Safety issues

If the tunnel design and equipment no longer fulfil the requirements of the operator, the tunnel users or legislation, it may be necessary to refurbish and/or upgrade the tunnel.

During refurbishment or upgrading, it is important to:

• maintain a minimum safety level for the traffic,
• ensure the safety of personnel working in the tunnel,

Safety of both workers and tunnel users can be influenced by completing refurbishment/upgrading activities in the shortest period possible and every effort should be made to avoid delays in the progress of work.  Well planned and efficiently implemented works can effectively reduce the length of these periods.

For both tunnel users and workers, total closure of all tunnel tubes during refurbishment/upgrading obviously provides a much higher level of safety. Workers are protected from traffic and teams can work on all facilities throughout the full length of the tunnel. For traffic, accident risks linked to the implementation of temporary traffic control measures within the tunnel are avoided.

In certain cases it is impossible to close the tunnel entirely. For instance, if the tunnel is the only reasonable means of crossing a strait or a mountain ridge, where alternative routes are not possible, not practicable or very expensive. In these cases refurbishment/upgrading of structures and installations have to be performed while the tunnel remains in service.

Partial closure of one or more lanes is possible during refurbishment/upgrading activities, but working in a tunnel while traffic is present is dangerous for the personnel and requires specific measures to protect them (e.g. the construction of temporary barriers to separate workers from the traffic).

In twin-tube tunnels, one tube can be closed for refurbishment while bi-directional traffic flow is allowed in the other tube. However, this solution is far from ideal and should only be adopted if it is not possible to divert traffic onto an alternative route. Whilst it obviously protects the safety of workers, this situation leads to the users driving in opposing directions within a tube where they are accustomed to traffic moving in only one direction. This can induce a potential increase in accident rates and should be avoided in heavily trafficked tunnels. In tunnels with low to moderate traffic, the risk of accidents can be reduced by the use of VMS and overhead lane control signs. In the case of three-lane tubes, the centre lane should, if possible, be kept free of traffic and act as a buffer safety zone.

In all cases where there are plans to alter the usual traffic configuration in a tunnel, additional safety measures should be implemented: reduced speed limit, closure of slip roads in the vicinity of the tunnel and the implementation of safety exercises in collaboration with emergency services under similar “works” conditions.

Finally, each time the lane/tube/tunnel is reopened to traffic following a closure, great attention must to be given to clearing and cleaning the road to prevent accidents caused by tools and materials left in the tunnel or on the road. Similarly, any temporary or uncompleted works must be satisfactorily secured and made safe for the following operating period.

Additional information on refurbishment/upgrading can be found in chapter 6 "Renovation of tunnels" of technical report 05.13.B.