Monday 12th February 1973
Four metric distance road signs, the first in the US, were erected along Interstate 71 in Ohio. They showed the distance in both miles and kilometers between Columbus and Cincinnati, and Columbus and Cleveland. As early as 1790, Thomas Jefferson proposed a decimal measurement system, similar to the metric system. In 1968 a study was ordered by Congress. By 1971, a report recommended a switch to the metric system and established a 10-year target time to accomplish it. This led to a National Metric Conference in 1973, which prompted Ohio to display metric highway signs. The Metric Conversion Act (1975) planned a voluntary conversion to the metric system, which produced little voluntary action. Metrication didn’t get very far, but one highway remains: Arizona’s Interstate 19. Other stretches of road occasionally give directions in kilometers, but I-19—which stretches 63 miles, from Tucson to the Mexican border—is the only highway in the US that does it exclusively, across its entire length.
