Road user charging

How road user charging works

There are essentially three types of scheme design for road user charging systems:

• An area, cordon or zonal charge e.g. London, Durham, Singapore, Oslo, Trondheim, Rome, Bergen, Stockholm.
• A fixed length link e.g. M6 Toll, Melbourne, Santiago, French Autoroutes, Toronto, San Diego.
• A distance based charge e.g. Switzerland, Austria, Germany.

There are essentially three basic mechanisms by which these charging schemes can operate:

• Physical systems - M6 Toll, French Autoroutes.
• Permit based systems e.g. London, Rome, Austria, Hungary, Singapore's early scheme.
• Electronic systems - using either microwave or global positioning satellite (GPS) technology - Japan, Germany, Trondheim, Melbourne, Oslo, Port Authority of New York & New Jersey, Austria, Rome, San Diego, Santiago, Stockholm, French AutoroutesSwitzerland, Toronto.

These three mechanisms are perfectly capable of operating together within an overall system.

1. Physical systems

The most common charging mechanism remains toll collection at booths located at the entry or exit of a charging zone. Regular users of the M4 near Bristol or M25 around Dartford are familiar with paying tolls to use the Severn and Dartford Crossings. There are countless other examples of tolled infrastructure in the UK and around the world. People who regularly drive in continental Europe (e.g. France and Italy) are used to motorway tolls, with charges based on the distance travelled on the tolled road.

Toll plazas can operate manually or automatically with coin bins. A recent innovation is the introduction of priority lanes for vehicles with an electronic tag that allows payment to be deducted automatically without a need to stop.

The systems are simple to operate and well understood. They are sufficiently flexible to accommodate different charges for categories of vehicle or driver. The disadvantage, when compared to the electronic methods, is that the charges are fixed for a specific piece of road or crossing, or for entry to a specific area; so they cannot relate directly to the level of congestion at the time. Toll collection also takes time. A charge to enter a city centre via toll booths is likely to cause unacceptable delay to drivers.

2. Permit systems

Drivers are required to buy a valid licence or permit to enter or drive within the charged area. Licence or permit holders are then registered on a central database. Manual enforcement is applied by traffic wardens or police. Electronic enforcement uses automatic number plate recognition (ANPR) technology via cameras located at cordon entry points or in mobile locations throughout the charging area.

Permits can cover any time period from a single day (in the case of London) through to monthly, quarterly or annual versions. Flexibility within the system allows different permits for different categories of vehicle or driver, although enforcement becomes more difficult as the range of permits increases.

The main advantage of a paper based system is that it is simple to introduce, needing a minimum of technology in its basic form. The main disadvantage is that it is fairly crude, especially in the case of quarterly or annual permits. This may, perversely, encourage some drivers to drive in for every journey in order to get the most out of their purchase.

3. Electronic systems

Microwave technology:

The illustration below shows how microwave technology operates. Cameras fitted on gantries read number plates passing vehicles. (The need for a smartcard to automatically deduct payment is optional.) Automatic number plate recognition (ANPR) technology detects non-tagged vehicles. Of the two electronic methods, microwave technology is by far the simplest. Its main disadvantage is that it requires gantries on every road at regular intervals, something that would soon become unmanageable on any large geographic scale or complex urban area. The use of lampposts has been ruled out as camera angles would not allow detection of every vehicle.

Global Positioning Satellite technology (GPS):

The illustration below shows how the technology operates. Unlike microwave technology, GPS requires no overhead gantries and the necessary satellites are already in orbit. However, there is still a need for fixed or portable enforcement cameras, although these do not need to be as regularly spaced. Even though this technology is far more complicated than using microwaves, it is the only realistic option for any large scale implementation of electronic charging. Again, the use of a smartcard to automatically deduct payment is optional.

The unit in the vehicle works like a car radio - it 'listens' for broadcasts from GPS satellites but does not send any signal back to them. Communication is one-way and private. The in-car receiver matches its position with an electronic map of charged areas and a list of charge rates. The appropriate data is then 'radioed' to a processing office for the user's bill to be produced.

GPS is already used for navigation in the road haulage, shipping and aircraft industries and, increasingly with in-car navigation systems.

"Assisted GPS" will feature in coming generations of mobile phones. It will incorporate new levels of accuracy in locating the phone's exact position and will allow retailers, for example, to call potential customers as they pass their doors.