Interstate 19 is a highway running from the Tucson, Arizona to the Mexican border. It is unique among American highways: the signs are in metric.
You probably already know that the United States is one of the only countries in the world to still use non-metric measurements for most things. I’ve heard that Liberia and Burma are the other two, which makes an interesting trio. So it’s pounds instead of kilograms, Fahrenheit instead of Celsius, and miles instead of kilometres.
There have been pushes to convert the United States to metric since the 18th century but it has never really taken off, for many reasons (including attacks by pirates! But that will be a future blog post). As a result of one of these pushes, the signs on the I-19 were converted to metres and kilometres, and they’ve mostly stayed that way since.
The US government did attempt to change the signs back to miles, but apparently the local businesses want them kept around – they’re a novelty, and maybe even a bit of a tourist draw. Fair enough.
[Thanks to Shaun T for suggesting this topic]