Real-time train positions for 17 cities, built from public GTFS-RT feeds [OC]

I built this because MetroBoard was $200, had a months-long waitlist, and only does one city. This one does 17, runs in the browser, and costs nothing beyond hardware I already had. Every dot is a live train pulled from GTFS-RT feeds that transit agencies publish publicly. I process the static feed once into route [...]