United States Department of Transportation
i
Horizontal Curve Safety Performance Evaluation Based on the Naturalistic Driving Study Lane Position Data
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2024-05-01
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[PDF-1.38 MB]
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Edition:Final Report
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Abstract:Geometric design based on performance is a renewed approach to project decision making that specifically addresses the purpose and needs of projects by providing design flexibility. Transportation practitioners need resources to evaluate roadway design based on safety performance. This research project used the Roadway Information Database and the Second Strategic Highway Research Program Naturalistic Driving Study data to estimate the safety effect of elements that influence driving behavior on rural, undivided, two-lane horizontal curves (Iowa State University 2024, Virginia Tech Transportation Institute 2023). Available data included 3,292 curves and 150,233 traversals, which required a significant data processing effort to conduct data cleaning and quality assessment. From the safety surrogates evaluated and methods implemented, lane position provided the most consistent and statistically significant results. The researchers modeled centerline and edge-line encroachment events with the negative binomial regression modeling approach, using curve geometry as the predictor component. Encroachment estimates were associated with observed crashes from State data to convert encroachments to crashes. Predictor variables, such as curve radius, showed a decreasing trend in predicted crashes as the curve radius increased. Similarly, as shoulder or lane width increased, predicted crashes decreased. The researchers used crash estimates derived from safety surrogates to develop an analytical tool aimed at practitioners designing curves (University of Wisconsin–Madison 2024). Data input in the tool includes curve radius, shoulder width, lane width, length, annual average daily traffic, construction cost, and expected service life. The economic assessment provides a quantitative measure for practitioners to evaluate implementing alternative curve designs by assessing the tradeoffs between safety and implementation cost.
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