The problem
Existing signals flipped straight from stop to go. Anything already in the intersection — a car, a horse, a pedestrian — had no protected moment to clear.
The innovation
A T-shaped signal with a third, intermediate all-stop position that halted traffic in every direction before the change.
How it worked
A hand-cranked or motorised arm cycles through three states rather than two, inserting a clearance interval.
Why it mattered
General Electric acquired the rights; the clearance interval became standard practice.
The legacy
The amber light is that interval, now automated, at essentially every signalised intersection on earth.
You use this today
The yellow light on your commute.
Sources
US Patent 1,475,024
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