The aim with this investigation was to study the aerodynamic properties of truck-trailer combinations of varying lengths. The aerodynamic properties of the combinations were evaluated in order to study similarities and differences in the flow field between different configurations. By the use of Computational Fluid Dynamics (CFD) six different types of truck-trailer combinations used for long hauling have been evaluated. The combinations have a total length varying between 10.10 m and 25.25 m and consist of either a tractor or rigid truck in combination with one or two cargo units. All of the combinations are commonly found on roads in Sweden and several other countries in Europe.The results from the simulations show that the aerodynamic properties differ significantly for the truck-trailer combinations. It was found that the longer vehicle combinations are much more sensitive to yaw conditions than the shorter combinations. What was also evident is that the gap between the first and second cargo unit plays a significant role for the aerodynamic properties. Furthermore it was established that there is potential for fuel saving by a strategic choice of truck-trailer combination. According to the simplified evaluation made in this study the 25.25 m combinations show a lower power required per loading length (LL) and are therefore shown to be more efficient than the shorter combinations.