Mott MacDonald-designed A3 Hindhead road scheme opens to the public

1 August 2011

The A3 Hindhead road scheme, which completes the dual carriageway link between London and Portsmouth, officially opened on 27 July. Mott MacDonald, working for Balfour Beatty, was responsible for design and construction supervision of the 6.5km dual carriageway including a 1.8km twin bore tunnel.

The project alleviates a major source of congestion around the A3/A287 traffic signal controlled crossroad and improve road safety through Hindhead and around the Devil's Punch Bowl and Hindhead Common.

Areas surrounding the A3 at Hindhead are of Special Protection Area status and include part of the Surrey Hills Area of Outstanding Beauty and National Trust owned Sites of Specific Scientific Interest. Consequently a major consideration in the design was assessing and mitigating potential environmental impacts associated with the road improvements.

Giles Hewson, Mott MacDonald's environmental coordinator for the project said: "The project has involved extensive landscaping including replanting of local woodland, creation of new heathland areas, a fully-planted green footbridge and vegetated slope finishes. In addition, the old A3, within the natural beauty spot of the Devil's Punch Bowl, will be removed and the area restored to heathland."

The impact of the road has been reduced by constructing a tunnel beneath Hindhead Common, and much of the new A3 has been placed in steepened cuttings and embankments to reduce its footprint leaving more of the neighbouring woodland intact.

At the south of the tunnelled section a major cutting has been created while to the north an embankment has been built. The elevations of the road were designed to balance the quantities of cut and fill, ensuring that no materials needed to be removed from site as waste and limiting the quantities of imported material. Reusing such materials required extensive onsite testing and assessment before they could be included. Mott MacDonald carried out extensive research into the steep reinforced cutting slopes to ensure stability and maximise vegetation growth opportunity.

The Mott MacDonald designed tunnel has twin bores, each housing two lanes. To support the tunnel walls and face, a lining of sprayed concrete was applied. Innovations include use of a sprayed waterproof membrane and improvements to the sprayed concrete mix. Using laser surveying and robotic machinery enabled tight quality control improving structural performance. This permitted material and time and environmental savings, as the primary lining of the tunnel has been regarded as part of the permanent works.

Fully compliant with European regulations for road tunnels it incorporates many features which enhance road user safety. These include:

-Linear heat detectors which will inform the tunnel control of any fire and its location
-Radar coverage to detect vehicle incidents and other hazards in the tunnels
Intelligent lighting and signing in the tunnels, including the use of LED cat's eyes to guide motorists
-Comprehensive fire fighting systems, and resilient systems to support emergency evacuation in the event of a fire.

Commenting on the safety features of the tunnel Simon Stephenson, Mott MacDonald's resident site engineer said: "The tunnel boasts state-of-the-art safety and communications systems. In addition, the tunnels are connected by cross passages at 100m intervals to allow emergency escape."

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