Transport for London (TfL) has ruled out the use of satellite tracking technology in its congestion charging scheme because it is insufficiently mature.

The second stage congestion charging technology trials concluded that tag and beacon – which involves vehicles being fitted with credit card-sized tags detected by a beacon using radio frequency identification (RFID) – is instead a far more robust option for pay-as-you-drive charging (Computing, 19 October).

The tag-and-beacon technology is widely used on major motorways in other countries, including France and Italy. The report into the London trials says tag and beacon has a successful detection rate of 99.95 per cent and works well even on smaller roads in urban areas.

Number plate recognition technology used at the moment, however, will still be required for enforcement of users that do not join the tag scheme.

TfL installed tag-and-beacon technology in 10 test vehicles and issued PDAs to create multiple streams of data. It was overlaid onto the original source of data, determined by sending the cars along specific routes to identify any missed vehicle passes.

The data was put though a series of matching algorithms to test overlap between the tag-and-beacon technology and number plate recognition technology.

The trials, intended to move from a proof of concept to feasibility of technologies, conclude that it will be some years before satellite tracking will become a viable option.

TfL global positioning systems architect Nick Williams says back-office applications such as map matching are not sufficiently advanced.

‘The most important aspect of the trials was the end-to-end processing and not just the accuracy of the on-board unit,’ he said.

‘The overall performance was significantly better than expected in some cases, but nowhere near where we need to be.’

Williams says the average location error has dropped from 9.7 metres 18 months ago to 6.7 metres during the recent trials. The best performing system also had billing errors of less than one per cent.

Gartner analyst Mike Williams says satellite tracking technology continues to evolve.

‘There is a greater chance for positioning error in city centres because the satellites can be obscured,’ he said.

‘But the launch of the European Galileo satellite navigation system is likely to enhance vehicle positioning when it launches in three years’ time.’

AA Motoring Trust’s head of road and transport policy Paul Watters says any future systems, whether satellite tracking or tag and beacon, must be reliable.

‘The system was strained when it launched and the risk of errors during introduction of a new system is a big concern,’ Watters said.

‘But tag-and-beacon tracking could enable the introduction of monthly accounts or allow the charge to be paid using an Oyster card to create a truly integrated system,’ he added.

Road charging... in 30 seconds

z Transport for London’s (TfL’s) congestion charging technology trials started in 2003 to investigate how new technologies could provide additional flexibility in payment. Stage two aimed to move from a proof-of-concept to technical feasibility.

z It examined a range of technologies, including tag and beacon detection, satellite tracking, distance-based charging options and valued-added services such as sending alerts automatically to drivers’ mobile phones.

z TfL has communicated its results to the Department for Transport, which is preparing its own trials of satellite tracking for road user charging. It is working with local authorities to develop a number of regional pilots.

z Norwich Union has officially lau nched its own pay-as-you-drive scheme for drivers to manage insurance costs. A black box is installed in vehicles to record the distance travelled and the monthly bill is calculated from the data gathered.

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Further reading

TfL says no to satellite tracking

London tests satellite tracking

London looks at car tracking options