By the end of the year, the M8 between Edinburgh and Glasgow will become the country's first road to show actual driving times to key junctions.

Such signs will also be used to display more "green" motoring messages, to help cut fuel use and emissions.

The roadside signs will display the distance and current journey time to junctions ahead, using a network of cameras which track vehicle number plates.

The technology, already in use in England, will later be extended to other busy motorways, such as the M90 approaching the Forth Road Bridge.

The M80 between Glasgow and Stirling, M9 between Edinburgh and Stirling, and the M74 between Glasgow and the Border will also be covered.

The Scottish Government's Transport Scotland agency, which is responsible for motorways and other trunk roads, said the information would provide a key aid for drivers.

Jim Barton, the agency's director of trunk roads management, said: "The aim is to provide reliable and robust information. It's not the shortness of the journey that is important to people, but the reliability – knowing how long it's going to take."

Mr Barton said more environmental messages would feature on the electronic signs, following on from the current "Slow down, save fuel".

Mr Barton said: "The environmental message is something which we will begin to promote, which could include encouraging motorists to drive at a constant speed, and to think about alternative travel modes, such as bus and train. However, the focus is very much on carrot, not stick."

He said a planned "Don't Panic Buy" message during the tanker drivers' strike in June had been withdrawn for fear of inflaming the dispute.

The Traffic Scotland website includes a "carbon calculator" which compares the emissions of cars, trains and buses for the same journey. A cost comparison between the modes of transport is also planned.

The Association of British Drivers, a motoring lobby group, backed improved information on journey times but said that environmental messages would prove to be counter-productive.

Bruce Young, its Lothian and Borders co-ordinator, said: "I have been very impressed by the sign on the M8 westbound into Glasgow (at Easterhouse] which accurately predicts the journey time to Charing Cross and other landmarks. These will be very useful in helping drivers to judge their arrival time.

"However, 'green' messages are less useful. They are often painfully obvious and more likely to distract and even irritate drivers.

"Instead, sensible road safety messages such as the two- second rule (leave two seconds between your car and the one in front] and seatbelt wear would be useful."

Cameras to put drivers in picture

A NETWORK of 400 cameras will supply the journey-time information by recording how fast vehicles travel between two designated points on the motorway network.

These cameras will use automatic number-plate recognition technology to track movement and then calculate average journey times, which are then displayed on electronic signs.

The equipment is similar to that used by the police, who operate a separate network of cameras sited across the roads network. They are also fitted to police cars, allowing

them to track criminals. It can also check vehicles at a rate of nearly one a second to ascertain whether they are insured and have road tax.