FA-67868 / Traffic signal timing plans / Member archive

Webster cycle length: the cycle is not capped at the controller maximum · case 03

Webster cycle length returns a wrong result when the cycle is not capped at the controller maximum.

Member previewVariant 3 · 3 implementations · 8 checks per implementation

Case contract

Input {phases: per-phase lists of lane-group flows veh/h, sat: saturation flow per lane group, lost: lost seconds per phase, allred: extra all-red seconds per cycle, cmin, cmax}. Y is the sum over phases of the critical (largest) flow ratio; L = lost*phases + allred. If Y >= 0.9 return 'oversaturated'. Otherwise C0 = (1.5L + 5)/(1 - Y), rounded UP to a multiple of 5 s and clamped to [cmin, cmax]. Return {cycle, lost: L, y_milli: floor(1000Y)}.

Why this case matters

Signal timing arithmetic is exact and integer or rational; a wrong rule silently produces unsafe or inefficient timing plans.

One recorded failure

Sample boundary fixture

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

Boundary fixture	Actual	Expected	Outcome
timing oracle 1	`{"cycle": 60, "lost": 15, "y_milli": 870}`	`{"cycle": 120, "lost": 15, "y_milli": 870}`	Failed

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