Abstract: A sensor array which extends only over a fraction of the length of the vehicle generates pick-up signals in response to signals emitted by a ground wire lying in the ground. The pick-up signals are processed in signal-processing circuits to generate a heading signal and a displacement signal representing the position of the vehicle and the direction of its longitudinal axis relative to the guide wire. A curvature detector is provided for generating a curvature signal, which represents the curvature of a bend of the guide wire near the sensor array. The heading, displacement and curvature signals are combined by a signal-combining circuit, which delivers a position control signal to position control means for controlling at least one steerable wheel of the vehicle so as to steer the latter along the guide wire.