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THE M42 IN THE West Midlands is to become the
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second motorway in the country using variable speed limits to manage congestion. The Highways Agency says from December the rush-hour limits will be introduced between Junctions 3A and 7.
HA traffic management specialist Simon Kirby says advisory limits have been successfully operating there over the past nine months: "I don't hear much about congestion on the M42 on the local traffic news unless there's been a specific incident. Before that there were regular hold-ups." Variable speed limits are already used on the M25 to discourage drivers from frequently switching lanes because one line of traffic appears to be going faster than another. "Cars brake because someone pulls in front, creating a ripple effect all the way down the motorway," says Kirby. "There's a marked change in driver behaviour [with variable limits]. There's more space between cars, the traffic flow is smoother and you don't have that stop-start situation."
Provided mandatory speed limits prove successful, the agency will open up the M42 hard shoulder as a fourth traffic lane during the rush hour.