Besides monitoring compliance with regulations on commercial vehicle weight, weigh-in-motion (WIM) devices provide detailed data that are very useful for analysing characteristics of road freight traffic and HGV driver behaviour [1, 2]. This paper presents results on HGV spacing and silhouettes on a French motorway. Detailed, anonymised data from WIM devices on the A63 motorway (illustration 1) were provided by the French Centre of Studies and Expertise on Risks, the Environment, Mobility and Planning (Cerema) to the motorway concession-holder, Atlandes. This work was prompted in part by a preliminary study for planned platooning trials. It provides explanations concerning HGV flow that could help enhance road safety through more detailed analysis of road traffic on the road infrastructure.