In major urban areas the part of light vehicles in the road traffic is about 90%. Whenintended to free the surface streets from traffic by building an underground it may bevery useful to reserve a tunnel to these light vehicles. The heavy goods vehicles caneither use the surface streets or use another tunnel. This solution was selected for thecompletion of the West Paris A86 ring motorway in Versailles. The tunnel reserved tomaximum 2 m-high light vehicles will have a 11.10 m excavated diameter. It will beshield driven. It will include two superposed traffic levels, each of them with 3 trafficlanes, including one for entrance and exit. The length will be 10 km.The heavy goods vehicles will use another tunnel of similar diameter, including onelane per each direction, therefore of conventional type. Then cost savings concern theglobal construction costs; underground entrance and exit are possible via highgradient underpass approaches (12%), thus preserving the surface street network.Lastly, the tunnel will be a very safe structure, without cycles or heavy goods vehicles.The works will start in 1997.This concept of long, reduced height tunnel was extended to other categories ofpermitted gauges (2.70 m and 2.50 m), also to various control levels of operatingconditions, related to more or less broad usable widths. They can be applied to allexcavation or construction modes (excavated or shield-driven tunnels, or cut-andcovers).This led to recommendations for reduced height urban tunnels produced bythe French Ministry of Public Works (Directorate of Roads - Tunnels Design Centre).The number of tunnel projects reserved to light vehicles is increasing in France. WestA86 will be the first large project of this series.
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