Road Safety Prediction

Section A. Guidelines for Using Crash Prediction Models

Implementation Products

NCHRP Project 17-93: Updating Safety Performance Functions for Data-Driven Safety Analysis. This project developed guidelines for calibrating or updating a crash prediction model (CPM). The guidelines are applicable to the CPMs in Part C of the Highway Safety Manual (HSM) and similar CPMs developed for a specific jurisdiction. These guidelines are intended to provide a balance between the effort required to implement the calibration process and the predictive reliability of the calibrated CPM.

Guidelines for Best Use of HSM Predictive Models for Alternatives Analysis.  Presentation for TRB Annual Meeting, Session 1027, January 2021. This presentation describes guidelines for developing a reliable estimate of the change in safety associated with the implementation of an alternative design. The guidelines are based on information provided in Part C of the HSM.  SLIDES    SPEAKER NOTES

TxDOT Report 0-4703-P5: Procedure for Using Accident Modification Factors in the Highway Design Process. J. Bonneson and K. Zimmerman. This document describes a procedure for using accident modification factors (AMFs) in the highway design process. Application of the procedure entails the use of several AMFs, where each AMF addresses one specific design element (such as lane width, shoulder width, curve radius, etc.). The procedure can be used to evaluate the safety benefits associated with alternative geometric designs. REPORT

Research Reports

NCHRP Project 17-93: Updating Safety Performance Functions for Data-Driven Safety Analysis. This project developed guidelines for calibrating or updating a crash prediction model (CPM) like those in Part C of the HSM. These guidelines are intended to provide a balance between the effort required to implement the calibration process and the predictive reliability of the calibrated CPM.

TxDOT Report 0-4703-5: Calibration Factors Handbook:  Safety Prediction Models Calibrated with Texas Highway System Data.  J. Bonneson and M. Pratt.  This document summarizes the research conducted and the conclusions reached during the development of safety prediction models for intersections and highway segments in Texas. Models were developed for urban and suburban arterial intersections, urban and suburban arterial street segments, rural multilane highway segments, and urban and rural freeway segments.  REPORT

TxDOT Report 0-4703-4:  Development of Tools for Evaluating the Safety Implications of Highway Design Decisions. J. Bonneson, D. Lord, K. Zimmerman, K. Fitzpatrick, and M. Pratt. This document summarizes the research conducted and the findings for the initial three years of the project. This research included a review of the TxDOT design and safety evaluation process, identification of the safety information sources and needs, identification of the data needed to use selected crash prediction models, assessment of the applicability of accident modification factors for design evaluation, and calibration of selected crash prediction models for Texas application.  REPORT


Section B. Predictive Models for Evaluating Specific Facility Types

Implementation Products

Generalized Safe System Analysis Tool (GSSAT). This tool provides the analyst with information about how well a particular intersection design aligns with safe system principles. It was developed to embrace the flexibility of the safe system analysis methodology described in FHWA Report FHWA-SA-21-008. The current version of the tool is intended to support the scoping phase of the project development process, where alternative intersection configurations and control modes are being considered.  GSSAT can be used to evaluate any intersection form. It requires the analyst to identify each conflict point at the intersection of interest. Then, for each of these points, the analyst must identify the conflicting movements and control mode (e.g., signalized, yield, stop).   SPREADSHEET

Note: A 2022 security change by Microsoft prevents Excel files with macros (i.e., with the .xlsm extension) from running unless the analyst changes the file properties to unblock the file macros. Right-click on the filename, select Properties, select General, in the Security section (at the bottom) check the "Unblock" checkbox, and select OK.

TxDOT Report 0-4703-P2:  Roadway Safety Design Workbook. J. Bonneson and M. Pratt. This document provides the best-available information describing the relationship between various highway geometric design components and crash frequency. This document focuses on quantitative safety relationships for specific design components known to be correlated with crash frequency. It is intended for engineers responsible for the geometric design of streets and highways. REPORT   SPREADSHEET

NDOR Project RES1(0099) P471: Guidelines for Realignment of Skewed Intersections. P. McCoy, E. Tripi, and J. Bonneson.  This report describes guidelines for the realignment of unsignalized, skewed intersections on rural two-lane highways. The guidelines are based on a cost-benefit analysis of skewed intersection realignment. Benefits include delay and crash reduction.   REPORT

Research Reports

FDOT Project CA694-TWO8: Roadway Segment and Unsignalized Intersection SPF Development and Network Screening Process. This report documents the development of SPFs, CMFs, and benefit-cost evaluation procedures for road safety management. The SPFs and CMFs are focused on road segment evaluation (including any unsignalized access points along the segment).  REPORT

FDOT Project CA58-TWO13: Florida Part C SPF/CMF Development - Phase 2: This project developed two reports that collectively document the development of crash prediction models (CPMs) that include SPFs and CMFs for signalized intersections having selected context classifications. Class C3R - suburban residential, C3C - suburban commercial, C4 - urban general.

FDOT Project CAS11-TWO6: Florida Part C SPF/CMF Development - Phase 3: This project developed two reports that collectively document the development of crash prediction models (CPMs) that include SPFs and CMFs for signalized intersections having selected context classifications. Class C1 - natural, C2 - rural, C2T - rural town, C5 - urban center, C6 - urban core.

NCHRP Project 03-120: Assessing Interactions Between Access Management Treatments and Multimodal Users.This project developed two working papers that summarize the development of a CPM for predicting truck-related crash frequency and a CPM for predicting transit-related crash frequency. The two CPMs are described in the papers listed below. They are also documented in the project Final Report (NCHRP  Web-Only document 256). 


Section C. Roadside Safety Prediction

Implementation Products

NCHRP Project 17-72: Update of Crash Modification Factors for the Highway Safety Manual. This project developed a procedure for computing a roadside design CMF for two-lane rural highways. The CMF is intended to replace the Roadside Design CMF that is described in Chapter 10 of the HSM. The procedure is also documented in Appendix O of the project Final Report (NCHRP Web-Only document 352). 

Research Reports

NCHRP Project 17-104: Enhancement of Roadside Design Safety Prediction Models for the Highway Safety Manual. This project reviewed the literature related to information describing the safety effect of roadside design features. The following two working papers summarize the findings from the literature review.

NCHRP Project 17-72: Update of Crash Modification Factors for the Highway Safety Manual. This project developed a procedure for computing a roadside design CMF for two-lane rural highways. The CMF is intended to replace the Roadside Design CMF that is described in Chapter 10 of the HSM. The process used to develop the procedure is described in the paper listed below. It is also documented in Appendix N of the project Final Report (NCHRP Web-Only document 352).  


Section D. Related Topics

Implementation Products

TxDOT Product 5-4703-01-P6: Training Course Slides. As part of TxDOT Project 0-4703, a series of workshops were developed to share safety information with TxDOT roadway designers. Information in the Workbook was used as the basis for the workshops. The workshops addressed rural highways, urban streets, and freeways. They included a mixture of classroom discussion and hands-on training activities for the participants. SLIDES 

TxDOT Report 0-4703-P1:  Roadway Safety Design Synthesis. J. Bonneson, K. Zimmerman, and K. Fitzpatrick. This document describes the effect of key design components on street and highway safety. The information presented represents the findings from a critical review of the literature and an evaluation of the reported safety trends and relationships. REPORT  

Research Reports

TxDOT Report 0-4703-7: Development of Safety Performance Monitoring Procedures. M. Pratt and J. Bonneson. This report summarizes the research that was conducted and the products that were developed during a six-year project. A key objective of the project was to develop quantitative road safety evaluation guidelines and tools. The report also describes a plan to incorporate the guidelines and tools into the project development process.   REPORT