Current procedures for setting ramp advisory speeds in the state of Texas are outlined in the Texas Department of Transportation’s official procedures for establishing speed zones. For ramps, these procedures suggest using exit speed or ramp speed signing where an engineering investigation shows the necessity of advising drivers of the maximum recommended speed on a ramp. Research conducted under this investigation involved speed studies of ramps with a broad range of horizontal and vertical curvatures, frontage road to freeway speed differentials and distances between the ramp and the downstream cross street in order to create a predictive model of ramp speed. Utilizing the degree of curvature (if any) found along the ramp and the distance along the ramp from the freeway exit ramp gore to the downstream intersection along the ramp or frontage road, analysts use the predictive model to identify the expected mean truck speed along the ramp. Based on the difference in speed between the freeway and the mean truck speed expected along the ramp, a ramp advisory speed signing scheme is recommended. (Author/publisher)
Abstract