Quote Originally Posted by The Bloop View Post
Driving at 70 means you arrive at the congestion sooner spurting out your pollution for longer in stationary traffic. Youre also using more fuel at 70. Driving at 50 keeps you moving for a longer time creating less pollution and uses less fuel.
It doesn't though. Traffic approaching the 50mph zone at 70mph has to slowdown quickly, thereby causing more congestion behind. The congestion isn't there until the 50mph zone starts. Within the congestion, traffic is driving at between 5-20mph, thereby causing more pollution. Apart from the 50mph zones, the main other reason there is congestion on the M4 in both directions is the existence of the tunnels at Brynglas which causes queues in both directions for miles at peak times. The is more congestion on the M4 now than before 50mph zones were introduced.