The only metric highway in the whole of America could soon no longer exist

America’s only metric highway might be heading for a major identity change or even completely cease to exist.

Interstate 19 in Arizona is the only US highway where signs show distances in kilometers, not miles – leftover remnants from a failed experiment.

Now, a push to replace those metric markers could erase one of the quirkiest road trips in the country, and people are strangely fond of them.

If it happens, a leftover piece of America’s abandoned metric experiment will officially disappear.

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The only metric highway in America

Interstate 19 is a special American highway for cars that stretches about 63 miles between Tucson and Nogales, right down to the Mexican border.

But if you drive the Arizona highway, you will not see that measurement on the signs.

Instead, the markers are in kilometers, a rare sight in a country famously loyal to miles.

For some locals, it is a fun piece of trivia that gives their region personality, and for others, it’s even a niche attraction.

One Arizona engineer called it something that ‘punches above its weight,’ noting that metric enthusiasts have literally flown in just to drive it… Who even knew metric enthusiasts existed?

The reason the highway is metric goes back to the 1970s, when the US flirted with switching to the metric system. I-19 became part of that experiment, and the kilometer signs stayed even after the rest of the country moved on.

But that little piece of metric history is now at risk.

A quirky piece of history may disappear

The US Transportation Department is considering new signage, driven by a message that American roads should feel ‘unmistakably American’ and have some consistency across the whole country.

That shift, tied to political messaging, could mean I-19 returns to standard mile markers.

Some residents are not happy about it; they think replacing all the signage will be too expensive, while others are more open to the change, saying miles are what they see on their car dashboards and what they are used to.

Drivers interviewed on the highway admitted they struggle with conversion, even when they know the basic maths.

One mile equals about 1.6 kilometers, but in the moment, the mental maths can be difficult to do.

For fans of the metric signs, the issue is bigger than convenience because if the markers switch back to miles, I-19 becomes just another boring old interstate.

For now, the metric highway remains, staying special and important to locals and fans.

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