Interstate 19, unlike other U.S. interstates, is measured in kilometers. The incremental distance markers on the side of the highway note the number of kilometers from the end of the highway in downtown Nogales, and the exit numbers are based on kilometer distances as well.

Therefore, things can get confusing when state agencies use “milepost” references in reporting events on Interstate 19.

Early last Sunday morning, the Arizona Department of Transportation issued a news release that began: “Interstate 19 northbound is closed at milepost 39.”

Since there are no mileposts on I-19, just kilometer posts, this would suggest that the closure was at kilometer 63 in Green Valley, near Continental Road (Exit 63), since 39 miles equals nearly 63 kilometers.

However, the very next line of the ADOT news release explained that “a serious crash has closed the freeway near Tubac.”

So did that mean the closure was at *kilometer* 39, rather than *milepost* 39?

When we followed up with ADOT for clarification, a spokeswoman sent us the initial alert text the agency had received, which read: “Interstate 19 northbound is closed at milepost 39 (approximately kilometer post 48.22)…” But that just made things more confusing, since 39 miles does not equal 48.22 kilometers.

An email to the Arizona Department of Public Safety explaining that that there was some confusion about the location of the crash, stemming from the fact that I-19 is measured in kilometers and the news releases were mentioning miles, didn’t help.

“I-19 is measured in kilometers,” was the terse response from the DPS public information desk.


After another query, the ADOT spokeswoman sent an additional raw alert text reading: “Crash cleared on I-19 northbound from Tumacacori (32) to Tubac (39).” That certainly made it sound like the crash had been in Santa Cruz County, in the Tubac area.

Except that it wasn’t.

The Green Valley News, acting on information received from the local fire district, accurately reported that the crash had happened between Canoa (Exit 56) and Continental (Exit 63) roads in Green Valley.

Perhaps there’s some need for state agencies such as ADOT and DPS to refer to non-existent “mileposts” on I-19 in their internal discussions. But when communicating with the public, they should leave any reference to miles out of the equation. People who use the interstate receive all of their distance cues in kilometers and understand reference points that way. Plus, the mixed measurements also appear to create confusion for the agencies’ own public relations staff.

(Clark is managing editor of the Nogales International.)

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