relax the requirement for in-seat transfer to allow attach / detaching vehicles in the middle of a trip

[miklcct]

Describe the problem

Currently, the in-seat transfer says that:

The last stop of from_trip_id SHOULD be geographically close to the first stop of to_trip_id, and the last arrival time of from_trip_id SHOULD be prior but close to the first departure time of to_trip_id. The last arrival time of from_trip_id MAY be later than the first departure time of to_trip_id in case the to_trip_id trip is occurring the subsequent service day.

However, this modelling does not allow the specification where carriages are attached / detached in the middle of a trip, which is common in the National Rail network.

Use cases

I would like to model the joining / splitting of train services, where carriages are attached / detached not at the end / beginning of a trip, but instead, in the middle of a trip.

For example, a train trip runs from London Bridge to Caterham, and another trip runs from Purley to Tattenham Corner by detaching a portion from the London Bridge to Caterham trip.

Proposed solution

Relax the requirement of transfer_type = 4 to allow the transfer taking place between two trips, where the transfer stop is a terminus (start stop / end stop) for one of the trip, and any (including start / end / intermediate) stop for the other.

Additional information

No response

[gcamp]

For example, a train trip runs from London Bridge to Caterham, and another trip runs from Purley to Tattenham Corner by detaching a portion from the London Bridge to Caterham trip.

It wasn't the primary goal when we designed transfer_type = 4 but how we though this should be represented is with three trips :
Trip A : from London Bridge to Purley
Trip B : from Purley to Tattenham Corner
Trip C : from Purley to Caterham

Then you link with in-seat transfers A -> B, A -> C.

[miklcct]

For example, a train trip runs from London Bridge to Caterham, and another trip runs from Purley to Tattenham Corner by detaching a portion from the London Bridge to Caterham trip.

It wasn't the primary goal when we designed transfer_type = 4 but how we though this should be represented is with three trips : Trip A : from London Bridge to Purley Trip B : from Purley to Tattenham Corner Trip C : from Purley to Caterham

Then you link with in-seat transfers A -> B, A -> C.

The real-world modelling for this is two trips: London Bridge to Caterham and Purley to Tattenham Corner, which is how these trips are shown in all official and unofficial channels, unless they are specifically coded to display split / joins.