To manage the traffic and provide users with more comfort, a large variety of equipment can be installed inside the tunnel. Signs and signals are some of the main devices available to the operator to perform this task.
For a given type of road, tunnels have the same signs and signals as in open air:
The means available to the operator to manage the traffic on the route where the tunnel is located and inside the tunnel include:
This equipment could be located inside the tunnel, but also at the entrance to the tunnel and (if possible) at a distance sufficient for the user to be able to be diverted to an alternative route, if necessary. The main problem with regard to signage within a tunnel relate to the geometrical characteristics which must be optimised. Increasing the cross section will lead to significant extra costs. In practice, a compromise must be found between the need for good visibility of the signs (which must be sufficiently large) and the space available.
The different safety devices available to tunnel users (emergency telephones, extinguishers, emergency exits...) require additional specific safety signage (see page Monitoring and Incident detection and Evacuation aids).
Fig 1. Example of dynamic lane allocation signs (Singapore)
Fixed signs may indicate the usual speed limit, that overtaking is prohibited or the distance to be respected between vehicles. Other fixed signage that is specific to the tunnel environment indicates the different safety facilities or devices available to tunnel users (such as, lay-bys, emergency stations with emergency telephones, extinguishers).
In the event of an accident or breakdown, dynamic signs may be used to communicate important information to the users and to manage traffic. Lane allocation signs, positioned above the carriageway indicate which lanes are open and may indicate to users that they need to merge either to the or . Dynamic speed limit signs can inform users of modified speed limits. Variable message signs can be used to inform tunnel users of the nature of the incident and indicate the appropriate behaviour to adopt (slow down, stay in lane, etc)
If a traffic incident involves a fire requiring the evacuation of users, in addition to evacuation messages displayed on VMS, specific signs indicate the evacuation route leading to emergency exits.
All signs should be designed and positioned so that they are clearly visible and easy to read. Signs should include a relatively short text or message so that they can be easily read by motorists. In practice, a compromise must be found between the need for good visibility of the signs (sufficiently large panels) and the space available.
Figure 1: Approach signs on the run up to a tunnel in Austria
Approach signs that provide a warning to drivers of the authorised vehicle height may be included into a height restriction device (Fig. 2).
Figure 2: Height restriction signs and barriers on the approach road to a tunnel in Austria
Signs located near tunnel portals mostly indicate certain restrictions/mandatory behaviour with regard to the use of the tunnel.
Fig.1: Regulatory signs grouped together onto a single sign at the Mont Blanc tunnel portal
Typically, regulatory signs at portals are used to indicate:
These regulatory signs can sometimes be grouped onto a single sign as given in Fig. 1.
Certain countries have a specific « tunnel » sign to which some of the above-mentioned information is added.
Information signs are usually also located near the tunnel portal, providing:
Figure 2: Signs at a portal showing the length of the tunnel and the distance to be kept between vehicles
For tunnels with a height limit that is lower than that of the access road, there is also a sign indicating the maximum authorised height. This sign may also be accompanied by a physical obstacle designed to limit the risk of over-height vehicles hitting tunnel equipment.
Figure 1: Sign indicating that the tunnel is prohibited to vehicles with a height over 4.3 metres and that an alternative route must be taken (France).
If they are restricted to certain categories of vehicles (over-sized vehicles, dangerous goods vehicles), alternative routes must be available and clearly indicated as shown in the example below.
If a tunnel is completely closed, due to an accident, road works etc, all users must be informed of the various alternative routes. It is necessary to provide information to users as far upstream as possible, before the relative points of choice, which are sometimes located at a considerable distance from the tunnel. If the tunnel is part of an urban network, other signage means can be used to facilitate the management of diverted traffic (e.g. variable message signs).
Figure 2: Variable message sign indicating a tunnel closure due to road works and the alternative route to be taken (Belgium)
Figure 3: Sign indicating the closure of the Lioran tunnel and the alternative route (France)
Figure 1: A double closure barrier, used in combination with a stop signal and a variable message sign, (France)
When a serious event (accident, fire, etc.) occurs in a tunnel, it must be possible to prevent users from entering as they risk encountering a potentially dangerous situation.
Devices are therefore used to warn users who are outside that the tunnel is closed and/or prevent them from entering.
In many countries, experience shows that if the tunnel is closed simply by means of a stop signal placed in front of the entrance, it is not always effective.
Therefore, this stop signal is often combined with barriers and variable message signs, allowing the users to be informed of the reasons for closure (Fig.1)
Figure 2: Example of a single tunnel closure barrier used in combination with stop signals (Austria)
The tunnel closure device can be activated from the control-command centre or automatically in tunnels that are not monitored continuously. Some road authorities also mandate that a ground responder has to be deployed at the tunnel entrance before the barrier can be safely lowered.
The closure device is meant for use in emergency situations but it can also be used in other situations, particularly during scheduled closures for maintenance interventions.