The Government has backed the construction of a third runway at Heathrow despite widespread objections on environmental grounds. Zac Goldsmith, who stood for the job of London Mayor, has resigned as an MP as a result. Both he and elected Mayor Sadiq Khan opposed that development.
It will bring major challenges to the road network because the new runway will have to run over the M25. So that will likely have to be moved into a tunnel. In addition the western side of the M25 is one of the most congested parts of the UK road network already and the extra traffic generated by Heathrow expansion will make that even worse. So widening of both the M25 and M4 is probably required. The costs of those improvement could be over £3 billion and it could take over 6 years to implement with no doubt a lot of traffic disruption while it is being built.
In addition the extra aircraft movements and more traffic will have negative environmental impacts in both air pollution and noise.
Comment: this is surely one of the worse decisions ever made by a UK Government. There were a number of better alternatives for airport expansion, including the encouragement of the use of other regional airports. Why does the whole country find it necessary to travel through Heathrow when smaller airports are altogether easier to use?