Hindhead Tunnel on the A3 is the longest road tunnel in the UK not passing beneath a river. At 1,830 metres, it forms part of the 6.5 km Hindhead by-pass.
The A3 links Portsmouth and London and by 2000 was almost entirely dual carriageway. The exception - and significant bottleneck - was the single carriageway section through Hindhead in Surrey. A few years earlier, a surface by-pass would have been the likely solution but environmental concerns around the impact on the important natural habitats including the Devil’s Punch Bowl meant that a tunnel solution was chosen.
Excavation of the tunnel started in February 2008 and used the New Austrian Tunnelling Method (NATM) where excavation uses a mechanical digger and the exposed rock is immediately sprayed with quick-setting concrete. Geologically, the tunnel passes through lower greensand strata. The initial excavation was of just the upper half of the tunnel until breakthrough was achieved in February 2009. Refuges and cross tunnels for safety reasons were bored every 100 metres.
Sub Brit was lucky to have a tour of the tunnel in 2010 when the physical excavation was complete and fitting out work was underway. A larger attendance was possible on 14 May 2011 when 7,000 members of the public were allowed to walk through the tunnel. Formal opening took place later the same year, on 29 July. After the opening of the tunnel, part of the old A3 was torn up and returned to nature.