The United States remains stubborn by not using the metric system to join the rest of the world. We're only one of three countries that use the imperial measurement system.

We tried to switch, however, in the 1970's. It was a valiant effort, really, but difficult to pound into America's thick skull. That did stop the US from creating highway signs that measured in the metric system, and it still exists today.

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Arizona is Home to the Only Section of Highway to Use the Metric System

Arizona I-19 Road Sign
Google Maps

If you're traveling Arizona's I-19 between Tucson to Nogales, Mexico, you may be confused about seeing the road signs in metric. Luckily, for those who can not convert in their head, the speed limit signs are in miles per hour.

I-19 is 102 kilometers, or 63 miles for most of us, in length and is the seventh-shortest primary interstate in the lower 48 United States. Regardless of its short stature, it's the fastest route from Phoenix to Mexico.

Why is Arizona's I-19 Still Measured Using the Metric System?

Arizona I-90 Sign
Google Maps

In 1975, when Congress decided to switch the US to the metric system, I-19 signs were created using the new "standard."

There have been talks about switching the interstate's measurements to the imperial system, but local businesses fought to keep it the way it is saying they didn't want to change their travel directions.

Arizona Department of Transportation wanted to change the signage saying it's confusing for travelers.


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