Traffic lights are traffic control devices placed at intersections.
They use a standard color-coded light system to tell drivers when it is
safe and legal for them to proceed through the intersection. California
red lights keep drivers safe by reducing the likelihood that two
vehicles will try to go through the intersection at the same time. They
also improve the flow of traffic and help keep pedestrians safe by
providing them a safe interval in which to cross the road.
A cool historical fact: the first traffic light was invented in 1868
in England. A policeman operated the light by hand, until it exploded a
year later, injuring the unfortunate officer. Today, traffic lights no
longer require a human being to operate them. Fortunately, they are
also much less likely to spontaneously combust and harm innocent
Before you were even old enough to get a learner's permit, you
probably knew what each color of light meant: red for stop, green for
go, and yellow for "slow down and prepare to stop." However, depending
on how your parents drove, when you were very young you might have
believed a yellow light meant “Go faster!” Did you ever wonder who
decided which colors to use for traffic lights? The basic color code is
the same across most of the world, and it was derived from the colors
of signal lights used on railroads. In fact, William Potts invented the
first 3 color traffic light (the London light only had 2 colors, red
and green) in 1920 in Detroit using railroad signal lights and wires.
Looking even further back, the convention of using "red" to mean "stop"
and green to mean "go" may have come from naval tradition. Ships had
navigation lights on each side of the vessel: a red light on the port
(left) side of the vessel and a green light on the starboard (right)
side. If two ships were on intersecting courses, the ship on the left
was supposed to give way to the ship on the right. So, the ship that
saw the red light on the other vessel’s left side would know to change
Today, California red lights are placed at busy intersections, where
it would be to dangerous or inefficient to have an uncontrolled
intersection. The California Vehicle Code describes how drivers should
react when faced with a red light:
A driver facing a steady circular red signal alone shall stop at a
marked limit line, but if none, before entering the crosswalk on the
near side of the intersection or, if none, then before entering the
intersection, and shall remain stopped until an indication to proceed
is shown, except as provided in subdivision. (California Vehicle code
However, after you have come to a complete stop, if the way is clear
you can turn right or make a left turn onto a one-way street unless
signs are posted saying otherwise.