In this thesis the lateral performance of heavy vehicle combinations, specifically longer combination vehicles, is discussed. The use of longer combination vehicles is promoted by their positive impact on the traffic congestion problem, as well as their economic and environmental benefits due to reduced fuel consumption and emissions. However, from a safety perspective, there are concerns about their impact on the traffic. In a heavy vehicle combination maneuvering at high speeds, lateral motions get amplified at the towed units, which causes trailer swing and large path deviation and side slip. These amplified motions are dangerous for any nearby cars as well as the vehicle combination itself and can lead to instability. The main goal of the research presented in this thesis is to develop control strategies for improving the lateral performance of heavy vehicle combinations at high speeds by suppression of amplified motions at the towed units. As a starting point, the heavy vehicle accidents are investigated and the relevant critical maneuvers are identified. Subsequently, the lateral performance of heavy vehicle combinations in the identified critical maneuvers is investigated by simulations to obtain a better understanding of the causes behind rearward amplification of motions in heavy vehicle combinations and to specify the control objectives. Accordingly, a generic controller for improving the lateral performance of heavy vehicle combinations by active steering of the towed units is developed. The developed controller is verified for various heavy vehicle combinations by simulation, with respect to the identified critical maneuvers. The verification results confirm the effectiveness of the controller and show significant reductions in yaw rates, side slip and path deviation of the towed units of the heavy vehicle combinations, up to 70%. Additionally, the robustness of the controller is evaluated by extensive analysis of its performance in various driving conditions and presence of parameter uncertainties for a sample heavy vehicle combination. Furthermore, the controller is implemented on a truck‐dolly‐ semitrailer test vehicle and verified in a series of single and double lane changes. The experimental results approve the simulation outcomes. The developed controller can be easily implemented on steerable trailers; since it utilizes common sensors for steering input, speed and yaw rates and does not require large computing capacity. The significant improvements obtained by the developed controller can promote the use of longer combination vehicles in traffic, which will result in a reduction of traffic congestion problem, as well as substantial environmental and economic benefits.