It has been attempted to develop geometric design standards to accommodate low-ground-clearance vehicles using computer software. Low-clearance vehicles include lowboy equipment trailers, car carriers, single- and double-drop van trailers, and cars and trucks with trailers. Hang-ups and overhang dragging on high-profile roadways are causes of concern for low-ground-clearance vehicles. The objective was achieved through the development and application of the HANGUP software package and the analysis of the design standards of several agencies. Although a few agencies have developed geometric design standards for low-clearance vehicles at rail-highway grade crossings, they are not commonly used by highway engineers. The American Railway Engineering Association (AREA) grade crossing and ITE driveway design standards were evaluated with HANGUP using a vehicle with a 36-ft wheelbase and 5 in. of ground clearance. This can be considered as the standard or "design" low-clearance vehicle. On the basis of limited field data collection, such vehicles represented 85th-percentile values for ground clearance and wheelbase. The results indicate that the AREA design standards accommodate low-clearance vehicles but the ITE standards do not. Grade changes of more than 2.3% on each side of railroad grade crossings have the potential for causing low-clearance vehicles to become stuck. Grade changes at intersections should be less than or equal to 4.6%, which is the maximum slope rate for the standard low-clearance vehicle.
Abstract