Signs used to manage traffic inside tunnels may be fixed or dynamic.
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 left or right. 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.