Require from_stop_id and to_stop_id in recommended transfer point transfers (empty or 0)

[skalexch]

Summary

In transfers.txt, require from_stop_id and to_stop_id when transfer_type = 0 or is empty (recommended transfer point).

This affected requirement rules, therefore it's a non-functional change. It requires a discussion period, a review period and a vote.

Describe the Problem

In transfers.txt, when transfer_type = 0 or is empty, it means that it is a recommended transfer point between routes, which should include a from_stop_id and to_stop_id.
However, the spec currently only requires from_stop_id and to_stop_id when transfer_type =1, 2 or 3

The issue was raised by a community member in the #gtfs Slack channel (thread): "from_stop_id and to_stop_id are "Required if transfer_type is 1, 2, or 3", but aren't they also required if transfer_type=0 or empty?"

Type of change

GTFS Schedule

• Functional Change
• Non-Functional Change
• Documentation Maintenance

GTFS Realtime

• Specification Change
• Specification Change (Experimental Field)

Proposed Discussion Period

We want to leave the discussion period open until after the holidays to accommodate holiday schedules and to make sure the community has an eye on this. We intend to start a one-week review period and the vote mid-January.

Therefore, we propose a discussion period of 6 weeks (too accommodate the holidays), the discussion period ends on 9 January 2026 at 23:59:59 UTC.

Proposal Update Tracker

Date	Update Description
(2025-12-01)	Raised PR - Started discussion period

Checklist

• I have read and understood the GTFS Change process.
• I have read and understood the GTFS Guiding Principles.
• I understand the Role of Advocate and the Responsibilities attached to it.
• I have signed the Contributor License Agreement (CLA).
• I have ensured that this proposal is not covered by an existing Pull Request.

[skinkie]

Please don't do things like this: Consult the slack thread for more detail.

[skalexch]

@skinkie good point, I updated the description to be clearer.