In the single contract concept, - also called Single Contract Interoperability - the user signs only one single contract with a (European Electronic) Toll Service Provider. One interoperable OBU is installed into the vehicle. This concept is also favoured by the European Commission (see also Directive 2004/52/EC). Ways to implement such a concept have been investigated in a number of EU projects.

The concept of a single contract interoperability was and is the main issue of several EU sponsored projects. One of the most relevant project, named CESARE has defined the main entities for single contract interoperability. The roles are:

The Service user will subscribe to a European Toll Service provided by the EETS provider, allowing a vehicle to be used and charged anywhere within the European Union or only in the countries selected. The Service User pays the tolls or taxes to his EETS provider (and not directly to the Toll Chargers like in a Multi Contract Interoperability). The EETS provider will then settle accounts with each Toll Charger. The EETS provider is the users single interface to the European Toll Infrastructure and one OBE is installed in the vehicle of the Service User. The Service User has specific obligations, like for instance not driving on tolled roads if it indicates that it does not work properly. The Service User is expected to know when the vehicle was driving on which part of the road network.

Toll Chargers operate at least one local tolling system extending to a defined part of the road network and are responsible for levying the tolls or taxes. On a specific road several tolls possibly collected by different Toll Chargers may apply (like for instance a toll within a national tolling scheme and an additional toll for a specific object like a bridge or tunnel). The Toll Charger supports the EETS in all areas under his responsibility. For those vehicles under contract by an EETS Provider, the Toll Charger receives the charging data and - based on the date received - claims payments from the corresponding EETS
Provider. The Toll Charger is also responsible for all Toll Enforcement Activities.

EETS Providers offer an European Electronic Toll Service (EETS). They provide service contracts, on-board units (OBU) for electronic toll collection as well as payment means to the Service Users subscribed to the EETS. They collect the payments of tolls and taxes from their customers and guarantee the payment of the services dues towards the Toll Chargers. EETS Providers authorise service points to install the OBU in the vehicles and to personalise the OBE. Through their service points EETS Providers are also responsible for the correctness of the personalised data stored in the OBU.

The Interoperability Manager will be the regulatory entity - possibly established by the European Commission - which will ensure the interoperability between the European Toll Schemes on the technical, organisational as well as the contractual level. This entity will establish and enforce rules for interoperability, id-schemes, certification, common specifications and more.