Terminology
Regulatory restrictions target to limit car use in urban areas as ways of access control into a particular area (often a city centre). "Regulatory" means legal measures based on the road traffic laws or the air pollution control laws but not including the pricing methods like urban road charging. Freight vehicles like the lorry may be exempted from regulatory restrictions. The lorry may also be controlled by other measures covered in Lorry routes and bans. Although the concept of "Car-free" or "Car-limited" is involved in regulatory restrictions, it has multiple measures which contain physical restrictions on car use and an improvement in the environment for pedestrian areas.

Types of Regulatory Restrictions
Two main types are in use: permits and number plate restrictions.

Permit systems operate to ban certain types of traffic from entering a defined area during specific time periods by the issue of permits. Usually private vehicles from outside the area and through traffic are discouraged, whilst residents' vehicles within the area and service and commercial vehicles are usually exempted from restrictions since they can be justified to be essential in a city centre. The category of vehicles and people who qualify for such exemptions are determined by local or municipal authorities.

Number plate restrictions are usually operated as the odds and evens system, in which vehicles with odd number plates and those with even number plates are admitted on alternate days determined by a day of the week or date. The system in Sao Paulo is based on the last digit of the number plate, where for example the vehicles prohibited from driving on Monday are those whose number plates have as their last digits either 1 or 2. Some categories of vehicles and people are also exempted in number plate restrictions.

Both types are implemented not only regularly but also temporarily. The regular measures are usually operated either weekday or weekend or everyday. The temporary measures are implemented on days in excess of threshold of an air pollution level, or for specific events such as a Car-free day. Number plate restrictions are usually used for the temporary measures because they are easier to enforce than permit systems. Hours of enforcement are usually working hours (e.g. 9:00 a.m. to 5:00 p.m.), but sometimes are only morning and evening peak hours.

Technology
Regulatory restrictions are required to manage whether each vehicle is allowed to drive in a defined area. The design of the checking points into and within an area is very important. When temporary regulatory restrictions are implemented during a specific time such as one day or a specific period like one season, municipal police or the authority establish access control points at the entrances into a given area wide or on screenlines within it and check the number plate or the category of vehicles to be permitted. Most applications of permanent measures (often permit systems) are based on point checking in which a check is operated on the entrance into the area by using paper licenses. Conventional message signs are also used to alert drivers. This traditional system is operated in many cities. Simplicity of administration, prevention of misuse and ease of enforcement have to be considered when designing the arrangements for these vehicles.

An applicable access control technology was developed in the 1990s and operated in some European cities. Drivers who have a permit can pass the toll without stopping. There are a number of options for technologies (Miles et al, 1998):

Video-based systems - Optical Character Recognition (OCR) and a permitted list. Use of number plate recognition requires suitable camera positions to provide number plate visibility and adequate lighting. For example, the number plate of a car following close behind a large vehicle may never be in the direct view of the camera.

Sophisticated non-stop tolling technology with communications capable of handling large data volumes at very high vehicle speeds. These systems are very effective, but environmentally intrusive and costly. Vehicles must be equipped with on-board transceivers or tags and video enforcement is also necessary, so implementation costs are high.

Simpler methods of selective vehicle detection as used for bus priority may be adequate if the numbers to be equipped are relatively small.

A magnetic or smart card pass that has to be manually inserted by the driver into a slot or through a contactless reader is a cheap but slow option.

A barcode sticker and reader located at the side of the road uses established technology, but is likely to be slow.
Similar technologies are reviewed in urban road charging.