Originally Posted by
SirHumphreyNorth
Does doubling the size of the M4 bring air quality down?
Originally Posted by
Prophead
LHR will be part of a new and world class transport system that combines HS2, Crossrail, LHR and an upgraded motorway network.
Leaving the rail developments aside, I'm not aware of any plans for more tarmac on the M4, other than the currently proposed scheme (whether R3 goes ahead or not) to turn it into a "smart" motorway à la M42/M3 by utilising the hard shoulder.
Whether the M25 tunnel plan represents an "upgrade" is a moot point. We're told it will gain a lane in each direction, but I wouldn't be surprised if that gets trimmed back once the infrastructure costs start to be firmed up.