A working definition of interoperability when applied to ITS systems is:
The ability of ITS-based systems to provide services (data, information, and control commands) to other systems and to accept services from those other systems so that the inter-connected systems operate effectively together. Systems are interoperable when the ITS services are seamlessly provided in real-time including between different organisations and/or at different locations.
ITS interoperability is particularly important for integrated Road Network Operations and has relevance for the road user and the road network operator.
For a service to be interoperable three levels of interoperability must be addressed:
Where is interoperability needed?
Interoperability becomes an issue if a system is composed of both fixed and mobile subsystems. For example, on-board units in vehicles that travel across borders must be able to communicate with roadside equipment at different geographic locations.
The priority areas for interoperability are:
Traffic Management and Control: Cross border traffic management requires the exchange of traffic information among network operators and harmonised procedures for network management, for example where do adjacent network operators want to concentrate traffic flow? (See Data Communications)
Traffic and Traveller Information: Data originating from many different sources (roadside traffic sensors, traffic police data, user calls, traffic management centres) that are disseminated to the users by means of different systems (roadside VMS, radio, internet, on-board navigation equipment) must be harmonised in order to avoid conflicting information to drivers. For example, there should be convenient means available to the drivers to acquire traffic and travel updates in order to ensure seamless provision of TTI services across borders and consistency of the data and information provided to users. (See Information Exchange)
Electronic Fee Collection (EFC): Common EFC payment for cross-border travel requires on-board units that are able to communicate with transponders or road-side beacons at toll stations or at enforcement sites and it requires agreements between the toll operators about clearing procedures and security issues. (See Back Office Arrangements and Enforcement)
Incident and Emergency Handling: In emergencies, travellers should be able to call services with their own equipment (cellular phone, on-board emergency system) no matter in which country they travel, and the emergency services should be able to find the relevant information about the vehicle, the persons and freight carried no matter what the origin of the vehicle. Automatic emergency call systems such as Europe's emerging e-call system are designed to notify incidents and accidents as they occur directly to a designated control facility. (See Driver Services)
Cross Border Enforcement: It is important to ensure that the enforcement of road traffic violations can be applied effectively and fairly to all road users, in the context of improving road traffic safety. (See Enforcement Systems and Policing / Enforcement) The increase of inter-regional and international traffic calls for cross border enforcement solutions that are interoperable and adhere to the following principle wherever possible:
“…all actions in the enforcement chain up to the enforcement of any penalty should be conducted by relevant agencies in the Region/ State where the violation is committed. Enforcement of any penalty should be carried out by the Region/ State where the vehicle is registered.”
Cross border enforcement solutions need to address:
The disadvantages associated with interoperability are:
The benefits of interoperability are:
A particular issue for all interoperable systems is what to do about non-equipped users, specifically those vehicles that should use a service but do not carry the proper interoperable equipment. In some regions (as in the EU) the road network operator is obliged to ensure non-discrimination of foreign users and solutions must be offered to ensure that a manual procedure is offered for the same function.
Interoperability and standardisation are very important to guarantee a nationwide or even cross border functionality in road network operations and effective use of ITS. There are three institutional layers involved:
Governmental and inter-governmental layer: This covers harmonisation of the road traffic regulations and in particular the technical requirements for vehicles and on-board equipment through the Vienna convention on road vehicles, OECD regulations and EU directives, including harmonisation of driver education with respect to Human Machine Interface (HMI).
Standardisation: The key to interoperability is standardisation. Only when interfaces are standardised can the different subsystems inter-work to carry out a particular function. Standards must include test procedures so that equipment can be certified by the operators for interoperable use. (See ITS Standards)
For network operators the following standardisation bodies are of particular importance:
Business to business agreements: the vehicle manufacturers and the electronics industry have been working together for a long time towards the development of interoperable systems. However, there are business cases where a strong commercial interest exists for excluding competitors from entering an established system.