Tag: Public Transport

Bringing Swiss Public Transport Departures to Grafana

de en

The Swiss Railways (SBB) provide a collection of static data sets and dynamic APIs at opentransportdata.swiss. One endpoint provides a list of departures or arrivals for a given train, bus or tram station.

In this blogpost, I'm showing you how I'm using this API to get a list of upcoming departures for the station next to my home, and how do get this list into Grafana.

The API

The XML API is documented in the "API Cookbook". A request looks like this:

POST /trias HTTP/1.1
Host: https://api.opentransportdata.swiss
Authorization: TOKEN
Content-Type: text/xml

<?xml version="1.0" encoding="UTF-8"?>
<Trias
    version="1.1"
    xmlns="http://www.vdv.de/trias"
    xmlns:siri="http://www.siri.org.uk/siri"
    xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance">
  <ServiceRequest>
    <siri:RequestTimestamp>  NOW  </siri:RequestTimestamp>
    <siri:RequestorRef>EPSa</siri:RequestorRef>
    <RequestPayload>
      <StopEventRequest>
        <Location>
          <LocationRef>
            <StopPointRef>  BPUIC  </StopPointRef>
          </LocationRef>
          <DepArrTime>  NOW  </DepArrTime>
        </Location>
        <Params>
          <NumberOfResults>  N_RESULTS  </NumberOfResults>
          <StopEventType>departure</StopEventType>
          <IncludePreviousCalls>false</IncludePreviousCalls>
          <IncludeOnwardCalls>false</IncludeOnwardCalls>
          <IncludeRealtimeData>true</IncludeRealtimeData>
        </Params>
      </StopEventRequest>
    </RequestPayload>
  </ServiceRequest>
</Trias>

This request is fairly minimal; it is limited to a single station, and without further information such as previous and following stops. You only need to fill in the following arguments to make this work for your station of choice:

  • TOKEN: API Token, need to register an account.
  • NOW (2x): Current time in ISO-8601 form.
  • BPUIC: Numeric ID of the station ("Betriebspunkt"), can be looked up in the DiDok dataset.
  • N_RESULTS: Maximal number of results to return.

Prometheus Ingestion

XML is a bit... let's say, uncomfortable to handle in Bash scripts, so I resorted to using the xsltproc tool to transform the API response into something easily iterable; the XSLT document i came up with looks like this and generates CSV content:

<?xml version="1.0" encoding="utf-8"?>
<xsl:stylesheet
    version="1.0"
    xmlns:xsl="http://www.w3.org/1999/XSL/Transform"
    xmlns:trias="http://www.vdv.de/trias">
  <xsl:output method="text" />
  <xsl:template match="/">
    <xsl:for-each select="//trias:StopEvent">
      <xsl:value-of select="trias:Service/trias:PublishedLineName/trias:Text"/>
      <xsl:text>;</xsl:text>
      <xsl:value-of select="trias:Service/trias:DestinationText/trias:Text"/>
      <xsl:text>;</xsl:text>
      <xsl:value-of select="trias:ThisCall/trias:CallAtStop/trias:ServiceDeparture/trias:TimetabledTime"/>
      <xsl:text>;</xsl:text>
      <xsl:value-of select="trias:ThisCall/trias:CallAtStop/trias:ServiceDeparture/trias:EstimatedTime"/>
      <xsl:text>&#x0A;</xsl:text>
    </xsl:for-each>
  </xsl:template>
</xsl:stylesheet>

Each line in the result represents a stop at the station, with the following fields:

  1. Number of the train or bus line
  2. Name of the destination
  3. Scheduled departure time
  4. Estimated/actual departure time

This format is quite easy to handle in Bash; let's parse the ISO-8601 timestamps, compute the delay for each stop and then emit the results in Prometheus collector format:

# TYPE sbb_station_departure gauge
# HELP sbb_station_departure Departures from a train or bus station
# TYPE sbb_station_delay gauge
# HELP sbb_station_delay Departure delay
sbb_station_departure{line="26",planned="1580875380000",destination="Erstfeld"} 1580875380000
sbb_station_delay{line="26",planned="1580875380000",destination="Erstfeld"} 0
sbb_station_departure{line="36",planned="1580875980000",destination="Zürich HB"} 1580875980000
sbb_station_delay{line="36",planned="1580875980000",destination="Zürich HB"} 0

I'm using the Textfile Collector feature of the Prometheus Node Exporter to ingest this document into Prometheus.

Display in Grafana

I'm showing this data in a table panel in Grafana, using two queries: one for the scheduled departure, one for the delay. Here, you can filter the departures by destination, if not already done in your script:

min without (__name__) (sbb_station_departure{destination=~".*Zürich.*"})

and

min without (__name__) (sbb_station_delay{destination=~".*Zürich.*"})

And finally, after some styling, the result looks like this:

Screenshot of a Grafana table panel with a train schedule

The code can be found on Gitlab.