A Unique Choice in Measurement
Interstate 19 (I-19), connecting Nogales at the U.S.-Mexico border to Tucson, Arizona, is the only highway in the United States to use metric measurements for its distance markers and exit signs. Distances are marked in kilometers, a decision tied to a short-lived push for metrication in the 1970s.
Origins of the Metric Signs
When I-19 was completed in 1978, the U.S. government was encouraging a transition to the metric system. Federal funding supported the use of metric signage as an experimental program, making I-19 the only interstate to fully adopt this system.
Local Controversy
The metric system created confusion for drivers unfamiliar with kilometers. Over the years, there have been debates about replacing the signs with standard mile-based markers, but the metric system remains.
A Highway with Distinctive Features
Stretching 101 kilometers (63 miles), I-19 also features bilingual signs in English and Spanish due to its proximity to the border. This distinctive combination makes it one of the most unique roads in the U.S. highway system.
Interstate 19 (I-19), linking Nogales at the U.S.-Mexico border to Tucson, Arizona, is the only U.S. highway using metric measurements for distance and exit signs. Completed in 1978, this unique choice stemmed from a government push for metrication during the 1970s.🧵1/4👇 pic.twitter.com/r4juaKlIPn
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