Effects of geometry and pavement friction on horizontal curve crash frequency

ABSTRACT

Horizontal curves tend to be associated with a disproportionate number of severe crashes. Many treatments have been proposed to reduce traffic crashes and fatalities occurring on horizontal curves. The application of high-friction surface treatments is one among many treatments that agencies have been considering. However, relatively less research has been conducted on the safety implications of pavement friction improvements caused by these treatments. Before–after case studies have been conducted on the effectiveness of high-friction surface treatments, but pavement variables like skid number (coefficient of friction multiplied by 100) have not yet been incorporated into safety prediction methodologies. The objective of this study is to develop a crash modification factor (CMF) for skid number for all crashes, wet-weather crashes, run-off-the-road crashes, and wet-weather run-off-the-road crashes. A horizontal curve database from a southern state in the United States was used to accomplish the study objective. The skid number variable was found to be statistically significant, in addition to traditional variables such as traffic volume, curve radius, and cross-sectional widths. The CMF developed in this study can be applied to evaluate the safety performance of a curve of interest and estimate the potential safety benefit of installing a high-friction surface treatment.

KEYWORDS:

• horizontal curves
• friction
• skid number
• safety performance function
• crash modification factors

Acknowledgment

The author would like to thank Mr. Darren McDaniel, PE, Safety Engineer, at Texas Department of Transportation for his input. His comments were greatly appreciated.