NEW METHODS FOR DETERMINING REQUIREMENTS FOR TRUCK-CLIMBING LANES. SUMMARY REPORT

To facilitate traffic flow and to improve highway safety on upgrades, highway design engineers have constructed hill-climbing lanes. A recent FHWA-sponsored study found that current guidelines may be leading designers to overdesign highways, adding and maintaining unnecessary hill-climbing lanes. The report summarized here highlights four major findings of the earlier FHWA study: (1) current design guidelines are conservative for single-unit trucks and tractor-semitrailers and current critical lengths of grade are thus shorter than these two truck types would warrant; (2) single-unit trucks with trailers and doubles do not perform nearly as well as single-unit trucks and tractor-semitrailers, which may indicate that the performance of the latter two types of trucks match current guidelines; (3) critical length of grade should be based on the weight-to-available power ratio of current truck mix, rather than on assumptions about the performance of a 300-lb/hp truck which was typical in 1965; and (4) highway designers need more comprehensive methods for deciding when hill-climbing lanes are warranted. This report also presents tools developed in the study for designing hill-climbing lanes. This report was based on the following study: "Methods for Predicting Truck Speed Loss on Grades - Final Technical Report: FHWA/RD-86-059."