Although the situation may vary between different jurisdictions, the enforcement of traffic regulations often becomes relevant to the operations of the network. To ensure a smooth network flow, road users are expected to comply with regulations. Unless those regulations are self-enforcing (for example speed control through traffic calming measures) there needs to be a way to enforce the regulations.
Enforcement is not new – but recent technological advances have enabled new methods of automatic enforcement. The use of digital imaging and image processing, such as automatic licence plate recognition has had a dramatic impact.
Enforcement methods using new technology involve some kind of automatic detection. Sensors and digital cameras make it possible to better detect offences in speeding, red light violations and other evasions. The role of applying penalties is generally undertaken by an organisation responsible for enforcement (usually the police). The biggest benefit of these monitoring systems is said to be their deterrent effect. Enforcement systems are unpopular but will generally cause most users to become more cautious – increasing safety and improving the general throughput of the network. (See Policing / Enforcement and Law Enforcement)
One of the most frequent uses of automatic enforcement is the enforcement of speed limits using speed cameras. This requires a specialised speed camera that will measure the speed of each vehicle. In many cases, the system simply displays the speed to bring it to the driver’s attention, which is often enough to encourage them to reduce speed. In other situations, the system will take a picture of the offending vehicle for follow-up action. This would usually include capturing the number-plate of the car – but in some cases, it is necessary to include the picture of the driver, since in many countries, the vehicle owner may not be liable for actions by someone else using the vehicle.
The speed enforcement system can be permanent or a mobile unit. The information acquired by it will be used by the enforcement agency to apply penalties or (if necessary) prosecute the offender. Point-to-point journey times can be monitored by installing two cameras that are linked. Average speed monitoring is now commonplace, especially to regulate traffic speeds over extended sections, such as work zones. (See Speed Management)
Red light evasion ("red light running") at traffic signals can lead to serious accidents and it is extremely important that the traffic lights are observed. If non-compliance is high police presence or automated camera enforcement are two options. Automatic systems use a speed sensor (inductive loop) embedded in the road and a camera installed under the traffic signals. The red light and the vehicle sensor together will activate the camera and a picture taken of the offending vehicle. More advanced systems use the camera both to detect violations and to photograph the offence.
Where a railway (railroad) crosses a road or highway at a level crossing (“at-grade" crossing) there is always a potential safety issue. The level of protection varies considerably between different countries and regions. Where they are protected by gates, flashing lights or barriers – there is often in addition enforcement systems aimed at improving safety. For example, rather like red light traffic signal evasion, if a road vehicle enters a rail intersection during a warning period, it will be photographed.
ITS technologies are being explored to develop systems which can detect potential road/rail vehicle conflicts and help prevent collisions. For example, an Australian team is trialling an in-vehicle collision alert system which uses GPS and Dedicated Short Range Communications (DSRC) to warn vehicles if a train is approaching a crossing.
Heavy vehicles (trucks in particular) are often driven continuously by a single driver, accidents often result from fatigue. In many countries, there are regulations that specify the maximum amount of continuous driving time that is permitted. In order to enforce this, a black-box or electronic tachograph that detects the axle movement and possibly the location of the vehicle along time is often used. (See Driver Safety)
Since the road can only take a certain amount of weight per axle, it is important to ensure that all vehicles are not overloaded and are within legal limits. Otherwise, there will be significant deterioration of the road structure. Weigh-in-Motion (WiM) systems use a sensor on the road to measure each vehicle’s axle weight. When an overloaded vehicle passes, it will be notified to the enforcement agency which will take appropriate measures. (See Weight Screening)
Since most of violations may be contested in court, the systems must be adapted to meet the legal requirements of each country. In some cases, only the vehicle number-plate (licence plate) is necessary to catch the offending vehicle, while in others, the actual driver must be identified. For these systems to be effective and have the desired deterrent effect, they need to collect information that can stand up in court. Equipment must be type approved to certify that it operates to the required standard of accuracy and reliability. Type approval is important to avoid a legal challenge based on inadequate equipment and procedures. (See Equipment Certification)
Privacy is another important issue. It is extremely important to keep records confidential. In the case of identifying and notifying offenders, it may be necessary to capture photographs of offenders, which may lead to privacy concerns. (See Privacy)
One of the most difficult issues in implementation is proper coordination between the enforcement agency and the road network operator. In many countries, the road operators do not have the power to enforce regulations (this is usually police work). It is important to establish good working relations with the traffic police, to ensure that enforcement activities will facilitate better operation of the network.