Using naturalistic driving study data to explore the association between horizontal curve safety and operation on rural two-lane highways

Abstract

Horizontal curves are associated with a disproportionate number of severe crashes, particularly on two-lane rural highways. Many efforts have been placed to improve curve safety and efficiency; however, in many previous studies the curve safety and operational characteristics were analyzed separately. With the development of the Second Strategic Highway Research Program (SHRP2), greater data resources have become available to the analysts. The main objective of this study is to assess the curve severity and crash rates at horizontal curves using both the operating characteristics and safety data simultaneously. For this purpose, this study used the SHRP2 Roadway Information Database and Naturalistic Driving Study data to obtain the curve operating information and geometric features and merge them with eight years of crash records. Then, this study calculated the severity of each curve using four methods and compared the curve severity with the severity based on crash rates. The results of the computational analysis suggest that for the higher curve severity categories, curve severity (which is related to side friction demand and tolerance) is positively correlated with crash rate. Safety analysts and roadway agencies are recommended to consider using SHRP2 data and curve severity assessment methods for improving the safety of horizontal curves.