Abstract
A simplified analysis is made of the directional stability of vehicle combinations, such as a tractor combined with one or two semitrailers or a truck and full trailer. Vehicle combination are treated as linear dynamic systems with two-degrees-of-freedom for each unit. The equations of motion are derived considering the influence of braking and acceleration, and a characteristic equation for travelling at constant speed is obtained. The Routh criteria are examined to distinguish between stability and instability, considering oscillatory and periodic motions separately. Special attention is given to the behaviour of the vehicle during braking with discussion of the influence of various.