January 5, 2013 6:16 AM Subscribe
THE PROBLEM OF THE AMBER SIGNAL LIGHT IN TRAFFIC FLOW
posted by twoleftfeet (47 comments total)
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(PDF), published in 1959, is the origin
of the yellow interval duration equation
for traffic lights.
But in China, as of Tuesday, yellow lights are now considered functionally the same as red lights
, prompting outcries in the local media
that it is not only unfair, but actually violates Newton's First Law of Motion
. It also violates the history of traffic lights...
Our system of traffic lights is often attributed to the prolific African-American inventor Garrett Morgan
, but his 1923 patent
didn't include a yellow light. Even before that, concerned policeman William Potts
installed multicolored (red, amber, green) traffic signals at this intersection
in Detroit in 1920, inspired by railroad signals.
The yellow light didn't become standard until the 1935 edition
(page 71) of the Manual on Uniform Traffic Control Devices
(which has its own history
While the precise timing of yellow lights is usually intended to prevent accidents
, it's not unusual for that timing to be adjusted for profit