The congestion toll system in Stockholm was trialed in the first half of 2006 and was implemented full-scale in 2007. The system has been developed in cooperation with the Swedish Road Administration, the City of Stockholm and IBM.

The technology is based on a system which registers passing vehicles during regular traffic flow, not requiring that they slow down or halt. Registration is performed using a laser and camera connected to the system in order to identify and bill vehicles. The technology used during the trial in 2006 is described below. When the system was fully implemented in 2007, the transponder in the second step was eliminated and the license plate was photographed instead.

1. The vehicle breaks the first laser beam which activates the transmitter/receiver used in the second step.

2. The transmitter/receiver captures signals from the vehicle’s transponder and registers the time, date and toll rate.

3. At the same time, the vehicle’s front license plate is photographed.

4. The vehicle breaks the second laser beam and activates the second camera used in step 5.

5. The second camera photographs the rear license plate – all this without requiring the vehicle to reduce speed.

6. The toll is either automatically deducted from the driver’s account or can be paid via the Internet, at a bank or a 7-Eleven or Pressbyrån convenience store.

(Source: www.ibm.com/podcasts/howitworks/040207/)