Distribution of Roadway Geometric Design Features Critical to Accommodation of Large Trucks

Abstract

The ability of the roadway system to accommodate large trucks is constrained by the geometric design of key features, including horizontal curves, interchange ramps, interchange ramp terminals, at-grade intersections, and steep grades. The distribution of the dimensions of roadway elements that are critical to accommodation of larger trucks on the highway is shown, including horizontal curves and grades on mainline roadways, horizontal curves on interchange ramps, and curb return radii for at-grade ramp terminals and intersections. Frequency of mainline and ramp curves with very sharp radii and of very steep mainline grades was found to be very limited. For example, only about 5 percent of interchange ramps have horizontal curves with radii of 30 m (100 ft) or less, and approximately 20 percent of rural ramps and 30 percent of urban ramps have radii of 75 m (250 ft) or less. Curb return radii less than or equal to 12 m (40 ft) on which trucks would frequently encroach are more frequent. Curb returns with sharp radii are more prevalent in urban than in rural areas and are more prevalent at intersections than at ramp terminals.