Using the hard shoulder and narrowing lanes to reduce traffic congestion some lessons from an experience on the Paris motorway network

Increasing congestion on the motorway networks has led the decision-makers to test innovative practices of road use. Various methods are being experimented to control this congestion and to increase the capacity of the existing infrastructures. The first one is to reserve the use of some lanes to specific categories of vehicles or users. Other more recent techniques can, under certain conditions, increase the number of lanes through a new definition of the cross section or through the use of the hard shoulder as an auxiliary lane. Lane management is a concern shared by many operators. In several European countries, the best use of the infrastructure is a priority and a privileged theme of investigation. These new practices are the subject of debates and raise legitimate questions on the real impact of the schemes implemented. What are the effects of reducing the lane width and using the hard shoulder on the capacity and the level of service? This paper provides elements to reply to the above. It is based on the real case of the new design of the A3-A86 trunk road in the Paris region. A comparison has been made between a reference situation with 4 lanes and a hard shoulder and a new configuration with 5 lanes without the hard shoulder. The evaluation summarises the impact of the new cross section on capacity, level of service and the evolution of traffic congestion.