Offtracking is the term used to describe the difference in path radii between the leading and trailing axle of a vehicle as it maneuvers around a turn. This phenomenon probably has been observed from the time multi-axle vehicles first were constructed. As vehicles, particularly articulated trucks, have become larger and longer, and the urban environment has become more compact and crowded, practical safety concerns relating to offtracking have increased. The geometric design of streets and highways, and of parking lots and trucking yards, will be affected by the maximum offtracking of vehicles using those facilities. In some accident investigations, offtracking is a primary consideration.
Much of present offtracking analysis is based upon a “zero-speed” assumption. In other words, the magnitude of offtracking is computed simply as a kinematic problem, with no dynamic effects considered. When the problem is analyzed kinetically, offtracking outside the path of the preceding wheels (a kind of “oversteer”) can be computed, depending on vehicle speed and configuration. Effects of roadway superelevation and other three-dimensional terrain features can be included in computer simulations.
This paper summarizes the history of offtracking analysis, presents a review of calculation methods in the literature, and details the speed-dependent nature of offtracking for two articulated heavy trucks, utilizing three-dimensional computer simulation.