Why Kilometers Used on I-19?

This article authored by: Rob Hallberg

I was driving on I-19 this weekend and, even though it is no surprise to me, I wondered about the origin of the “Mileage” signs on the route. The “Mileage” signs, as most of you are aware, are actually in Kilometers.

Why were Kilometers used? Are there other US roads that use Kilometers? Will they be changed and used Miles instead?

History: I-19 was completed in 1972, and miles were used for distances. In 1975, Congress passed the Metric Conversion Act, which declared metric as the preferred system in the US. In 1980, the US Metric Board in conjunction with Arizona, awarded a contract to replace all of the distance signs on I-19 with ones using the metric system.

I-19 is the only Interstate highway in the US to use the metric system.  The majority of US citizens were opposed to a change to the metric system, and in1982, the Metric Board was disbanded. The United States, along with Liberia and Myanmar, are the only countries in the world that have not standardized on the metric system.

It is doubtful the signs will be changed to miles although there have been several attempts. Cost (about $1.5 million) is the primary reason, although businesses along I-19 have also complained that it would cause a change in exit numbers which they currently use in advertising.

For those of us confused with these signs, there is one silver lining. Speed Limit signs were NOT changed. At the time the signs were installed, the National Speed Limit was 55mph, so the speed limit would have been posted as 88kph.  At today’s speed limit of 75mph, signs would read 120kph, allowing you to say you “exceeded 100” on I-19.

Rob Hallberg

Rob and Catherine Hallberg are Associate Brokers with Long Realty, a Berkshire-Hathaway Affiliate and Southern Arizona’s largest Brokerage. Send Rob and Catherine an email  for a fast response to your questions; for an even faster response, Call (520) 407-8667.

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