Interstate 19 runs south from Tucson to Nogales, Arizona. It’s relatively short for a two-digit Interstate; I-19 is slightly over 63 miles long, or more specifically, I-19 in 102 kilometers long.

That’s right, 102 kilometers.

The majority of distance based road signs on Interstate 19 are in metric. Speed Limits are displayed in customary Imperial measurements. Many think I-19 has metric road signs because it goes to Mexico.

Not quite.

The majority of Interstate 19 was built and signed around 1980. This is when the United States was going to finally catch up with the rest of the world and switch to the metric system. Arizona, being proactive at the time, decided to sign I-19 with metric signs. Interstate 88 in New York State almost met the same fate, and for a long time had blank exit number panels because they hadn’t decided whether the numbers were going to be sequential, mileage based, or kilometer based. New York State decided to go with the vastly outdated and not helpful sequentially numbered system.

All of this metric versus Imperial discussion took place around the same time I was in elementary school learning units of measure and distance. Since we were going to be metric by 1980, we learned liters, meters, etc. Was the push to metric a Carter Administration thing? I don’t remember a lot about President Carter, other than we suddenly had peanuts with every lunch meal, he had feathered hair, and the Iranian Hostage Situation. As far as Imperial versus metric goes, to this day I cannot remember how many quarts are in a pound or how many pints are in an acre. It makes me husband crazy when I say, “how many pints are in a gallon”? Metric has always made sense to me and it’s a shame the United States never made the conversion. Who cares how many chains are in a teaspoon.

The signs on Interstate 19 were replaced in the late 1990s, again with metric designations, and many have been recently replaced again. While Arizona was going to switch the freeway to Imperial units, after all, while metrification is long overdue, it’s also a kilometers long long-shot, but at the last minute decided to keep the metric signs. There are a few signs that were converted from 2 km to 1 1/2 miles on the northern end at Tucson, but for the most part, I-19 remains a metric highway.

I can’t wait to drive it again! Metrically.