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Other developments important to the future of highways and highway travel were taking place in rapid-fire order. Edward N. Hines of the Wayne County Road Commission invented the center line in 1911 to separate traffic moving in opposite directions. It has been called the most important traffic safety device ever conceived. Michigan won credit in 1917 for painting the first center line on a state highway—the Marquette-to-Negaunee Road. The first stop sign went up in Detroit in the same year and the nation's first "crow's nest" traffic signal tower was built on Woodward Avenue in De­troit, giving police officers a high vantage point for traffic control. The red-yellow-green traffic light was conceived by Detroit police officer William Potts.

World War I brought a new type of maintenance service—snow re­moval. It resulted from the need for all-weather roads to bring materials to the war plants and ship the finished products to railroads and embarkation points. Michigan, in the winter of 1918, kept roadways clear on 590 miles of strategic highways.

In the same year, road officials of the counties banded together to form the Michigan Association of Road Com­missioners and Engineers, later to become the County Road Association of Michigan. The roads under their jurisdiction formed the great bulk of the total mileage in Michigan.