The Pulse of Transit: EN 15531 (SIRI) & Real-Time Data Standards

What is EN 15531?

EN 15531, widely known by its acronym SIRI (Service Interface for Real-time Information), is the European Standard that defines how computers exchange real-time status information about public transport services.

While NeTEx handles the “planned” world (scheduled timetables), EN 15531 handles the “actual” world (delays, cancellations, and live locations). It specifies a standardized XML protocol allowing an operator’s control system (AVMS) to push live updates to passenger information displays, mobile apps, or other transport authorities. It is the digital nervous system that powers the “Next Train in 2 Minutes” signs on platforms across Europe.

The Architecture of SIRI

EN 15531 is based on the Transmodel (EN 12896) conceptual framework. It uses a Publish/Subscribe mechanism: a consumer (e.g., a journey planner app) subscribes to a specific data feed, and the producer (the railway operator) publishes updates only when the status changes.

The standard is modular, consisting of several specific functional services:

• Stop Monitoring (SM): Provides the estimated arrival and departure times for vehicles at a specific stop (used for platform displays).
• Estimated Timetable (ET): Provides real-time updates to the schedule for a specific line or journey (e.g., “Train 123 is running 10 minutes late”).
• Connection Monitoring (CM): Facilitates “connection protection” by allowing feeder trains to request a connecting service to wait.
• General Message (GM): Distributes unstructured information, such as “Elevator out of service” or “Station closed due to security.”

SIRI in the Railway Sector

For railways, EN 15531 is critical for intermodal travel. It allows a national railway operator to receive live bus data to display on train station screens, or to send train delay data to a regional bus operator so the bus waits for the late train. It is the technical enabler for seamless travel chains.

Comparison: EN 15531 (SIRI) vs. GTFS-realtime

A common question in the industry is the difference between the European Standard (SIRI) and the Google-backed format (GTFS-rt).

The Dynamic Duo: SIRI and NeTEx

EN 15531 is rarely used in isolation. It relies on the static identifiers (Stop IDs, Journey Patterns) defined in NeTEx (CEN/TS 16614).

Example: NeTEx says “Train 900 scheduled at 12:00.” SIRI says “Train 900 is delayed +5 minutes.” Without the static NeTEx definition of “Train 900,” the SIRI message is meaningless. Together, they form the complete EU framework for Intelligent Transport Systems.