Description of Works
CONWAY AECOM, FM Conway’s joint venture with AECOM, has delivered a major refurbishment of the lighting in the A40 Hanger Lane Tunnel – one of London’s busiest carriageways.
As the London Highways Alliance Contract (LoHAC) delivery partner for Transport for London in the North West of London, CONWAY AECOM carried out the work as part of TfL’s tunnel refurbishment and upgrade programme.
The London Highway Alliance (LoHAC) is a term contract covering the complete spectrum of highway services from the routine maintenance of assets through to the delivery of major capital schemes. Our FM Conway lighting team were engaged to replace the existing lighting systems in the Hangar Lane Tunnels.
The Hanger Lane tunnels are 240m long bore tunnels encompassing two traffic lanes per bore. The average width of tunnels is 7.6m with height generally limited to 4.9m. The tunnels were subject to a programme of modernisations and refurbishments, which included the replacement of the existing lighting systems with dimmable LED’s as well as the installation of a number of safety enhancements installed by others but managed by FM Conway.
The works were phased with advanced temporary works to the LV switch room, including a temporary control panel being accepted before the disconnection and removal of the existing lighting boards. This included disconnection of incoming supplies and redundant field cabling. The new lighting system incorporated an eMaster control system.
Logistically, the fixtures were transported to the works areas using MEWPs. These also provided working platforms for the installation works. The trays were unloaded from the MEWP at verge level prior to installation and fixing. Bespoke stainless brackets were wall fixed using M10x75 torque controlled bonded anchors. Similarly, the Dali boxes were fixed off the MEWP platform providing connection between the LED units.
Tom Chipperfield - Contracts Manager at FM ConwayOur overriding objective throughout the project was to minimise disruption for tunnel users by making the best use of the time we had on site.
An intrusive asbestos survey carried out at the start of the upgrade works to review the project risks revealed the works would be far more complex than expected. This was due to the joints between the tunnel’s precast soffits having been originally sealed with a caulking material which contained some asbestos. Due to years of water ingress and contamination, the caulking material had begun to decay.
To combat this, the team utilised an asbestos encapsulation system designed by asbestos and environmental services specialist Forest Environmental. A curing membrane from structural repair specialist Flexcrete was applied to seal the substrate and consolidate any loose material. Then a water-based, non-hazardous cementitious coating was then applied in two coats to lock in any remaining asbestos fibres and provide a permanent, waterproof seal over the surface of the joints.
A lighting condition survey confirmed the installed lighting in the tunnel was below acceptable standards. A temporary lighting solution and speed restrictions were implemented for road user safety in November 2014 while a detailed lighting design featuring new LED lighting was developed.
LED luminaires are usually fixed directly into the tunnel soffits. However, in this case drilling into the soffit to install the luminaires would undermine the integrity of the encapsulation system. To solve this, the CONWAY AECOM team designed a bespoke stainless-steel bracket system which the luminaires and supporting cabling infrastructure could be mounted onto and fixed to the wall.
The works were delivered to a 16-week programme, with all traffic management being paced and removed on a nightly basis. All plant and materials had to be cleared from and returned to the site within each shift.
Tom Chipperfield, Contracts Manager at FM Conway, explains the challenges the team faced:
“Our overriding objective throughout the project was to minimise disruption for tunnel users by making the best use of the time we had on site. Working closely with TfL and their LTRA Cs Contractors (CUBIC), we enabled other planned works to be undertaken at the same time as the lighting upgrade, including the renewal of the PA, radio and CCTV systems. The lighting upgrade project was completed safely in just 16 weeks.”
The key objective was to complete all works by a prescribed date to avoid delays to subsequent key projects on the route. Route closures and traffic management systems and times were agreed in advance with Police and local authorities.
Furthermore, cost and time savings were achieved for the client through encouraging multiple occupancy of the traffic management systems. This was achieved through FM Conway’s management of the other specialist supplier that was engaged to install the supplementary CCTV and PA systems.
Steve Ryan, TfL’s tunnels technical manager, said:
“CONWAY AECOM was commissioned to replace the aging and dilapidated tunnel lighting with a modern, energy efficient LED system. The age and nature of the Hanger Lane Tunnel provided a challenge for their design team, which was solved collaboratively.”