Traffic would be reduced on busy roads, the study says

Government plans would see satellite tracking charging drivers per mile on the busiest roads at the busiest times.

The University of Southampton-based commission says this would lead some motorists to detour along country lanes to avoid paying extra on major roads.

Its report warns this could increase traffic congestion in rural areas.

The report says the system would cut traffic congestion on busier roads by making journeys more predictable.

But instead of switching to public transport, drivers would try to drive early or late to avoid high charges, and also opt for car-sharing.

If the charges are added on top of the current car tax and fuel duty, it would amount to a few pounds extra a week for the average household.

But in London the increase could be as much as �20 per week.

'Big benefit'

Professor Stephen Glaister of Imperial College London, who has advised the government on road pricing, said it was important ministers made it clear where the extra money generated would be spent.

"If you spend the money by reducing fuel duty... it would make a big benefit in the rural areas," he told BBC Radio 4's Today programme.

"But if you keep the money to spend it on public transport or improving the road network, that's quite a different thing and that would look very different in cities and in rural areas."

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The department of transport has previously said that road charging would be fairer because those who travel greater distances would pay the most.

The government expects the first trial pay-as-you-go scheme to be operating by 2010.

Road pricing is already used in local and national schemes around the world including Germany, Australia and Asia.

In Switzerland, a heavy vehicle fee (HVF) has been levied since January 2001 and it takes into account the number of kilometres covered as well as the vehicle's weight and emissions.

It covers all roads and has been successful in its main aim of reducing lorry traffic across Switzerland.

The first city-wide charging for road use was introduced in Singapore in 1975. Later, electronic modernisation allowed prices to be varied aiming for maximum traffic flow at an optimal speed.

Singapore's Electronic Road Pricing (ERP) system uses a radio communication system to deduct charges from cash cards which are inserted in the In-vehicle Units (IUs) of vehicles before journeys.