While that seems like a good start it seems like you would want to supplement that approach with the GTFS and GTFS-realtime feeds from transit agencies where av

While that seems like a good start it seems like you would want to supplement that approach with the GTFS and GTFS-realtime feeds from transit agencies where available. Having worked for a company that provided transit software I am well aware that GTFS-realtime data isn’t always accurate (especially the ETAs). But it seems like combining their ETA estimate with yours and the scheduled arrival time would be a reasonable approach. Or if you just started building a model of the average speeds of the bus on each link using the GTFS-r speed and location data you could probably build up a pretty good historical model of the traffic flow between 2 stops at any given point during the day. Yes, I am aware that scheduled times in transit can be meaningless. There are a lot of factors that contribute to that from traffic to poor schedule planning. They can however be a useful baseline estimate.