Cross-Sectional Study of Vehicle Speeds on Rural Four-Lane Highway Curves

Abstract

Research has consistently shown that horizontal curves are often associated with increased crash rates compared with similar tangent highway sections. These crashes are often related to speed and the difficulty of judging the severity of the curve. Curve speed models are used for a variety of applications, including assessing operational characteristics, evaluating design speed, conducting spot safety analyses, and setting curve advisory speeds. However, most of the documented curve speed models apply to rural two-lane highways, while relatively few models have been developed for rural multilane highways. These types of highways may exhibit different driver behavior in curves because of their more generous geometric design and higher traffic volumes. The objective of this paper is to document models that have been developed for several types of rural four-lane highways, including undivided highways, divided highways, and freeways. The authors developed models that account for geometric characteristics like curve radius, superelevation rate, and deflection angle, as well as operational characteristics like approach tangent (TN) speed. These models were calibrated using a database of about 46,000 vehicles across 29 horizontal curve sites in central Texas.