GTFS and GTFS Realtime

Transit agencies use the General Transit Feed Specification (GTFS) to tell passengers' software, most often trip planners, what they run and when.^1,2 More than 10,000 agencies in over 100 countries use it, by gtfs.org's count.¹ It is maintained by MobilityData, a non-profit, with the help of the community; the specification itself lives in the google/transit repository on GitHub under the Apache 2.0 licence, and the gtfs.org site is CC BY 3.0.^3,5

GTFS began as a collaboration between TriMet in Portland, Oregon, and Google, to get TriMet's timetables into Google Maps, and was first called the Google Transit Feed Specification.³ It took its present name in 2010 as other software took it up.³ GTFS Realtime was added in 2011, and MobilityData was set up in 2019 to maintain it.³ It was designed to inform passengers about service, not to describe everything needed to run a transit operation.³

It has two parts. A GTFS Schedule feed is a ZIP file of simple text files.⁴ The basic seven are agency, routes, trips, stops, stop_times, calendar and calendar_dates.⁴ More than 15 optional files add fares, transfers, translations, paths inside stations and other details, and a GeoJSON file draws the areas served by demand-responsive services.⁴ A GTFS Realtime feed is encoded in Google's Protocol Buffers format, fetched with an ordinary web request, and always tied to a Schedule feed.^4,7 It carries four kinds of update.⁶ Trip updates give predicted arrivals, delays, cancellations and reroutes.⁶ Service alerts describe a closed station or a disrupted line.⁶ Vehicle positions say where each vehicle is, with its speed, odometer reading and congestion level.^4,6 Trip modifications describe detours that affect a set of trips.⁶

Feeds are found through MobilityData's Mobility Database, an open catalogue of more than 6,000 GTFS, GTFS Realtime and GBFS feeds from over 100 countries with a REST API, which also links validators for GTFS and GTFS Realtime feeds.⁸ Beyond trip planners, software uses GTFS to make timetables, to visualise data, for accessibility and for planning analysis.³ For a model of a place, a Schedule feed is the public transport network: where the stops are, which routes serve them and when.⁴ A Realtime feed adds where the vehicles are right now.⁶