LONDON - British motorists could be taxed according to the distance they drive as judged by a satellite, under radical plans to ease the country's congestion problems, a government transport think tank said Sunday.

Motorists could face monthly bills calculated by in-car satellite navigation systems as part of a plan to reduce traffic on busy roads, the Commission for Integrated Transport (CFIT) said in a report that will be put to ministers Monday.

Under the proposals, Global Positioning System (GPS) satellites would track vehicles via electronic "black boxes" fixed to car dashboards, AFP reported.

Prices would be set according to the level of congestion, and could reach as high as 45 pence (50 U.S. cents, 57 euro cents) per mile (27 pence, 30 U.S. cents, 34 euro cents per kilometer) in central London.

The average weekday charge would be 3.5 pence per mile on motorways and 4.3 pence a mile on other roads, according to the report, although travel would be free off peak and on quiet roads.

"Roads are the only public utility that is free at the point of use," said CFIT Chairman David Begg.

"As a result, everyone wants to use the most popular roads at the same time. Result: gridlock. There has to be a better way, the public debate must start now."

The government's transport department said the recommendations in the report would have to be considered before any action was taken.

Opposition Conservative Party transport spokeswoman Theresa may voiced her disapproval at the proposals and said she didn't think the charges would deter drivers.

"Yet again it is an attempt at a sort of stealth tax, trying to price the motorist off the road, and I don't think that actually works," she told BBC television.