traffic Management

Tunnel refurbishment or upgrading may require:

• total closure of the tunnel during the entire duration of the works,
• total closure of the tunnel during periods of low traffic (nights, weekends….),
• partial closure of one direction for a single tube tunnel or one tube for a twin-tube tunnel, potentially with alternate traffic
• partial closure of one or several lanes in the tunnel (in one direction or in one tube).

If possible, total closure of the tunnel for refurbishment/upgrading is strongly recommended during the entire duration of the works as it undeniably provides the best solution in terms of safety for both workers and users. When possible, it is better to implement closures over short periods and during low traffic (night, weekends etc.).

However, these two solutions mean that a deviation route becomes obligatory and the impact on a given road network can be considerable, especially in urban areas.

Depending on local circumstances, the traffic diversion route may be very long. The risks and costs of a long detour over a short period must be balanced against the risks and costs of a partial tunnel closure over a longer period. It is possible to calculate the costs of detours, including the extra kilometres and delays, to back-up and/or support a decision. Any planned closures must be coordinated in advance with the operators of the roads used for rerouting traffic.

If it is technically possible, if the traffic is low and diversion roads are not practical, an alternate traffic system may enable the tunnel to remain open.

In the event of closure, good advance preparation is essential and can significantly reduce disruption. Regional and/or nationwide publicity in advance of the closure is important (e.g. television, radio, internet, billboards, publication of telephone numbers for information and complaints).

Once the tunnel is closed, diversion signs and signals should be used 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. For users who are relatively close to the tunnel, they must be informed of the closure and the alternative route before the last point of choice.

When it is inevitable that refurbishment/upgrading work must be carried out while traffic is present, specific traffic management measures must be adopted upstream from and inside the tunnel. In tunnels with two or more tubes, it is possible to close a tube completely and either establish bi-directional traffic in the other tube or establish a deviation route for users of the closed tube. If bi-directional traffic is established in the other tube, there is less inconvenience to users, as they do not have to take a deviation route. However, in terms of safety, this solution is far from ideal (and should be avoided in heavily trafficked tunnels) since it leads to users driving in opposing directions and hence an increased risk of accidents. This risk 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 as a buffer safety zone. Additional traffic management measures such as speed limit reductions and the implementation of an obligatory distance between vehicles should also be envisaged.

Where a tube is not completely closed to traffic and simple lane closures are implemented, they should always start before the entrance portal. Traffic should first be merged into the slower moving lane, then moved to the lane available at the incident site before entering the tunnel. In urban tunnel approaches this may not always be possible. Preferably lane closures should run for the full length of the tunnel. A situation where traffic is required to change lanes inside the tunnel is generally not recommended. However, in the case of longer tunnels, it may be advantageous to allow traffic to diverge and use all lanes once clear of all of the work sites. A risk assessment can result in the safest method for the situation.

Once again, additional traffic management measures such as speed limit reductions and the implementation of an obligatory distance between vehicles should also be envisaged.

Addition information on traffic management measures during tunnel closures can be found in PIARC report 2008R15EN: “Urban Road Tunnels: Recommendations to Managers and Operating Bodies for Design, Management, Operation and Maintenance”.