Page:UK Traffic Signs Manual - Chapter 8 - Part 1 (Traffic Safety Measures and Signs for Road). Designs 2009.pdf/71

DESIGN CRITERIA Where it is proposed to close one bore of a twin bore tunnel and use the other bore to operate two-way traffic, the designer should ensure that the tunnel infrastructure and equipment has been designed, or can be added/adapted, to support traffic safely in a contra-flow mode. The temporary traffic management to be provided must guide traffic safely into the temporary two-way running bore whilst preventing an errant vehicle from accidentally entering the closed bore. An access gate or traffic barrier should be considered to control access into the works tunnel site. In addition, if not already in place, the designer should consider the need to provide an emergency means of stopping traffic, such as temporary traffic signals, in the approaches before it reaches the tunnel portals.

Where a tunnel has been designed to permit temporary contra-flow traffic, the traffic management designer should review the tunnel design and operation documentation against the proposed design to establish its current suitability to support the proposed contra-flow operations safely. The temporary contra-flow proposals should be discussed with the tunnel operator/maintainer, the police and other emergency services, and if necessary, the Tunnel Design and Safety Consultation Group (TDSCG) should be reconstituted to endorse, or amend, the proposals before they are incorporated into any specific scheme. Where it cannot be readily established that contra-flow traffic management can be operated and it is not feasible/appropriate to reconstitute the TDSCG, the designer will need to consider the steps set out in paragraphs D3.41.7 to D3.41.9 below.

many road tunnels will have been designed, or subsequently checked, to determine whether, when one bore of a twin tunnel is closed for road works, tunnel maintenance or tunnel refurbishment, the other bore can operate safely. The procedures for maintenance and refurbishment, and also the use of tunnel in a contra-flow condition when appropriate, will be included in the operation and maintenance documents relating to the tunnel. The traffic management designer should consider the adequacy of clearances, see Sections D3.2 and D3.3]. In addition, where these have not already been installed as part of the permanent equipment, the designer may need to consider the provision of lane control signals and VMS signs in the tunnel and at the portal.

Where it cannot be established that contra-flow traffic can operate safely in a tunnel, and work cannot be carried out under lane closures, the affected tunnel traffic will need to be diverted onto pre-planned diversion routes, see Section D315. Temporary traffic diversions may also be required to allow contra-flow enabling works (such as the installation of temporary lighting and ventilation, traffic control signals and signs to be carried in advance of the main works, where these cannot be accomplished with lane closures in low-flow conditions.

For tunnels situated on a dual carriageway road, the design of signs for the approaches to the tunnel portals, lane change, lead-in (crossover), through tunnel (equivalent to works zone) and end-of-works (return crossover) zones are covered in Section D6, for zone definitions, see Section D6.14. Where a tunnel is not already equipped for contra-flow traffic management, consideration should be given to the provision of lane control signals and signs, and where this is not possible or appropriate, the opposing traffic flows should be separated by traffic delineators to Detail H or Detail K (narrow lanes). Where there is insufficient lateral clearance between opposing traffic flows to install Detail H or Detail K, the temporary central division should be delineated using a double white line road marking to diagram 1013.1A. These road markings must be removed and the lane markings reinstalled at completion of the works before reverting to uni-directional traffic flow (regulation 26).

For works associated on tunnels situated on single carriageway roads it is most likely that traffic will require to be diverted. However, where works can be limited to half carriageway width and traffic flows are low, shuttle working using temporary traffic signals to control traffic through the tunnel could be considered, refer to Section D5.10.

In addition to the portal and tunnel signs covered above, the traffic management designer must ensure that any tunnel prohibition notices (signs indicating users and/or materials banned by Order from a tunnel) are installed at appropriate locations in advance of a tunnel. Appropriate diversion signs should be provided to permit prohibited users to take an alternative route. 70