This paper describes varoius aspects of the long reduced-height road tunnels that are being used in France to reduce traffic congestion in major courbations. These tunnels are typical between 500m and 10 km long. Reasons for using type of tunnels include: the very high proportion of low vechiles in urban traffic, their technically easier construction, due to their smaller cross section, the acceptability of steeper grandients than for tunnels carrying heavy vechiles, their good traffic flow conditiond and their suitability for use in traffic control systems.

In designing these tunnels, the following choices are critical: reference speed, typically 60kph or 80 kph, traffic control operating method and tunnel height, typically 2.00m, 2.70m or 3.50m.

The main features of their geometrical design concern: horizontal and vertical alignment and cross section, including height and widht.

An analysis must also be performed, to design the connections between the main tunnle and its entrances and exits. It takes account of: minimum recommended outdoor configurations and actual vehicle speeds in exchange zones and how to reduce them.