Tens of millions of pounds is being spent giving the road tunnels into Heathrow a makeover to improve safety and allow a new generation of heavier planes to travel on the runway which goes over them.
The tunnels off the M4 were built in the 1950s and are used by 55,000 vehicles a day.
Now the two 630m-long access routes are being refurbished in overnight works to allow the airport to operate as normal during the day.
New fire systems are being installed and they're being made stronger to cope with a new generation of larger planes like the A380.
Residents around Heathrow are furious over today's announcement that the airport is the preferred option for a new runway. Interviewees: Helen Hansen-Hjul and Murray Barter.
Boris Johnson has told ITV News that the Airport Commission's proposals for a third runway at Heathrow will lead to a massive increase in noise and air pollution over London and suggested little has changed since the West London airport's first plans for redevelopment three years ago.
The Mayor of London seemed wary that the planned expansion would lead to the erosion of a night flight ban and eventually a fourth runway, which Mr Johnson said would be a "real disaster".
Conservative MP Zac Goldsmith, who is seeking nomination as the party's candidate for London mayor and has been a vocal opponent of a third runway, said:
It's not going to happen. I don't think anyone believes Heathrow expansion is possible or deliverable politically. There are conditions in this report on air quality and noise pollution that are irreconcilable with Heathrow expansion.
Mr Goldsmith said he would honour his pledge to stand down as an MP and force a by-election in his Richmond Park constituency if a Conservative government gives the green light to the third runway option.
Labour MP John McDonnell, whose Hayes and Harlington constituency includes Heathrow, said:
My community has been absolutely betrayed by David Cameron who said 'No ifs, no buts, no third runway'.
We will fight with every mechanism available, including political lobbying, legal action and where necessary direct action to save our homes and community.
The Davies proposals will result in 4,000 homes being demolished or rendered unlivable by air and noise pollution, including the demolition of schools, community centres and places of worship.
The Davies proposal for a third runway at Heathrow will provoke the biggest environmental campaign the UK and Europe has seen. The fight goes on.
Here are the key statistics in the Airport Commission's proposal for a new runway at Heathrow.Read the full story ›
Boris Johnson has said that he is "disappointed" with the Airport Commission's recommendations and predicted that a third runway at Heathrow would never be built.
In a tweet the Mayor of London said: "Davies commission pro Heathrow is disappointing - compounds not solves issue - destined for vertical filing as 3rd r/way will never be built."
Davies commission pro Heathrow is disappointing - compounds not solves issue - destined for vertical filing as 3rd r/way will never be built