Safety Evaluation of Edge-Line Rumble Stripes on Rural Two-Lane Horizontal Curves

Chapter 9. Summary and Conclusions

The objective of this study was to perform a rigorous before–after evaluation of the safety effectiveness, as measured by crash frequency, of ELRSs applied on rural two-lane horizontal curves. The study used data from Kentucky and Ohio to examine the effects for specific crash types, including total, fatal and injury, ROR, nighttime, and nighttime ROR crashes. Crashes occurring at or related to intersections, as well as animal-related crashes, were not included. Based on the aggregate results, table 26 and table 27 show the recommended CMFs for the various crash types. Note that the results for Kentucky were based on smaller sample sizes and that the results for Ohio included the effects of a statewide horizontal curve warning sign upgrade program.

*Statistically significant results at the 95-percent confidence.

*Statistically significant results at the 95-percent confidence.

To date, the most comprehensive and reliable study of SRSs was published by Torbic et al.⁽¹⁰⁾Compared with the results of that study for ELRSs, the results of the current study suggest that greater reductions in all crash types may be found by placing rumble strips on or near the edge line for horizontal curves.

A disaggregate analysis of the results of the current study indicated that larger safety benefits were found for horizontal curves with AADT greater than 4,000 for all crash types; however, the differences by AADT were not statistically significant at the 95-percent confidence level. The disaggregate analysis further indicated larger safety benefits for horizontal curves with a higher before-period expected crash frequency. The results suggested no benefit for curves with low before-period expected crash frequencies for all crash types. The difference in CMFs that were dependent on before-period expected crash frequency were statistically significant for total and ROR crashes. Caution should be used in interpreting and applying these disaggregate results; however, the disaggregate analysis CMFs may be used in prioritizing treatment sites.

Estimated B/C ratios range from 189:1 to 467:1 for Kentucky and from 272:1 to 672:1 for Ohio. On first inspection, the B/C ratios were larger than would reasonably be expected for an installation of this type. However, the installations took place on corridors, while the analysis only looked at the safety effects on horizontal curves. Horizontal curves have higher crash rates than overall corridors, and the cost per mile of installation would not be representative for installations only on horizontal curves. For a curve-specific treatment, the B/C ratio would likely be reduced owing to the higher deployment cost for spot-specific installations. Regardless, these results suggest that the treatment, even in its most expensive variation, can be highly cost effective.