Florida-based tables for intersection safety analysis developed
Florida’s requirements for reporting traffic crashes have changed in the last decade. The number of categories for crash reports has been reduced to include only those crashes involving hit-and-run, fatality, DUI, and injury, thus reducing by about 60 percent the quantity of accident data available. This lack of data has resulted in difficulty in the identification, justification, and priority ranking of intersection safety improvements. If the anticipated consequences of hazardous conditions are to be resolved, there is a need to supplement the available crash data (or sometimes to use surrogate data, such as vehicle conflict data and their relationship to actual crashes) to identify and analyze intersection safety problems.
CUTR recently completed a comprehensive traffic conflict study under contract with the FDOT State Safety Office to observe traffic conflicts, collect crash data, and develop user-friendly tables for predicting crashes at intersections. Objectives were to:
- investigate the validity of current national conflict tables;
- develop similar tables that apply to intersections and crash rates in Florida; and
- implement the study by using the conflict tables in Department safety improvement projects.
For the study, the 15 most common intersection types were identified and categorized based on signalization, number of legs, and through-laneage of the intersections. Thirteen traffic conflict types were surveyed from 178 intersections randomly sampled from a five-county area in west central Florida (Hillsborough, Manatee, Pasco, Polk, and Sarasota).
The most recent three-year (1992-1994) crash history of the sampled intersections was collected from local governments and compared to the conflict counts. Based on the conflict and crash data, new and easy-to-use tables were developed.
Results of this study can be used to develop criteria in the development, justification, and prioritization of intersection safety improvement projects in accordance with FDOT’s “Highway Safety Improvement Program Guideline.” The new tables provide mean, 90th, and 95th percentile conflict rates for each intersection type and conflict type to evaluate the relative safety and operations problems at intersections, and crash-to-conflict ratios have been developed to be used in formulas to estimate intersection crashes by type.
A final report, a training guide, and a set of tables were the result of this research. The tables can be used to:
- identify intersections with safety and operations problems;
- identify high risk vehicle movements (the most frequently-occurring conflict types) at intersections and take remedial action;
- prioritize safety improvements for a selected number of intersections;
- estimate expected crashes at newly-built or recently-changed intersections;
- estimate crashes at intersections where recent historical crash reports are not readily accessible or do not exist; and
- study intersections other than high crash intersections.
For further information, contact CUTR Senior Research Associate and ITS Program Manager Mike Pietrzyk at pietrzyk@cutr.usf.edu, (813) 974-3120.
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