Landing Forces Resulting from Exiting Tractors and Trailers

Tractors are generally provided with step and grab rail systems to facilitate driver entrance and exit from the cab. However, many of these systems are not designed based on human factors engineering principles, particularly anthropometry and thus are not always used. Some examples include steps or rails that are too high for a cross-section of the population to reach or steps that are difficult to see as the occupant descends from the cab. Trailers frequently do not have any “designed steps/grab rails” to aid the driver or material handler in safely climbing up or down from the rear of the unit. As a result, squat jumping from the trailer floor down to the ground is a common method of exit from commercial trailers. Injuries resulting from exiting commercial vehicles could represent a substantial cost to businesses operating these equipment. The purpose of this study was to quantify landing forces experienced during various tractor and trailer exit methods ranging from making optimal use of hand rails and steps to jumping. The study investigated landing forces sustained by ten male subjects while exiting two tractors and a box trailer. Steps were retrofitted onto the back of the box trailer in order to show reductions in landing forces achievable from trailers that are retrofitted with improved access systems. The results showed squat jumping down from the back of a box trailer generated landing forces as high as 11 times body weight. On the other hand, using the trailer's retrofitted step and grab system while exiting resulted in landing forces reduced by over 66%. Jumping from the cab-level of a cab-over-engine tractor resulted in landing forces as high as 12 times the subject's body weight; whereas, fully utilizing the existing steps and grab-rails kept the landing forces under two times their body weight. An approach that emphasizes optimal entry/exit aids design based on human factors engineering, coupled with driver training is expected to minimize vehicle-related musculoskeletal injuries.