nselikoff
commented
5 years ago These are important questions and a great opportunity for making TheTransitClock more dynamic and valuable.
VehicleEvents where eventtype = "No match" could be used as the initial trigger. Currently you have to differentiate these events between schedule adherence out of bounds (not a detour) and N bad spatial matches in a row (likely a detour).
Whatever underlying structures are developed to support detours / dynamic re-routing, they should definitely support translation into GTFS-realtime. For example, the current GTFS-realtime spec supports trips with status "Added" or "Canceled", and StopTimeUpdates with status "skipped". I would also recommend checking out the GTFS-ServiceChanges proposal and discussion, which would be a new extension covering more dynamic re-routing including changing shapes, and creating new stops, routes and trips on the fly.
scrudden
barbeau
vsperez
If there is a detour that is not in the GTFS schedule how should it be handled?
We would have to know it is there to be able to do something about it. So the question is how do we know it is there? If a vehicle goes on a detour it will, I presume, miss some of the normal stops for the trip. Can we detect this? Well, we can detect stops that have yet to have a vehicle pass it today. Does this indicate a detour? No, what about the first vehicle of the day. What if we say if no vehicles past it for the last X trips that were supported to pass it then it is a detour.
Oh, but to be a detour the vehicles must come back to the route. We will need to check this for the last X trips. We need to check that their next arrivals on the route are at the same stop.
So if we know the stop is detoured what should we do? Stop prediction passed this stop as we do not know how long the detour is? That's OK but the people waiting at the stops past the detour will not see any prediction for the vehicle so think it does not exist.
Just keep showing predictions as normal. This means that they will be incorrect for the passengers after the detour but at least the bus will exist. It will disappear though when it is on the detour as it will no longer match to the route.
The other option is to try and predict the travel time for the detour based on the time taken by the last X vehicles that took the detour.