ISO/TS 17426:2016

- specifies the Contextual Speed Information Service, namely the general requirements regarding the provision of the Contextual Speed Information Service, the data flow supporting the service, and the presentation of the service result,

- specifies the requirements to be fulfilled by the Contextual Speed Information Service,

- specifies the ITS Station (ITS-S) application processes of the vehicle ITS station, roadside ITS station, central ITS station, and personal ITS station that are required to instantiate the Contextual Speed Information Service,

- specifies sets of communication requirements and objectives (profiles) using the methods defined in ISO 17423 to select the level of performance (best effort or real-time, etc.), confidence and security (authentication, encryption, etc.) for each Contextual Speed Information Service communication flow between ITS stations,

- selects relevant functions and procedures provided by the ITS station facilities layer (see ISO 17429), and

- specifies messages, messages sets structure, content, and syntax to be used by the Contextual Speed Information Service.

ISO/TS 17426:2016 considers the scenario for the transmission of Contextual Speed information from the infrastructure/roadside to the vehicle, for onward presentation to the vehicle's driver. This scenario foresees that the calculation of Contextual Speed information is performed on the Infrastructure side, not within the vehicle.

Mandatory speed limits or advisory speed recommendations are output of the Contextual Speed Information Service which (in the scenario considered in this Technical Specification) is run by the Road Operator in its Traffic Control Centre or comparable infrastructure (e.g. Roadside ITS Station). To transfer this information to the vehicle (and therefore the driver) over the air (wireless communication), defined messages are required. These messages are specified in this Technical Specification.

When Contextual Speed information arrives in the vehicle, further pre-processing might be necessary before the Contextual Speed information, and, if available, additional explanations on speed limits or recommendations, can be presented to the driver. This Technical Specification specifies the requirements that need to be fulfilled when processing the messages. It does not specify how the vehicle handles the incoming messages.

The production of information supporting this application, its qualification and its relevance are out of the scope of this Technical Specification.

ISO/TS 17426:2016 addresses Use Case 1 "Provision of mandatory speed limit information into vehicle ? for driver awareness purposes" and Use Case 2 "Provision of advisory speed information into vehicle ? for driver awareness purposes".