EFFECTS OF EXPRESSWAY RAMPS ON CONTROL OF TRACTOR-SEMITRAILERS

An overview is provided of the study methods, findings and recommendations of a 3-year study to establish how particular expressway ramps cause drivers of tractor-semitrailers to lose control of their vehicles. The study selected a set of problem ramps, and put the geometric details of each ramp into a computer simulation program, and then simulated the dynamic behavior of tractor-semitrailers traversing the ramp and responding to its geometric properties. It was found that highway design in the U.S. does not take sufficiently into account the special maneuvering limitations of heavy trucks. The most fundamental of those are low resistance to rollover and poor braking capability. Additional problems and other aggravating conditions are also noted. It is recommended that all AASHTO (American Association of State Highway and Transportation Officials) policies relating to the geometric design of highway ramps and other curved roadways be examined from the viewpoint of the maneuvering requirements of heavy trucks. It is also recommended that truck drivers be better informed about the hazards associated with expressway ramps. A training film for truck drivers is noted.