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LONDON - Spies in the sky may track motorists in Britain within a decade if the government goes ahead with controversial plans to introduce road user charging schemes, scientists said today.

The plans were unveiled in a report on future transport policy in November as a way of cutting congestion and prompted 1.8 million people to sign an electronic protest petition.

Monitoring would be via a combination of static cameras to capture license plate details, electronic tags in vehicles that would be read by roadside monitoring stations and global positioning system satellites to read on-board transponders.

"You will need 10 years at a minimum for a national rollout," Phil Blyth, professor of Intelligent Transport Systems at Newcastle University, told reporters. "I do not see many other options available to us to manage our transport system."

Blythe, head of a panel of transport experts from the Institution of Engineering and Technology, said the technology was already available and had been tried and tested in various countries including Australia and Brazil.

The London congestion charge zone uses static cameras and will bring in electronic tags from 2010. Cities such as Singapore have been operating electronic tagging for years and Stockholm's pilot scheme becomes permanent in July.

Extension of existing GPS SatNav technology would be a simple feat, panel members told a news conference.

Panel member Bill Gillan from the Transport Research Laboratory said he believed that eventually satellite tracking would supersede the other technologies.

National coverage

Not only could it allow for variable rates at different times of the day to smooth traffic flows, but it could also track distance and provide cost-effective national coverage.

However, cost was the key. "How do you encourage people to fit an on-board unit to their car?

"You have to juggle the cost, the charges and the penalties and offer some carrots as well as sticks," he said. Simply making manufacturers fit tracking systems to all new cars would not be sufficient to guarantee rapid coverage, he said.

Panel member and transport consultant Jack Opiola said the thorny issue of personal data privacy could easily be dealt with by appropriate laws.

There are 30 million vehicles on the roads of Britain, a figure forecast to surge by one-third within 15 years, increasing journey times that industry complains are hurting competitivity.

Blythe said the government had to explain clearly to people what was at stake in terms of personal benefits from faster journeys and global gains from reduced greenhouse gas emissions due to fewer traffic jams.