The sensors will feed information about traffic levels to new regional traffic control centres, which will relay details to drivers on electronic noticeboards and dashboard display units in cars.
Private companies have been invited to submit proposals on how to run the system by charging motorists for information on alternative uncongested routes.
The announcement, by John Watts, the transport minister, was welcomed by motoring organisations but criticised by environmental groups, which said it would create greater congestion on minor roads.
Mr Watts admitted that the new measures would not mean an end to motorway jams.
"I don't believe we have found a panacea for congestion and I doubt whether we ever will," he said.
The new plan is to create three new regional traffic control centres which will work with the 32 existing police controls to give more detailed and quicker information on where tailbacks are and where they are likely to be in one to two hours.
One way that the improved information will be passed to drivers is through the use of the roadside electronic noticeboards, known as "variable message signs", now operating on motorways and trunk roads.
The road sensors are made of metal composite and are able to assess the amount of traffic on a road through alterations in the magnetic field. They will eventually be fitted throughout Britain's 6,500-mile network of motorways and trunk roads.
Mr Watts said that the scheme could be up and running within two to three years after the bidding process gets under way.
The Government believes that road traffic could double by 2025 but it is now committed to make as much use of the existing road network as possible and to persuading motorists to seek alternative forms of transport.
Drivers will be able to receive details of congestion on their in-car route-finding display units, which are becoming standard features in many new cars.
Yesterday's announcement was welcomed by Trafficmaster, a Milton Keynes company which has become the commercial world leader in what are known as "intelligent transport systems".
Trafficmaster has supplied 50,000 British motorists with route-finding equipment.
A visual screen-based unit which helps the driver to plan a route in advance costs pounds 150, and a verbal system, which gives information as the driver is going along, costs pounds 80.
Vauxhall has signed an agreement with the company to fit 100,000 cars with the new Trafficmaster Oracle system, which relays traffic details over the car stereo system using speech synthesis.
The AA said drivers would welcome more information but the project should not be used as an excuse to scale down existing road-building programmes.
Rebecca Rees, of the AA, said: "It is increasingly frustrating for millions of drivers every day. It is about time we had something like this. People don't know what the problems are, where they are or what alternative routes to take." The Government has admitted that by 2025, the number of cars on British roads will have doubled but that simply building more roads is not a realistic solution. Environmentalists said that rather than making things easier for drivers, the Government should be encouraging them to abandon their cars altogether.
Don Foster, the Liberal Democrat MP whose Road Traffic Reduction Bill will have its first reading in Parliament tomorrow, said the pounds 30m could have been better spent on encouraging people to use public transport.
"We are not trying to be anti-car but we want car use to be more efficient. The easiest way to do this is to reduce traffic," he said.
Lilli Matson, of the Council for the Protection of Rural England, said the plan could have the effect of masking the problem of traffic growth.
r Researchers are developing a sleep-detector in an attempt to curb road accidents caused by drivers nodding off at the wheel. A Rover 216 is being fitted with computer equipment to measure the effect of drowsiness on a driver.
The research at the University of the West of England, Bristol, has a two-pronged approach - on-board monitors will check a driver's control movements, such as steering, in the normal alert state and when fatigue sets in, and this information will be compared with "medilogs", recordings of brain, eye and muscle activity which focus on levels of drowsiness.
The researchers believe that computers currently involved in engine management could be adapted to include the logging of driver behaviour, so that warning signals could be given if driving control patterns indicated that a driver was in danger of falling asleep.Reuse content