ISO/TS 17426:2016

TECHNICAL ISO/TS
SPECIFICATION 17426
First edition
2016-03-15
Intelligent transport systems —
Cooperative systems — Contextual
speeds
Systèmes intelligents de transport — Systèmes coopératifs — Vitesses
contextuelles
Reference number
©
ISO 2016
© ISO 2016, Published in Switzerland
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ii © ISO 2016 – All rights reserved

Contents Page
Foreword .iv
Introduction .v
1 Scope . 1
2 Conformance . 2
3 Normative references . 2
4 Terms and definitions . 2
5 Symbols and abbreviated terms . 3
6 Contextual Speeds: Architecture . 4
7 Contextual speeds: Use cases . 5
7.1 General . 5
7.2 Use case 1: Provision of mandatory speed limit information into vehicle – for
driver awareness purposes . 6
7.3 Use case 2 - Provision of advisory speed information into vehicle – for driver
awareness purposes .10
8 Contextual speeds: Roles and responsibilities .14
8.1 Scenarios for contextual speeds .14
8.2 System operation roles in scenario 7 .15
8.3 Possible actors in the Contextual Speed Information Service .15
9 Contextual speeds: Characteristics.16
10 Contextual speeds: General service requirements .16
11 Contextual speeds: Communication requirements .17
11.1 General .17
11.2 General communication requirements .18
11.2.1 General.18
11.2.2 ITS-S application processes of the Contextual Speed Application .18
11.2.3 Flow types of the Contextual Speed Application .18
11.2.4 Flow Type 1 of the Contextual Speed Application .19
11.2.5 Flow Type 2 of the Contextual Speed Application .19
11.2.6 Flow Type 3 of the Contextual Speed Application .20
11.2.7 Sources and Sink ITS stations of the Flow Types .21
11.2.8 Other general communication requirements .21
11.3 Application specific data element requirements .21
Annex A (normative) Contextual speeds: IVI Profile (Definition of CSM) .23
Bibliography .29
Foreword
ISO (the International Organization for Standardization) is a worldwide federation of national standards
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The committee responsible for this document is ISO/TC 204, Intelligent transport systems.
iv © ISO 2016 – All rights reserved

Introduction
Traditional fixed speed limits have, in general, been set as the maximum mandatory speed that a
vehicle or a category of vehicles can travel at. Such speed limits are defined by the competent authority.
Some national authorities moderate mandatory speed limits when road or environment conditions
change. When road or environmental conditions change, the decision as to the most appropriate speed
a driver or rider should travel is, in general, left up to the individual vehicle driver. With the advent of
Cooperative Intelligent Transport Systems (ITS), it has become possible to provide better guidance to
vehicle drivers on what speed they should travel at when road, traffic, or environmental conditions are
less than ideal. This function is known as Contextual Speed Information Service.
Delivering Contextual Speed information to road users can improve road safety, support traffic
management, and reduce greenhouse gas emissions.
In a Cooperative ITS environment, Contextual Speeds are context-dependent (e.g. changed due
to weather conditions), as well as time-specific and road section-specific speeds. Subject to local
regulations, they can be mandatory speed limits or advisory speeds.
All Cooperative ITS Services follow the same abstract structure of detection (of an event) including pre-
processing of the detected content, execution of the Service algorithm (processing of detected content)
and presentation or utilization of the Service result. Figure 1 summarizes and further illustrates this
process.
Content processing
Detection
Info service generation
Info service presentation
Figure 1 — General Cooperative ITS Service process (from ISO/TS 17427:2014, Figure A.6)
Based on this abstract process description, for any Cooperative ITS Service, a similar process description
applies to the Contextual Speed Information Service. Every single step in the process chain can be
executed by different actors or stakeholders. Execution of process elements by different stakeholders
results in a large number of possible potential scenarios. Additionally, the involvement of stakeholders
can be distinguished by spatial geography.
Assuming that there are two main stakeholder groups in Cooperative ITS, namely the Infrastructure
and the Vehicle, multiple combinations are possible, as every step can be delivered by a different
stakeholder group (see Figure 2).
Figure 2 — Possible scenarios — Simple
The scenarios address different combinations; the basis for every scenario is one specific combination.
This Technical Specification addresses the scenario where detection, content pre-processing, and
information service generation is the responsibility of the infrastructure stakeholder. The direct
presentation of Contextual Speed information on the driver interface of the vehicle is out of the scope
of this Technical Specification. This Technical Specification therefore addresses only part of the whole
process (Scenario 7).
Within the context of Scenario 7, this Technical Specification 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”.
This does not preclude other Use Cases or deployment models in later Technical Specification(s).
vi © ISO 2016 – All rights reserved

TECHNICAL SPECIFICATION ISO/TS 17426:2016(E)
Intelligent transport systems — Cooperative systems —
Contextual speeds
1 Scope
This Technical Specification
— 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.
This Technical Specification 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, a
...