The short answer
Use SIRI when your National Access Point or partners require the European standard and you need its full range of services. Use GTFS Realtime when you want a compact feed that nearly every app can read. Many operators publish both.
Side by side
| SIRI | GTFS Realtime | |
|---|---|---|
| Origin | European standard (CEN) | Open, community-maintained format |
| Encoding | XML | Protocol Buffers (binary) |
| Content | Estimated timetables, vehicle and stop monitoring, situations and more | Trip updates, vehicle positions and service alerts |
| Exchange | Request/response or subscription | Typically a feed that consumers poll |
| Pairs with | NeTEx | GTFS |
| Size and speed | Larger, more verbose | Compact and fast to parse |
Choosing
Whichever you choose
- Keep identifiers stable and consistent with the timetable.
- Monitor uptime and latency. Real-time data that is late is worse than none.
- Document the profile, update frequency and licence in the metadata.
Next steps
See all data formats, NeTEx vs GTFS and static and dynamic data.
Frequently asked questions
Is GTFS Realtime a standard?
It is an open, widely used format maintained by a community. It is not a CEN standard like SIRI.
Which is more widely supported by apps?
GTFS Realtime is very widely supported. SIRI is the European standard and is required or preferred in many national contexts.