The Government has approved an £860m scheme to remove the hard shoulder on the M4 and turn it into a running lane in Berkshire.
The decision was revealed by campaigners tonight following a letter sent to them by the Department for Transport.
It will be the biggest and most expensive road scheme the region has seen.
The entire section between Hayes, near Heathrow and junction 12 at Theale will be converted - the longest section of so-called Smart Motorway in the country.
The Government say it will reduce congestion. But campaigners have expressed anger.