Safety Evaluation of Multiple Strategies at Stop-Controlled Intersections

Chapter 10. Summary and Conclusions

The objective of this study was to undertake a rigorous before–after evaluation of the safety effectiveness, as measured by crash frequency, of systemic low-cost improvements at stop-controlled intersections. The study used data from South Carolina to examine the effects for the specific crash types total, fatal and injury, rear-end, right-angle, and nighttime crashes. Based on the aggregate results, table 46 presents the recommended CMFs for the various crash types.

The disaggregate analysis sought to identify those conditions under which the multiple low-cost treatments are most effective. Variables of interest included area type (urban or rural), number of legs (three or four), lane configuration of the mainline and the cross street, traffic volumes, and expected crashes without treatment. The disaggregate analysis indicated larger crash reductions of all types for rural areas, four-legged intersections, and intersections with two-lane major roads. For total entering volume and expected crashes before treatment, the disaggregate analysis indicated the strategy is more effective on average for intersections with lower traffic volumes and fewer expected crashes per year. However, it is important to cautious in interpreting and applying the results of the other univariate comparisons, which are likely confounded my multiple correlative effects.

The B/C ratio, estimated with conservative costs and 3-year service life, considering the benefits for total crashes, is 12.4 to 1. With the USDOT recommended sensitivity analysis, these values could range from 7.1 to 1 up to 17.5 to 1. These results suggest that the multiple low-cost treatments, even with conservative assumptions on cost, service life, and the value of a statistical life, can be cost effective in reducing crashes at stop-controlled intersections.

This research demonstrates the potential effect of a systemic intersection improvement program by evaluating a systemic program where each site received an individualized version of a package of intersection treatments with some differences in application at each individual intersection. Although information regarding the exact treatments installed at each site was not available to the research team, such data would have value in future evaluations of multiple-strategy improvement projects. Agencies should consider how to best document and track the improvements at each site to facilitate more complete and rigorous disaggregate analyses. However, the approach used in this research is able to quantify the overall effects of an improvement program and suggests the expected effectiveness of similar future programs.