Understanding real-time passenger information feeds: the SIRI standard

In the current digital landscape, everything is real-time: Email, WhatsApp, news, weather, even voting for TV shows! These days passengers expect operators to deliver applications that behave in the same way as all other their favourite mobile apps, providing up to date information at their fingertips, in real-time.

The term “real-time” can have a different meaning depending on the context. In the case of critical systems like airbag inflation, real-time means that detection of a collision and airbag deployment should occur within milliseconds. When talking about real-time passenger information systems (RTPI) however, we can safely assume that working larger time spans such as minutes is often enough.

In order to make real-time transport information compatible between different systems, several European countries joined efforts to create a standard protocol known as Service Interface for Real Time Information (SIRI). This protocol describes (at length!) how different systems can share real-time passenger information, allowing different suppliers, operators and municipalities to work together without costly development bills every time one of the party is swapped out.

At Passenger, we integrate SIRI feeds from third parties to display the Estimated Time of Arrival (ETA) on the departure/arrival boards within our mobile apps and provide live bus tracking on interactive route maps. There are 2 main parts of the SIRI specification that we use for this, which combine both Automated Vehicle Location (AVL) systems and ETA prediction engines.

Vehicle Monitoring (SIRI-VM) provides a vehicle-centric view of transport data.

AVL systems provide the GPS coordinates where a vehicle actually is with some periodicity (e.g. approximately every 30 seconds). These require vehicles to be equipped with a GPS receiver and mobile broadband connection. The location is sent to a central server, which then provides a live feed for all vehicles. SIRI-VM can also include further information about upcoming stops, such as the vehicle’s Estimated Time of Arrival (ETA).

Providing a map with live tracking of vehicles is also possible thanks to the SIRI-VM feed. This feature is very attractive to operators for monitoring the health of their network and also to their passengers as they can take more informed decisions about their travel arrangements.

Stop Monitoring (SIRI-SM) is a feed for the Estimated Time of Arrival (ETA) of a vehicle to a particular stop.

A SIRI-SM feed needs a prediction engine that blends AVL and other sources of information like timetables, geography and roadworks to provide an estimated time of arrival at each stop along the journey. Digital departure boards can be updated on a real-time basis, as vehicles progress along their routes.

Being an estimate, the ETA may not reflect the reality very accurately (e.g. due to unforeseen circumstances like a traffic incident), leading to the bus arriving late or sometimes early. At Passenger, we understand the frustration of missing a bus or waiting for too long at the stop, so we are currently working on better ways to display the uncertainty of the estimates.

Delivering this real-time information at high quality can sometimes be a struggle for operators but Passenger works alongside your SIRI systems to provide reliable, direct channels for this data to the people who need it. If you are interested in providing real-time information to your passengers, please get in touch.