Taxonomy and description
Types of charging method
Variations in charge
Most studies and applications are based on point charging in which a charge is levied to pass a point on a road. In this form it is similar to conventional toll systems. Several US Value Pricing applications adopt this approach, with charges to use dedicated lanes, and with exemptions for High Occupancy Vehicles. These have been referred to as High Occupancy Toll lanes.
A charge on a single road is likely to encourage traffic to divert to avoid it and is rarely used except to charge for the use of motorways, bridges and tunnels. Most point pricing systems therefore involve cordon charging (or toll rings) in which a series of charging points are established at all entries to a given area (often a city centre). It is possible to extend this concept to a series of concentric cordons, or cells, or a cordon combined with radial screenlines.
A variant of cordon charging is area charging (or area licensing) in which the charge is levied to use a vehicle within a defined area, rather than just to enter it. This will also control vehicle journeys wholly within the cordon, which are unaffected by cordon charging (and might as a result increase).
Both cordon charging and area charging introduce boundary problems. Through traffic will re-route around the cordon, and may increase congestion; drivers may park outside and walk, adding to environmental problems. Those just outside the cordon will have to pay to travel to the centre; those just inside will not. Drivers making long journeys across the cordon pay the same as those making short journeys. These discontinuities can be overcome by continuous charging systems, which charge for all travel within a defined area (such as a city). These can be based on:
Charging has the advantage of being very flexible. The following variations
have been considered:
In discussing the technology options available for the implementation of Road User Charging, one has to distinguish between the payment process and the enforcement process.
It is possible to operate cordon charging or area charging using simple pre-purchased paper licences. This system operated in Singapore for several years. However, enforcement has to be manual, and can be expensive, and drivers must spend time purchasing licences. Also the ability to vary charges is more limited.
A relatively low technology alternative is to use Automatic Number Plate Recognition (ANPR). Drivers purchase a permit, and their vehicle is then added to an electronic list; automatic cameras record vehicles crossing cordons (or within areas) and check number plates against the list. This is still only feasible for cordon charging and area charging and variations in charging are still limited.
Cordon charging systems in Singapore and Norway now use fully electronic systems (ERP) in which the vehicle has an on board unit, in which a smart card is inserted. When the vehicle passes a charging point, it is detected, interrogated to identify the on board unit, and a charge deducted from the smart card. Vehicles detected without an on board unit or smart card are photographed for enforcement purposes.
Time charging could operate in a similar fashion with the on board unit switched on to charge the smart card (at a specified rate per minute) when the vehicle enters the area and switched off when it leaves it, or when the engine is stopped.
Distance charging and delay charging would either need a link to the odometer in addition, or need to use GPS to identify vehicles' locations. GPS (Global Positioning Systems) (these are also known as Global Navigation Satellite Systems (GNSS)) are most appropriate for distance based charging systems but again ANPR is used to identify occasional users and to capture image-based evidence sufficiently reliably to be acceptable in court. It is likely that GNSS systems will become the accepted way to impose all forms of urban road charging in due course, particularly since they can also provide other services such as driver information systems. However the technology is still being developed and there are still technical issues in urban canyons (i.e. roads that are surrounded by tall buildings) which may limit the accuracy and precision of the system.
The traditional cash based toll collection systems (i.e. payment of tolls at a toll plaza) combine charging and payment into one event. For electronic charging methods, we need to differentiate between charging and payment. The charging and payment processes are strongly linked to the enforcement process, regardless of the choice of charging technology. It has been argued that the three electronic technologies described in the table below are not competitors, but should be regarded as complementary.
Dedicated Short Range Communication (DSRC) permits vehicles to be identified and localised for enforcement purposes. When the vehicle passes a charging point, it is detected, interrogated to identify the on board unit, and a charge deducted from the smart card. Vehicles detected without an on board unit or smart card are photographed for enforcement purposes and Automatic Number Plate Recognition (ANPR) technology is used to identify exempt vehicles or allow for enforcement.
A charging system cannot exist without enforcement. An enforcement strategy needs to be based on three fundamental objectives:
Technological Options for Implementation of Road User Charging