Assessment of Interaction of Crash Occurrence, Mountainous Freeway Geometry, Real-Time Weather, and Traffic Data

Transportation Research Record: Journal of the Transportation Research Board, No. 2280, Transportation Research Board of the National Academies, Washington, D.C., 2012, pp. 51–59. DOI: 10.3141/2280-06 Department of Civil, Environmental, and Construction Engineering, University of Central Florida, 4000 Central Florida Boulevard, Orlando, FL 32816-2450. Corresponding author: M. M. Ahmed, [email protected]. system, which is mainly used for toll collection and to estimate travel times along freeways. Traffic data collected from different detection systems, such as inductive loop detectors, were proven by several studies to be useful for real-time safety risk assessment (1–10), and one study by the authors investigated the usefulness of the traffic data collected from AVI systems in real-time safety assessment (11). The Colorado Department of Transportation developed the COTrip system to provide travelers with important information about travel time, congestion, adverse weather conditions, and lane closures due to occasional avalanche danger, maintenance on the road, or road crashes. This information is provided as a part of an intelligent transportation system and can be accessed through a website. In addition, the real-time information is dynamically disseminated to road users via dynamic message signs. This system estimates the travel time on a segment by monitoring the successive passage times of vehicles equipped with electronic tags at designated locations. AVIs measure space mean speed, which is the harmonic mean of the speed of all vehicles occupying a given stretch of the road over some specified time period. In previous studies, weather data were estimated from reports for crash cases and from the weather stations of airports in the vicinity of the freeway section for noncrash cases (12, 13). None of these studies, however, had access to actual weather information on the roadway section itself. In this study, real-time weather data were gathered by weather stations installed on the roadway solely for the purpose of collection of real-time information about adverse weather conditions. Moreover, roadway geometrics were considered in a few studies (6, 14), and their effects were controlled for by a matched case– control framework in other studies (2–9, 11, 12). These studies were mostly conducted on freeways or expressways that feature normal roadway geometries, and therefore, the traffic flow parameters were found to be the most dominant factors that contributed to crash occurrence. Because the roadway section under study features mountainous terrain with relatively steep grades and sharp horizontal curves, the geometric characteristics were considered to examine how the interaction between all these factors contributes to crash occurrence. This paper investigates the identification of freeway locations with high crash potential with traffic data collected from an AVI system, real-time weather information, and data on geometric features. Assessment of Interaction of Crash Occurrence, Mountainous Freeway Geometry, Real-Time Weather, and Traffic Data