option to calibrate local SPFs to better reflect their local conditions. However, the benefit from local calibration of SPFs is unclear and may vary from state to state. Using statistical goodness-of-fit measures and visual plots, this paper compares the performance of locally-calibrated SPFs using Florida data with the default SPFs from SafetyAnalyst for both freeway interchange influence areas and basic segments. An interchange influence area is one that extends 0.3 miles upstream and downstream of the respective gore point. Unlike for intersections, an automatic process for segmenting the influence areas for interchanges based on the above definition is relatively complex. Therefore, this paper also describes a spatial method to automatically segment a freeway facility into interchange influence areas and basic segments. Using four years of local crash data (2007-2010) from Florida, SPFs for both types of segments for both urban and rural areas were developed using the negative binomial regression model. The results showed that Florida-specific SPFs generally produced better-fitted models than the calibrated SafetyAnalyst default SPFs. This was clear in that the majority of Florida-specific models had higher Freeman-Tukey R-square (RFT2), as well as lower mean absolute deviance (MAD) and mean square prediction error (MSPE) estimates. Overall, the results suggest that agencies implementing SafetyAnalyst could improve their crash prediction by developing local-specific SPFs. 2014 Elsevier Ltd. Language: en

[1]  Darren J Torbic,et al.  SafetyAnalyst: Software Tools for Safety Management of Specific Highway Sites , 2007 .

[2]  Bhagwant Persaud,et al.  Assessing International Transferability of Highway Safety Manual Crash Prediction Algorithm and Its Components , 2012 .

[3]  J. Tukey,et al.  Transformations Related to the Angular and the Square Root , 1950 .

[4]  R Kulmala,et al.  Measuring the contribution of randomness, exposure, weather, and daylight to the variation in road accident counts. , 1995, Accident; analysis and prevention.

[5]  K. Sinha,et al.  Statistical Models for Prediction of Freeway Incidents , 2002 .

[6]  R. Shanmugam,et al.  Injury, Fatal, and Property Damage Accident Models for Highway Corridors , 1999 .

[7]  Li-Yen Chang,et al.  Analysis of freeway accident frequencies: Negative binomial regression versus artificial neural network , 2005 .

[8]  J F Kraus,et al.  Epidemiological aspects of fatal and severe injury urban freeway crashes. , 1993, Accident; analysis and prevention.

[9]  Kirolos Haleem,et al.  Clustering-Based Roadway Segment Division for the Identification of High-Crash Locations , 2013 .

[10]  Vasin Kiattikomol.  Freeway Crash Prediction Models for Long-Range Urban Transportation Planning , 2005 .

[11]  F Mannering,et al.  Effect of roadway geometrics and environmental factors on rural freeway accident frequencies. , 1995, Accident; analysis and prevention.

[12]  Meng Ma,et al.  Preparing Florida for deployment of SafetyAnalyst for all roads. , 2012 .

[13]  J. Lawless,et al.  Tests for Detecting Overdispersion in Poisson Regression Models , 1989 .

[14]  Bryan K Allery,et al.  Explicit Consideration of Safety in Transportation Planning and Project Scoping , 2004 .

[15]  Linjun Lu,et al.  Development of An Interface between FDOT's Crash Analysis Reporting System and the Safety Analyst , 2009 .

[16]  Bhagwant Persaud,et al.  ACCIDENT PREDICTION MODELS FOR FREEWAYS , 1993 .

[17]  Priyanka Alluri,et al.  Comparing Locally Calibrated and SafetyAnalyst-Default Safety Performance Functions for Florida’s Urban Freeways , 2012 .

[18]  Mitsuru Saito,et al.  Calibration of Highway Safety Manual Safety Performance Function , 2012 .

[19]  Fred L. Mannering,et al.  The statistical analysis of crash-frequency data: A review and assessment of methodological alternatives , 2010 .

[20]  Thomas Jonsson,et al.  Development of a Safety Performance Function for Motorcycle Accident Fatalities on Malaysian Primary Roads , 2013 .

[21]  Vasin Kiattikomol,et al.  Planning Level Regression Models for Prediction of Crashes on Interchange and Noninterchange Segments of Urban Freeways , 2008 .

[22]  Py Park,et al.  Comparing the Highway Safety Manual's Safety Performance Functions with Jurisdiction-Specific Functions for Intersections in Regina , 2012 .

[23]  Steven D Schrock,et al.  Developing a Regional Safety Performance Function for Rural Two-Lane Highways , 2012 .