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Update min_transfer_time requirement for transfers #668

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Update min_transfer_time requirement for transfers #668

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Update min_transfer_time requirement for transfers
skalexch Oct 19, 2026
a499b7c
add transfe type 5 to forbidden min_transfer_time
skalexch Nov 6, 2026
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2 changes: 1 addition & 1 deletion gtfs/spec/en/reference.md
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Expand Up @@ -694,7 +694,7 @@ For a given ordered pair of arriving trip and departing trip, the transfer with
| `from_trip_id` | Foreign ID referencing `trips.trip_id` | **Conditionally Required** | Identifies a trip where a connection between routes begins.<br><br>If `from_trip_id` is defined, the transfer will apply to the arriving trip for the given `from_stop_id`.<br><br>If both `from_trip_id` and `from_route_id` are defined, the `trip_id` must belong to the `route_id`, and `from_trip_id` will take precedence.<br><br>Conditionally Required:<br>- **Required** if `transfer_type` is `4` or `5`. <br>- Optional otherwise. |
| `to_trip_id` | Foreign ID referencing `trips.trip_id` | **Conditionally Required** | Identifies a trip where a connection between routes ends.<br><br>If `to_trip_id` is defined, the transfer will apply to the departing trip for the given `to_stop_id`.<br><br>If both `to_trip_id` and `to_route_id` are defined, the `trip_id` must belong to the `route_id`, and `to_trip_id` will take precedence. <br><br>Conditionally Required:<br>- **Required** if `transfer_type` is `4` or `5`. <br>- Optional otherwise. |
| `transfer_type` | Enum | **Required** | Indicates the type of connection for the specified (`from_stop_id`, `to_stop_id`) pair. Valid options are:<br><br> `0` or empty - Recommended transfer point between routes.<br>`1` - Timed transfer point between two routes. The departing vehicle is expected to wait for the arriving one and leave sufficient time for a rider to transfer between routes.<br>`2` - Transfer requires a minimum amount of time between arrival and departure to ensure a connection. The time required to transfer is specified by `min_transfer_time`.<br>`3` - Transfers are not possible between routes at the location.<br>`4` - Passengers can transfer from one trip to another by staying onboard the same vehicle (an "in-seat transfer"). More details about this type of transfer [below](#linked-trips). <br>`5` - In-seat transfers are not allowed between sequential trips. The passenger must alight from the vehicle and re-board. More details about this type of transfer [below](#linked-trips). |
| `min_transfer_time` | Non-negative integer | **Conditionally Required** | Amount of time, in seconds, that must be available to permit a transfer between routes at the specified stops. The `min_transfer_time` should be sufficient to permit a typical rider to move between the two stops, including buffer time to allow for schedule variance on each route. <br><br>Conditionally Required:<br>- **Required** if `transfer_type` is `2`. <br>- Optional otherwise. |
| `min_transfer_time` | Non-negative integer | **Conditionally Forbidden** | Amount of time, in seconds, that must be available to permit a transfer between routes at the specified stops. The `min_transfer_time` should be sufficient to permit a typical rider to move between the two stops, including buffer time to allow for schedule variance on each route. <br><br>Conditionally Forbidden:<br>- **Forbidden** if `transfer_type` is `3` or `4`. <br>- **Required** if `transfer_type` is `2`. <br>- Optional otherwise. |

@jfabi jfabi Oct 30, 2026

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Is there a scenario when this field might be useful when transfer_type is 5? If not, should we forbid it as well?

@skalexch skalexch Nov 2, 2026

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@jfabi a transfer_type = 5 is one where thew riders have to re-board. Even if it's the same vehicle, there might be a case where a min_transfer_time is helpful. Maybe a train carriage being decoupled or coupled and it takes a specific amount of time. I think the major benefit is to forbid for cases that are clear contradictions.

@felixguendling felixguendling Nov 5, 2026

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I think that's not what we want?

If you set the min_transfer_time of a transfer_type=5 transfer to the time it takes to couple and decouple, a real-time update that moves arrival and departure closer to each other will break the transfer. A routing engine would not produce the transfer despite it being viable.

@skalexch skalexch Nov 5, 2026

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@felixguendling I guess the only reason to add it is to describe a minimum theoretical time it takes to do the coupling and decoupling. But for now I don't see all the possible situations (that are guaranteed to happen in real-life) that make us allow min_transfer_time for transfer_type=5. So I'm afraid that I might forget one and end up restricting the spec.

That's why I am okay with keeping it for now (as optional) just because I don't want to prematurely forbid it. I know that for cases 3 and 4 there's absolutely no possibility for changing the vehicle (because the transfer is either impossible or in-seat) so there's no min_transfer_time to bound that transfer with.

@felixguendling felixguendling Nov 5, 2026

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I guess the only reason to add it is to describe a minimum theoretical time it takes to do the coupling and decoupling.

That's an operational process and not rider-facing though? What implications do you see from "coupling / decoupling takes at least N minutes" to "which connections should be shown to the user"? Anyhow, it's currently completely undefined what min_transfer_time means for transfer_type=5, so forbidding it can only improve the situation.

What might be more interesting: how long does a trip wait for a timed transfer?

The departing vehicle is expected to wait for the arriving one and leave sufficient time for a rider to transfer between routes.

In case of a delay the connecting trip won't wait forever but knowing how long it will wait helps riders make decisions in case of disruptions. But probably this would require another column to not create confusion.

@skalexch skalexch Nov 5, 2026 •
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@felixguendling you're right for the first one. I think if we take both your points together, we probably need another column for "the vehicle waits N minutes". Because min_transfer_time does not point to that whatsoever.

Also, from the definition of min_transfer_time, it says "The min_transfer_time should be sufficient to permit a typical rider to move between the two stops, including buffer time to allow for schedule variance on each route." So not applicable for type 5. I think I'm going to stop the vote, add type 5 and restart after a while.

cc @jfabi


#### Linked trips

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