REDUCED HEIGHT URBAN TUNNELS GEOMETRIC DESIGN
1995
This paper describes various aspects of the long reduced-height road tunnels that are being used in France to reduce traffic congestion in major conurbations. These tunnels are typically between 500m and 10km long. Reasons for using this type of tunnel include: (1) the very high proportion of low vehicles in urban traffic; (2) their technically easier construction, due to their smaller cross section; (3) the acceptability of steeper gradients than for tunnels carrying heavy vehicles; (4) their good traffic flow conditions; and (5) their suitability for use in traffic control systems. In designing these tunnels, the following choices are critical: (1) reference speed, typically 60kph or 80kph; (2) traffic control operating method; and (3) tunnel height, typically 2.00m, 2.70m or 3.50m. The main features of their geometrical design concern: (1) horizontal and vertical alignment; and (2) cross section, including height and width. An analysis must also be performed, to design the connections between the main tunnel and its entrances and exits. It takes account of: (1) minimum recommended outdoor configurations; and (2) actual vehicle speeds in exchange zones and how to reduce them.
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