Heathrow Airport has revealed plans for a series of viaducts to cross the M25, one of which would be the third runway.
The widest of three parallel viaducts bridging the motorway would act as the runway, while two narrower viaducts would function as taxiways for planes. Expansion programme director Phil Wilbraham shared the plans at an engineering conference, according to the Sunday Times.
The news comes after Wilbraham told delegates at New Civil Engineer’s Airports 2017 conference last month that the 3,500m third runway would likely “extend over the top” of the M25, which would be moved to the west and lowered. He said ground conditions and rivers close to the runway path would create extra challenges for engineers designing the £17bn runway, which could be built using precast concrete.
Building viaducts over the motorway is believed to be cheaper than alternatives considered by the design team, including rerouting the M25 through a tunnel.
Willie Walsh, chief executive of International Airlines Group (IAG), has called for a shorter runway to be considered to save commuters from disruption by not bridging the M25. However, the Airports Commission dismissed proposals for a shorter runway as it would cause higher levels of noise pollution.
“Like all major infrastructure projects, we have to balance several factors in our delivery plans: risk, construct ability, passenger experience, quality, affordability, environmental impacts and time,” said a spokesperson for Heathrow.