Improved CAD Application for Low Speed Vehicle Turn Simulations

The provision of adequate vehicle maneuvering space is an important requirement in the design of roadway intersection and other similar transport facilities. Typically these vehicle maneuvers are performed at low speeds, generally less than 15 km/h. Until recently, transportation engineers have relied on simplistic plastic vehicle turning templates or outdated computer models to verify the turning paths of design vehicles. Such methods and tools have several disadvantages and drawbacks, the most important being their limitations, accuracies and integration with widely used CAD systems. Further, AASHTO and other design guidelines make limited reference to realistic driver behavior and appropriate drive paths for low speeds vehicle maneuvers. This paper describes a CAD based vehicle simulation model that incorporates a steering rate factor that provides a more realistic model. This factor was obtained through a variety of field tests that were performed to study driver behavior. The tests involved measuring predefined semi-trailer maneuvers using manual and GPS systems to gather precise driver behavior. The results from these tests provide additional insights into low-speed vehicle maneuvers, not readily available in design guidelines such as AASHTO. With this model, better design solutions can be achieved for facilities accommodating low speed vehicle turn maneuvers.