FA-67324 / Railway interlocking logic / Member archive

Temporary speed restriction over train length: rear clearance · case 04

The train accelerates when its front leaves the restriction while its rear is still inside.

Member previewVariant 4 · 3 implementations · 8 checks per implementation

Case contract

A restriction [from_m, to_m) applies while any part of the train (rear = front - length) is inside it: from <= front and to > rear. The limit is the minimum of the line speed and applicable restrictions. next_m is the start of the nearest restriction ahead of the front (from > front) within sight_m of the front whose speed is below the current limit, else None.

Why this case matters

Interlocking logic decides whether trains may be given authority; a wrong decision at this point either grants unsafe movements or strands traffic.

One recorded failure

Sample boundary fixture

This sample comes from the broken implementation of a controlled reproducer.

Boundary fixture	Actual	Expected	Outcome
regression: rear still inside the restriction	`{"limit": 100, "next_m": null}`	`{"limit": 40, "next_m": null}`	Failed

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