Transport for London (TfL) is investigating in-car satellite tracking technology for the capital's congestion charge zone.

The organisation says that it has no definite plans, but is inviting suppliers to demonstrate what technology is available and its accuracy, with a view to establishing a more flexible road pricing system.

'TfL is interested in reviewing systems that could accurately distinguish between route, zone or other units of charging,' say TfL documents.

'We are reviewing various ways of representing road charging elements electronically, so that positional data can be used to determine if a charge is due.'
Possibilities include on-board systems that trigger a fee as the car passes an electronic 'fence', or the development of charges on the basis of distance or only at a specific time of day.

'A charging unit could be a road or route to which TfL may wish to apply a charge; for example, a strategic route extending a few kilometres,' say the TfL documents.
An on-board unit would need to be able to distinguish between specific priced roads, a general charge zone and uncosted roads, as well as calculating fees, storing and dispatching data back to central systems.

Global positioning systems were first considered by TfL in 2003, but the technology was deemed insufficiently advanced.

'We want to see if there are more mature products, and to look at how accurate these systems would be,' said a spokesman for TfL.

'This is not a policy change or a plan to change the structure or the way that the congestion charge works.'

TfL is to begin trials of tag and beacon technology this month. If successful, the technology could supplement the existing camera-based number plate recognition system when the current supplier contract runs out in 2009 (Computing, 28 July).