Tunnel safety on motorways
In Dutch motorway tunnels, the crash rates are more than three times higher than those on the open motorway. The most important factors that increase the crash rate in tunnels are the proximity of the tunnel wall due to a lacking emergency lane, the tunnel slopes and the resulting speed differences, the transition from light to darkness especially while entering the tunnel, and pieces of road side brackets on the road broken off by lorries. Road works can further increase the danger if traffic in both directions is being led through only one of the tunnel tubes when the other is closed down.
A tunnel crash generally has more serious consequences than a similar crash elsewhere on the motorway. In addition, a tunnel incident can also indirectly affect other road users, for example by fire or smoke.
Measures to improve tunnel safety are aimed at the crash rate-increasing factors. The presence of an emergency lane reduces the optical narrowing of the tunnel entrance. Especially lorries tend to swerve towards the middle of the road if there is no emergency lane. It is important to ensure a gradual transition from natural to artificial light so that the road user's powers of perception remain intact. Furthermore, exit and joining lanes and weaving segments should not be situated near the tunnel entrance or exit.
For more details: Fact sheet The road safety in motorway tunnels (pdf)