HGTFS — Historical General Transit Feed Specification
A GTFS-based specification for historical transit networks: stops, routes, edges and operators with explicit time-of-validity (date_opened / date_closed), honest date uncertainty, a network graph, and historical-context events.
GTFS describes today’s transit networks; HGTFS is the equivalent for
historical ones. Every stop, route, network edge and operator carries an
explicit time-of-validity, so a network can be reconstructed for any chosen
date — and where the historical record is uncertain, the dates say so
(date_opened bounded by min/max, closures asserted only on evidence).
The specification is developed in the open at hgtfs.github.io — a full field reference plus a time-aware web viewer that scrubs a feed through time and recolours the network as operators change. It grew out of the earlier, archived openhistorymap/HTFS draft and is the basis for transit layers inside OHM.