The large majority of road tunnels have no emergency lane. This creates a likelihood that tailbacks can occur - depending on the traffic intensity, the presence of broken down vehicles or other problems causing drivers to stop. According to some German and French statistics, tunnels without emergency lanes are less safe than tunnels with emergency lanes (see Technical Report 2008R17: "Human factors and road tunnel safety regarding users").
Lay-bys allow vehicles to stop in a tunnel without blocking the carriageway.This reduces traffic disruption and the risk of a collision.It is easier and safer for the occupants to get out of their vehicle in a lay-by, for example in order to use an emergency telephone.The shelter from traffic can be particularly beneficial for disabled drivers.Lay-bys are also very important for the maintenance of the tunnel and ensure the safe parking of the maintenance vehicles.
The distances between lay-bys vary from tunnel to tunnel. In some national guidelines these distances depend on the classification of the roads the tunnels form part of the Technical Report 1995 05.04.B "Road safety in tunnels" noted that their utilisation rate was generally low. In tunnels with lay-bys, only 20% of faulty vehicles stopped in a lay-by.Recommendations were given to improve this.
In longer tunnels, facilities may also be provided to allow vehicles to turn around or cross into an adjacent tube.These could be useful for maintenance, for manoeuvring emergency vehicles during an incident, or for traffic management following an incident.More specifically, some countries provide turning bays for vehicles. This is because, although cars and vans can turn easily at standard lay-bys, heavy goods vehicles and buses require more space. These turning bays usually measure 4 m by 17 m or larger (see the Technical Report 1999 05.05.B: "Fire and Smoke Control in Road Tunnels" ). When they are provided, they should be located every 1-2 kilometers.