Introduction. Public transport services increasingly rely on information systems to ensure reliable, efficient operation and

Public transport services increasingly rely on information systems to ensure reliable, efficient operation and

widely accessible, accurate passenger information.

Well-defined, open interfaces have a crucial role in improving the economic and technical viability of Public

Transport Information Systems of all kinds. Using standardised interfaces, systems can be implemented as

discrete pluggable modules that can be chosen from a wide variety of suppliers in a competitive market,

connecting diverse systems; rather than as monolithic proprietary systems from a single supplier. Interfaces

also allow the systematic automated testing of each functional module, vital for managing the complexity of

increasing large and dynamic systems. Furthermore, with a well defined, version interface, individual

functional modules can be replaced or evolved, without unexpected breakages of obscurely dependent

function.

The SIRI framework is a European Technical Specification that provides a specification for a number of

functional interfaces that allow public transport data of specific types to be exchanged readily using structured

interfaces.

Furthermore, this European Technical Specification specifies an additional SIRI functional service to

exchange incident and event information about disruptions to public transport between servers containing

real-time public transport vehicle or journey time data. These include the control centres of transport operators

as well as information systems that deliver passenger travel information services.

DD CEN/TS 15531-5: 2011

CEN/TS 15531-5: 2011 (E)

Scope

The SIRI Situation Exchange service (SIRI-SX) allows the efficient exchange of data about situations caused

by planned and unplanned incidents and events and is intended to support the use cases identified in

Annex C. Situations are actual or potential perturbations to normal operation of a transport network. The SIRISX

service uses the common SIRI communication framework and services which are described in

CEN/TS 15531-1 and not repeated in this document.

The Situation Exchange service has a rich Situation model, allowing a structured description of all aspects of

multimodal travel Situations, including cause, scope, effect and rules for distribution to an audience. The

structured values enabling computer based distribution through a wide variety of channels, and the

presentation of data in different formats for different device and different audiences. The Situation Exchange

Service allows the exchange of incident and event information between, amongst others:

Control centres;

Operations staff;

Public information systems;

Alert systems and personalised alert systems;

UTMC systems;

Journey planners;

AVMS (Automatic Vehicle Management Systems).

SIR-SX uses a network model based on the CEN Transmodel conceptual model for public transport networks,

schedules and operations, along with the CEN Identification of Fixed Objects in Public Transport (IFOPT)

model for describing physical transport interchanges.

The Situation Exchange service is envisaged as a 'back office' capture and exchange service that will feed

other public facing travel information dissemination systems, in particular those using the TPEG format.

Transport Protocol Expert Group (TPEG) is a European Broadcasting Union fostered standard for

broadcasting travel data over Digital Assisted Broadcasting (DAB) radio and other channels. To this end, the

SIRI-SX situation classification model has been harmonised as far as possible with that of TPEG and DATEX2

so that full interoperability can be achieved. Uses of structured elements from TPEG, for which translations

already exist in most European languages, also facilitates human readability in different national languages.

Maintaining and improving a harmonisation with TPEG will be a continuing objective. In addition to the TPEG

exchangeable content, SIRI-SX messages contain additional structured information which allows them to be

processed in additional ways.

Situation and computer systems and applications are typically distributed, that is information will be captured

on one system and exchanged with others for dissemination and further processing. This means that a

message design is needed that allows the management of the identity of distributed messages over time and

across different systems, so that subsequent updates to a Situation can be reconciled by different systems

over a network, and obsolete messages can be retired automatically. The SIRI-SX situation model is designed

to support the distributed management of Situations.