We try to be as open as possible nowadays. However, these backend systems are from an old proprietary contract. There's a computer with a GPS receiver and driver UI in each bus and tram sending the MQTT messages to mqtt.hsl.fi (IBM MessageSight hardware for now) over 3G cellural data connection.

The subway can't use GPS but the trains read RFID tags installed along the tracks and there's wifi coverage. The suburban trains have Raspberry Pi's listening in promiscuous mode in the maintenance Ethernet ports and relaying the vehicle data to us.

The ferries send AIS radio data that we fetch from here: https://meri.digitraffic.fi/api/v1/metadata/documentation/sw...

The REST API is part of Digitransit, which is a fully open passenger information platform and journey planner. Docs and code here: https://digitransit.fi/en

Specifically, the switchbox for realtime data is a simple NodeJS application: https://github.com/HSLdevcom/navigator-server