Study of Accidents at Signalized Intersections -- Phase I Final Report

Wolverton, Jereen J.; Mounce, John M. · 1997 · ROSA P / Montana. Department of Transportation. Research, Development and Technology Transfer Program

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Summary

This Phase I report, conducted by Montana State University for the Montana Department of Transportation, examines accident patterns and trends at signalized intersections in Montana to identify causal factors susceptible to correction. The study was motivated by increasing traffic demand and public requests for signal installations, alongside a need to reconcile public perception with engineering realities regarding safety benefits. The research objectives included conducting a literature review, assimilating accident trend statistics, establishing variables of influence, and determining significant causal patterns. The methodology involved a comprehensive literature review of existing studies on signal safety effects, clearance intervals, and enforcement technologies. For the empirical component, the researchers analyzed accident data from 1992 to 1994 across Montana. They evaluated variables including accident type, severity, alcohol involvement, roadway conditions, driver age, and contributing factors. Accident trends were compared across Montana’s six largest cities: Billings, Great Falls, Missoula, Butte, Helena, and Bozeman. Additionally, accident rates were calculated along State Primary Routes, and twenty-five specific intersections were selected for detailed analysis using accident report files and constructed collision diagrams. The findings indicate that Montana’s accident characteristics are similar to those reported in other states and studies. Angle and rear-end accidents accounted for the largest percentages of accident types at signalized intersections. The analysis revealed that traffic volume and the population of the city where accidents occurred were significant variables affecting accident rates. Accident type percentages were consistent across the six major cities studied. The literature review highlighted that while signalization typically reduces right-angle accidents, it can increase rear-end collisions. Furthermore, the review noted that inadequate clearance interval timing is statistically associated with higher crash rates, and that automatic enforcement of red-light violations can significantly reduce violations when accompanied by public awareness. The significance of this study lies in its establishment of baseline accident patterns for Montana, confirming that local trends align with national data. By identifying traffic volume and population as key influencers, the report provides a foundation for future safety improvements. The findings support the need for proper signal timing and coordination to mitigate specific accident types, particularly rear-end and angle collisions. This Phase I report serves as a precursor to further investigation into corrective measures for signalized intersection safety in the state.

Key finding

Angle and rear-end accidents accounted for the largest percentages of accident types, with traffic volume and city population identified as the primary variables affecting accidents.

Methodology

dataset

Sample size: 25

Provenance

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Summary generated by qwen3.6-27b-prismaquant on 2026-06-10; verification: verified.

Topics

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• roadway lighting effects
• incidence prevalence
• intersection design

Information type

What kind of knowledge this paper contributes, grouped by family — independent of topic (what it is about) and method (how it was studied).

• Empirical Findings: crash risk outcomes