Special signs will tell...

Special signs will tell motorists to treat it as an additional lane in heavy traffic. A Highways Agency spokesman said: "If the flow is congested, overhead signs will impose 50mph limits and open the hard shoulder."

State-of-the-art gantries are to go up every 500 metres between junctions 3a and 7 of the M42 in the West Midlands. But what if a breakdown or crash blocks the way? "We can change the signs to clear the hard shoulder and let emergency vehicles through," the official added.

Yet the system is smarter than that; if CCTV shows the outside lane would be a better bet for 999 vehicles, signs tell drivers to get out of that instead. In addition, hi-tech "emergency refuge lay-bys" will allow cars in trouble to pull out of the way during hard shoulder running. Pressure sensors beneath the surface will trigger cameras to monitor the situation. The AA"s Paul Watters welcomed the trials, due in 2006. "If traffic keeps moving, there"s less chance of shunt accidents," he said.

See page 20 of this week"s issue: Did you know?