Traffic signals were first tested in Seattle in 1924, through a collaboration between the Street Department and the police traffic division. The first automatic traffic signal was installed at Fourth Avenue South and Jackson Street for motorists to determine whether the automatic method was better than traffic control by an officer stationed in the center of the intersection.

This graphic by the Seattle Post-Intelligencer art department shows a variety of automatic traffic signals.

Caption information source: The Seattle Daily Times, April 20, 1924, page 8
Caption information also derived from captions written by Post-Intelligencer staff and attached to the back of the photograph