Freeway Safety Prediction
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Implementation Products
NCHRP Project 17-45: Enhanced Interchange Safety Analysis Tool (ISATe). J. Bonneson, M. Pratt, S. Geedipally, D. Lord, T. Neuman, and J. Moller. ISATe provides information about the relationship between freeway design features and safety. It is based on research that quantified the relationship between various design elements and expected average crash frequency. The information provided by ISATe is intended to help designers make informed judgments about the safety performance of design alternatives. SPREADSHEET USER MANUAL
NCHRP Project 17-45: Freeway and Interchange Safety Evaluation Workshop. This workshop informs participants about new methods for evaluating freeway and interchange safety. It is based on the safety prediction methods developed for Project 17-45, described in the Final Report, and automated in ISATe. The workshop consists of about seven hours of instruction. AGENDA INSTRUCTOR GUIDE SLIDES
Research Reports
NCHRP Project 17-45: Safety Prediction Methodology and Analysis Tool for Freeways and Interchanges - Final Report. J. Bonneson, S. Geedipally, M. Pratt, and D. Lord. This report documents the development of a safety prediction method for freeways that is suitable for incorporation in the Highway Safety Manual (HSM). The method addresses freeway segments, freeway speed-change lanes, ramp segments, collector-distributor roads, and crossroad ramp terminals. REPORT
Report appendices:
Appendix A - Practitioner Interviews
Appendix B - Database Enhancement
Appendix C - Proposed HSM Freeways Chapter [download Appendix C]
Appendix D - Proposed HSM Ramps Chapter [download Appendix D]
Appendix E - Proposed HSM Appendix B for Part C [download Appendix E]
Appendix F - Algorithm Description
Errata for Appendices C, D, and E (June 18, 2014) [download errata]
NCHRP Project 17-89: Safety Performance of Part-Time Shoulder Use on Freeways. The objectives of this research were to (1) develop quantitative tools for practitioners to use to evaluate safety performance of freeways with part-time shoulder use (PTSU) as a function of temporal, operational, and other conditions when the shoulder is open or closed to traffic, and (2) use the tools to determine the safety performance of part-time shoulder use, in order to better inform state DOT decision making on their application.
Working Paper 9a - Crash Prediction Model for Freeways with Part-Time Shoulder Use. This paper describes the findings obtained during the development of crash prediction models (CPMs) for freeways with PTSU operation. The models are used to predict the average crash frequency associated with one direction of travel on a freeway. Each CPM includes a safety performance function (SPF), one or more adjustment factors (AFs), a calibration factor, a severity distribution, and a crash type distribution.
Working Paper 9b - Crash Type and Severity Distributions for Freeways with Part-Time Shoulder Use. This paper describes the findings obtained during the development of crash severity and crash type distributions for freeways with PTSU operation. A predictive model was developed for computing the crash severity distribution. A table of proportions was developed for computing the crash type distribution.