MOTORISTS will be able to drive on motorway hard shoulders at busy times as a cheap alternative to road widening.

Motoring groups said that the idea would reduce delays for millions but gave warning that emergency services would take longer to reach road accidents because there would be no spare lane.

The measure will be introduced on many of Britain’s congested motorways, increasing capacity by a third at a fraction of the cost of building an extra lane, if a pilot scheme proves successful.

Hard shoulders can be converted for use by traffic in only two years, compared with up to ten years to plan and construct additional lanes.

Drivers who break down on the motorway will be able to pull into new lay-bys, known as emergency refuges, which have been built at 500-metre intervals.

Access to the hard shoulder will be controlled via a series of gantries across the motorway. Sensors under the road surface will detect when congestion is building up and send a message to the agency’s control centre.

Digital screens on the gantries will inform drivers that they can use the hard shoulder. The gantries will display a red cross over the hard shoulder when it is closed and a round speed limit sign when it is open.

The limit for all lanes will be reduced to a maximum of 50mph when the hard shoulder is in use. Reducing the limit in congested conditions has been shown on the M25 to improve average journey times by deterring lane hopping.

The control centre will use a network of CCTV cameras to spot when a vehicle breaks down and cannot reach a refuge. The Highways Agency said that signs on the gantries would be changed in seconds, telling drivers to leave the hard shoulder and warning of a hazard ahead.

From next month drivers will be directed to use the hard shoulder in a pilot scheme on an 11-mile (17km) stretch of the M42 southeast of Birmingham. The Highways Agency is also considering extending the idea to most of the rest of the motorway box around the city, including stretches of the M5 and M6.

The M42 scheme cost £100 million, compared with the £500 million it would have cost to widen the motorway.

An agency spokesman said: “We get a big increase in capacity for a fifth of the cost and there is no environmental penalty because we do not have to extend the land boundaries of the motorway. It’s all about making best use of the available space.”

But the AA Motoring Trust said that the scheme may confuse drivers. Paul Watters, the trust’s head of roads policy, said: “We are concerned that drivers will develop the habit of using the hard shoulder and fail to notice when it is closed. They may then crash into a vehicle which has been unable to reach a refuge.”

He said the agency had added to the confusion by being inconsistent in its methods of squeezing more capacity from motorways. On the M1 and M62 near Leeds, the agency is creating an extra lane by narrowing the existing lanes and using the verge as a hard shoulder. On the M25, it is widening the carriageway to create a permanent fourth lane.

“We welcome the extra capacity in each case but it would be safer to have a consistent approach,” said Mr Watters. But he accepted that it would be safer for AA patrolmen to carry out repairs in refuges rather than on the hard shoulder.

The agency said that the Netherlands had been allowing traffic to use some hard shoulders for a decade and had recorded a decline in crashes.

The Freight Transport Association said hard shoulders should be used on all the most congested motorways, especially the M1, M6, M5, M25 and M62. A spokesman said: “We need action right now to relieve worsening congestion on those roads and the hard shoulder offers a relatively cheap and simple solution.”

Traffic on motorways and inter-urban A roads in England is forecast to increase by at least 40 per cent by 2015, according to the Department for Transport.

The Highways Agency said it would not be possible to convert the hard shoulder on motorways built on stilts because creating refuges would be prohibitively expensive. But motorways where the hard shoulder narrowed at bridges could gain an extra lane by reducing the width of the central reservation.

Motorway traffic has increased by 37 per cent in the past ten years, but the network has grown by only 0.5 per cent, or 175 miles. Motorways carry a fifth of all traffic but represent less than 1 per cent of the total length of all roads.

They are the country’s safest roads, with a death rate of 0.1 per million km (625,000 miles) driven, compared with 0.7 on rural roads. There were 164 deaths on motorways in 2004.

Other schemes for reducing congestion include installing traffic lights on entry slip roads on the M6, M60, M62 and M25. Vehicles enter the motorway only when there is a gap in the traffic.

The agency will also give a trial to American-style car sharing lanes on part of the M62 and M606 in West Yorkshire from next year, and on the M1 between St Albans and Luton from 2008. Only drivers carrying at least one passenger will be allowed to use the lanes