Transport for London (TfL) is extending the trial of car-tracking tags for its Congestion Charge road system.
The wireless car-tracking system is a possible parallel system to the current automatic number plate recognition CCTV enforcement system.
Smart tags can be fitted to a vehicle to alert roadside beacons when the car drives past.
TfL is investigating whether to use pre-pay tags, which can be spent as the vehicle enters the congestion charge zone.
TfL started a very small-scale trial earlier this year, but is now setting up a car-tracking tag system in the Southwark area of London, involving around 500 volunteer drivers and 20 tracking beacons.