Possible plan to put runway and taxiways on a bridge over M25 (not a tunnel) to save money

The Airports Commission (that cost almost £20 million) looked -in theory – at everything in great detail, and its (allegedly) incontrovertible recommendations have now been followed by government. It talked about the M25 needing to be tunnelled under the runway. It did not mention any sort of bridge.  But Heathrow was asked by government to cut the cost of its scheme (in order not to raise costs to passengers, to keep demand for flights high) so it came up recently with the idea of a bridge over the motorway. There is a bridge for one of the runways (+ taxiways) at Schiphol, so it is possible. However, there are enormous questions, not the least of which being that nobody has seen any details (cost, practicality, level of disruption, safety, terrorism danger etc) let alone been consulted. The section of motorway that might be bridged is the busiest on the M25, one of the busiest (it might be the busiest) in Europe, and the busiest in the UK. DfT figures show around 263,000 vehicles per day on the Junction 14-15 stretch in 2014. The runway would need to be raised about 8 metres in order to get over the motorway. Heathrow has only said it would spend a total of £1.1 billion for surface access infrastructure. The cost of tunnelling was estimated by the Airports Commission at £3.2 billion. Chris Grayling said absolutely nothing in his announcement, or in Parliament, about how much of the TfL estimate of £18 bn for surface access work the taxpayer would have to fund.


How do you build a runway over a motorway?

There’s an obstacle in the way of the proposed runway – the M25. An initial idea of constructing a road tunnel beneath the runway has been put aside. Building a “ramp” instead would be “a cheaper and quicker way of doing it”, said Transport Secretary Chris Grayling.

Heathrow is situated near the the M25’s busiest section, between junctions 14 and 15. Nearly 100 million vehicles flow through this stretch each year, according to Department for Transport figures.

Some on Twitter have joked that this ramp might resemble the front of some aircraft carriers that have a steep incline, known as a ski jump. “I can assure you it’s nothing like that,” says Chris Chalk, who’s on the transport expert panel for the Institution of Civil Engineers.

“In fact, you wouldn’t actually be able to see it with your eye. If you were on an aircraft you wouldn’t know about it.” [Note – this comment is only from the perspective of air passengers, not motorway users underneath.  AW note].

The gradient would be less than 1%, as required by the European Aviation Safety Agency. What impact would this have on a plane? “It doesn’t affect the performance of an aircraft or provide any problems whatsoever,” says Chalk.

“When an aircraft comes in to land, it’s coming in at a gradient of about 5% so less than 1% is a very small difference. In fact, it’s quite normal to have a runway with some gradient on.” [That is incorrect. Planes approach Heathrow, and almost all other airports, at 3 degrees. Link  Heathrow said:  “The international standard approach for most airports in the world is set at 3 degrees,” AW note].

Other UK airports that would have a greater gradient than that proposed at Heathrow include Bristol, Manchester and Birmingham.

Runway bridges have been built over busy roads including at Charles de Gaulle in Paris and Fort Lauderdale in the US state of Florida. Planes taxi along a bridge over a motorway at Leipzig-Halle airport in Germany and at Amsterdam’s Schiphol Airport.


Google map

Designers are required to allow a large amount of space either side of the runway in case there is an incident on the airfield. Strategically placed slats and the right lighting will be factors in preventing drivers from losing concentration due to planes overhead, explains Chalk, who works for the civil engineering firm Mott McDonald.

“You tend to have a number of visual buffers because you don’t want to distract the drivers. At that distance you won’t actually be seeing the aircraft that easily. It hasn’t created any issues elsewhere at other busy airports.”

So those thinking the boredom of being stuck in traffic on Britain’s busiest motorway might be relieved by the sight of a large aeroplane crossing the road will be disappointed.



The Airports Commission only ever mentioned tunnelling the M25

Its Final Report said:

“8.18 In addition, a range of works would be needed on the road network to accommodate the expanded airfield site including, for both schemes, the tunnelling of a section of the M25 to the west of the airport.”



PLANE CRAZY  – Heathrow Airport’s third runway could see jumbo jets taking off from a ‘ramp’ over the M25

The Government’s decision to choose Heathrow for expansion has caused deep rifts in the Tory Party

Times said  27.10.2016 : 

Heathrow confirmed yesterday that it would sign initial contracts with engineers, architects and planning consultants “within days” to start the third runway after being given the government’s approval, insisting that 95 per cent of spending would go to British suppliers.  Link 

BALPA say the slope of the runway – even 1 degree, affects how planes land and take off


The British Airline Pilots Association (Balpa) said that other runways around the world operated on gradients, usually as a result of being built on sloping ground. However, it said there was a chance that an aircraft’s autolanding system — usually used to bring the plane down in fog — may not work on some slopes.

At least one other runway — at Fort Lauderdale in Florida — is built on a man-made slope. It is almost 16m higher at one end to accommodate a goods railway underneath.

Stephen Landells, Balpa’s flight safety specialist, said: “Putting a slope on a runway isn’t a problem. But any change to the runway has a significant impact on the performance of the aircraft. So before take-off or landing, one of the things you have to consider is the slope of the runway.

“On take-off, you will work out the power you need. If you have got quite a steep slope it is going to take longer to accelerate and more power. On landing, it has an effect if you land downhill because it is going to increase your landing roll.”

He added that there was a risk the autolanding feature may not work.

“The use of autoland is also limited,” he said. “The limit on most aircraft will be around two degrees, and if it is greater than a two degree slope you can’t use the autoland. Not having autoland at Heathrow would not be a good situation to be in because any fog would cause problems. You can’t just close a major international airport.”

See full article in the Times at



Putting Heathrow runway over M25 will be ‘cheaper and quicker’ Transport Secretary Chris Grayling says

The plan is for the runway to span the 12-lane highway

By Jon Stone, Political Correspondent (Independent)

The Transport Secretary has defended the Government’s plan for Heathrow’s new runway to span the M25 using a ramp, arguing that the solution will be “cheaper and quicker” than alternatives.

Chris Grayling said that the new runway had to be “affordable for passengers” and that the ramp over the 12-lane motorway would only be a “gentle slope”.

Ministers yesterday gave their backing for the new runway, the design of which suggests using an 8m ramp to span Britain’s widest motorway at its widest point.

Mr Grayling said the proposal was “sensible”, seeking to assuage safety and security concerns of having sensitive infrastructure just metres in the air over a busy road.

“We’ve been very clear not just to [Heathrow] but to the other promoters of the schemes is that what they do has to be affordable for passengers as well. It’s not simply about landing extra costs on the shoulders of passengers,” Mr Grayling told BBC Radio 4’s Today programme

“One of the things that Heathrow has been looking at is doing what many airports have done around the world and building their runway over the top of the road rather than tunnelling the road underneath it.

“It’s a cheaper and quicker way of doing it and I’m of course very concerned to make sure that whilst this runway is built it doesn’t cause massive disruption on the M25.

“I think this is a sensible way, it’s a gentle slope. It’s a hill, a very gentle hill upwards that the planes would take off rather than a flat service and it’s what happens at very many other airports around the world.”

Other proposals considered include putting the M25 into a tunnel, building the runway at a different alignment, or building it elsewhere.

MPs will vote on the new runway in 2017-18 following a public consultation.

The third runway is expected to be operational not before 2025, with construction slated for 2020-2021, barring any further roadblocks.




Heathrow conceded on Tuesday night that it may have to re-examine its plans for an extension under the M25, possibly replacing the tunnel with an elevated bridge, after it emerged that Highways England, the body in charge of Britain’s major roads, considered the scheme a major risk.

Highways England warned there was a “significant risk of cost overruns” in the M25 tunnel scheme, the bill for which it estimated would be between £476m and £1.1bn. Correspondence released by the Department for Transport showed that the roads authority described the scheme as “high risk”, warning of a “a substantial risk of excessive customer frustration about what might be prolonged period of disruption”.