Date of this Version
MwRSF Research Report No. TRP-03-269-14
Phase I of this project relied on assumptions surrounding crash data from the state of Ohio in 2000. The number of fatal and severe crashes in that year was significantly lower than average. As a result, the conclusions were indefinite. Phase II was carried out using crash data from the state of Ohio over seven years. The increased pool of data removed the need for many of the underlying assumptions used in Phase I and provided a solid foundation of conclusions and recommendations.
The number of fatal and severe crashes that occurred on each slope and height for each functional class was calibrated with the Roadside Safety Analysis Program (RSAP), an encroachment-based probability tool, to modify default severity indices for each foreslope and embankment height. The results of the simulations using RSAP were then studied until equations were developed to relate the severity index to the foreslope rate, embankment height, and functional class.
Using the impact frequencies determined by RSAP and the modeled severity indices from the equations developed from RSAP, the deterministic program, Benefit-Cost Analysis of Foreslopes Program (BCAFP), as developed in Phase I, was updated to match the results of the crash data taken between 2000 and 2006. This program allows its user to enter installation costs of various design alternatives, as well as roadway configuration parameters, to quickly and effectively conduct a benefit-cost analysis for use in selecting the most cost-effective roadside geometry. Using the BCAFP program, and based on an existing 1V:2H foreslope, sample guidelines for roadside grading were generated as a function of ADT, road functional class, desired B/C ratio, installation length, slope offset and height, and soil borrow costs.