I-19, America's Only Metric Interstate – Green Valley, Arizona - Atlas Obscura

I-19, America's Only Metric Interstate

After a short-lived attempt to bring America in line with the rest of the world, this road was left in metric. 


For better or worse, the United States remains one of only three countries that have not officially adopted the metric system. America’s refusal to adopt the metric system has not been for lack of trying, however.

In 1975, Congress passed the Metric Conversion Act, which declared metric as the preferred system of the United States. The U.S. Metric Board was created to implement this conversion. In keeping with this plan, road signs on Interstate 19, connecting Tucson, Arizona, to Nogales, Mexico, were changed so that distances were posted in kilometers. It remains to this day the only highway in America with distances posted solely in kilometers.

As might be expected, a number of motorists have been confused by the unique distances on the signs, and measures have been taken to replace the metric signs with ones with distances displayed in standard American units of measurement. Luckily, the road has been able to maintain its unique identity thanks to the efforts of locals who didn’t want to have to change the signage and directions for their businesses. Presumably they were also dismayed at the thought of losing their singular speedway.

America’s metric experiment proved to be short lived. The Metric Conversion Act and U.S. Metric Board were dismantled only seven years after they were created. Forty years later, America remains committed to its customary system of measurement. However, if you are willing to give an inch and forget about miles, head to Interstate 19 and see what it is like to drive a few kilometers.

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