Horizontal curves represent a considerable safety problem on rural two-lane highways. Curves experience a higher accident rate than tangents. Current road improvements highlight the issue of what else should be done at horizontal curves to enhance (or at least hold constant) the level of safety at these sites. There has been a need to better quantify accident effects of curve features and to quantify the effects on accidents of curve flattening, curve widening, addition of spiral transitions, improvement to deficient superelevation, and improvements to the roadside. The purpose of this research was to determine the horizontal curve features which affect accident experience on two lane rural roads and, also, to determine which types of geometric improvements on curves will affect accident experience and to what extent.

CD-ROM contains full report, plus RSRAP (Resurfacing Safety Resource Allocation Program) software and supplemental material.