Kilometer marker on US Interstate Highway

While the US uses miles to mark all of there interstates there is one interstate where the mile markers are actually labeled in kilometers. Interstate 19 in Arizona, between Tucson and the Mexican border, uses kilometers for mile markers and destination signs. Speeds are still posted in miles-per-hour.

The metric signs were installed in the 1980s when it looked like the United States was converting to the metric system. Complete conversion to metric never happened, but most of the signs along this interstate still stand.