The purpose of this study was to determine the horizontal curve features which affect safety and traffic operations and to quantify the effects on accidents of various curve-related improvements. The primary data base developed and analyzed consisted of 10,900 horizontal curves in Washington State. Three existing Federal data bases on curves were also analyzed. These data bases included the cross-section data base of nearly 5,000 mi (8,050 km) of roadway from 7 States, a surrogate data base of vehicle operations on 78 curves in New York State, and 3,277 curve segments from 4 States. Based on statistical analyses and model development, variables found to have a significant effect on accidents include degree of curve, roadway width, curve length, ADT, presence of a spiral, superelevation, and roadside condition. Curve flattening is expected to reduce accidents by up to 80%, depending on the amount of flattening. Widening lanes or shoulders on curves can reduce curve accidents by as much as 33%, while adding spiral transitions on curves was associated with a 5% accident reduction. Improving deficient superelevation can reduce accidents by 10% or more, while the effects of specific roadside improvements were also quantified. An economic analysis was conducted to determine when curve flattening and/or widening are cost effective. (Author/publisher)
Samenvatting