Why do curved tunnels need clearance widening?

Tunnel curve widening is due to the vehicle in the form of the process of turning, the vehicle bogie running along the track, but the vehicle itself (each car) can not be bent, in order to avoid certain parts of the vehicle out of the limit, set up in the curve section of the widening, the general radius of the curve does not need to set up widening.

Because the vehicle itself but can not bend with the line, still maintain the rectangular shape of the vehicle vehicles through the curve, the center point of the bogie running along the line, the role of centrifugal force caused by the train to the outside of the rails to move, and some freight trains are equipped with overloaded goods, so the railroad curve tunnel to widen.

Railway tunnel headroom

Railway tunnel headroom single-line railroad tunnels in order to match its equipment have different standards. However, in a straight interval track, single and double line tunnels should not be less than the standards shown in Figure 1.

In railroad tunnels, if there is no shelter on either side, then personnel access needs to be provided in the headroom. This type of clearance should be at least 6ft8in or 2m high, with a minimum width of 30in on each side in the vehicle limit diagram, although 24in is used as a minimum on some lines. In road tunnels, a kerb clearance of 3ft or 0.9m is used for pedestrian access.

Reference: Baidu Encyclopedia-Tunnel Building Limits