The influence of self- and forced-steering axles on the directional dynamics of a tractor-semitrailer is investigated through computer simulations. The dynamic characteristics of a self-steering axle are analytically modeled and integrated to a three-dimensionalnonlinear directional dynamic model of the vehicle. Two forced-sleering algorithms relating !he vehicle speed and response quantities to the angle of the wheels of the steerable axle are formulated. and integrated to the nonlinear directional dynamic model of the vehicle. Computer simulations are performed to determine the directionalresponse characteristics of a tractor-semitrailer with self- and forced-steering axles for low as well as high speed maneuvers. The directional response characteristics of the vehicles with self- and forced-steering axles are discussed in view of the self-steering parameters and forced-steering gains, and compared to those of the vehicle with conventional axles.