Civil and Environmental Engineering



Ronald K. Faller

Document Type


Date of this Version



Published in Journal of Transportation Safety & Security 6:4 (2014), pp. 356–368.


Copyright © 2014 Taylor & Francis Group, LLC and The University of Tennessee

doi: 10.1080/19439962.2014.887597


The benefits of slope flattening were investigated by simulating accident costs with updated foreslope severities based on real-world accident data collected over a 7-year period in the State of Ohio. Functional classes considered were freeways, rural and urban arterials, and rural and urban local highways. Highways were modeled using the Roadside Safety Analysis Program (RSAP). Highway parameters considered in RSAP were slope steepness, roadway curvature, percent grade, longitudinal length, fill height, and lateral offset to the slope break point. Simulated accident costs were incorporated into a Microsoft Excel spreadsheet, where future users can specify installation costs, which tend to vary significantly from one location to another for slope flattening applications. Each functional class demonstrated slope flattening trends. On freeways and urban arterial highways, slopes should be no steeper than 1V:3H, and the benefit of flatter slopes was minimal. On rural arterial highways, the slope should be no steeper than 1V:4H, and the benefit of flatter slopes was also minimal. On local highways, the steepest slope should be 1V:3H, but the slope should be made as flat as possible because accident costs continued to decrease as the slope was flattened.