Permanent claim record · Detroit, Michigan

William Potts borrowed the amber 'caution' light from railroad signaling; Detroit had 15 signalized intersections by 1921, and the three-color standard went national and global by the mid-1930s.

Verified

Raw value (vault-stripped)

{"tags":["traffic-light","inventions","firsts"],"text":"William Potts borrowed the amber 'caution' light from railroad signaling; Detroit had 15 signalized intersections by 1921, and the three-color standard went national and global by the mid-1930s.","category":"engineering"}

Predicate	trivia.fact
Subject	Detroit, Michigan (place)
As of
Status	Verified
Source	Michigan Pop Culture, Game Shows & Trivia Content Mine — Perplexity Deep Research (March 2026) (trust 6.5/10)
Reference	—
Document hash	pending evidence-pack link
Provenance chain
Claim ID	5d3c62d0-e63c-4630-b8f4-cd681257cc0e