> ## Documentation Index
> Fetch the complete documentation index at: https://docs.bayareatransit.dev/llms.txt
> Use this file to discover all available pages before exploring further.

# Realtime data

> SIRI-based stop and vehicle state, plus discontinued and future-looking service families.

## StopTimetable

`stoptimetable` is the scheduled departures surface for a stop within a requested departure window. It is a stop-centric scheduled view rather than a route-centric timetable view.

## StopMonitoring

`StopMonitoring` provides current and forthcoming arrivals and departures at a stop.

<Warning>
  The transit specification warns that omitting the stop filter can lead to very slow responses because the service may return all monitored stops for an agency.
</Warning>

## VehicleMonitoring

`VehicleMonitoring` provides the current location and expected activities of a vehicle, along with current and subsequent journey context.

```mermaid theme={null}
classDiagram
  class StopMonitoringDelivery {
    monitoredStopVisit[]
  }
  class MonitoredStopVisit {
    recordedAtTime
    monitoredVehicleJourney
  }
  class MonitoredVehicleJourney {
    lineRef
    vehicleRef
    framedVehicleJourneyRef
    monitoredCall
    vehicleLocation
  }
  class MonitoredCall {
    stopPointRef
    aimedArrivalTime
    expectedArrivalTime
  }
  class VehicleMonitoringDelivery {
    vehicleActivity[]
  }
  class VehicleActivity {
    recordedAtTime
    monitoredVehicleJourney
  }
  class VehicleLocation {
    longitude
    latitude
  }
  StopMonitoringDelivery "1" --> "*" MonitoredStopVisit
  MonitoredStopVisit "*" --> "1" MonitoredVehicleJourney
  MonitoredVehicleJourney "1" --> "1" MonitoredCall
  VehicleMonitoringDelivery "1" --> "*" VehicleActivity
  VehicleActivity "*" --> "1" MonitoredVehicleJourney
  MonitoredVehicleJourney "1" --> "1" VehicleLocation
```

## Other SIRI service families in the PDFs

The transit specification also documents several additional SIRI families that are not presented as stable primary surfaces here:

* **Announcement**: documented as discontinued
* **General Announcements**: documented as discontinued
* **Transit Schedule Updates**: documented as possible future implementation using SIRI Production Timetable
* **Transit Addition and Cancellation of Trips**: documented as possible future implementation using SIRI Estimated Timetable

## Message structures

Appendix C of the transit specification is the best source for the nested SIRI message structures behind realtime responses. It covers stop monitoring, vehicle monitoring, stop timetables, announcements, schedule updates, estimated timetables, general messages, and service alerts.