The knowledge of heavy vehicle traffic on the road network plays a key role for transport policy and road operators to : - increase the mobility by adapting the policies, - improve road safety, - reduce unfair competition between transport modes and companies, - optimise infrastructure lifetime, and thus to ensure weights and dimensions compliance and to enforce the traffic regulations. Since 2008, 29 WIM systems were installed for the French Ministry of Transport on the main road network, i.e. highways and motorways. They continuously screen overloaded and speeding vehicles and allow to target the controls on presumed violators. The check efficiency was increased by a factor 3, and the accuracy of the WIM systems now allows envisioning the future development of an automated overload control (AOC) system. These systems also allow profiling companies which are frequently infringing the driving law and to target the checks in companies. Detailed heavy traffic data are gathered on a large scale, both as classified flows (statistics), and individual data per vehicle. These data are stored in a National database, and used for statistics, for infrastructure design and management, and for traffic monitoring. Examples of application to pavement and bridge assessment are presented.