 The decision to put part of the road in a tunnel pushed the cost of the project to £371 million, with the underground section costing £155,000 per metre (£142,000 per yard) making that section of road the second most expensive road in the UK per unit distance, after the Limehouse Link tunnel.The Hindhead tunnel runs through a sequence of fine grained strata of the Lower Greensand Group, which were laid over Weald Clay during the Lower Cretaceous period (70140 million years ago) on the margins of the subsiding Weald Basin.The Greensand group consists of the Hythe Beds, which overlay a layer of Atherfield Clay.