Arizona DOT is using economic-stimulus funds to kill two birds with one stone: “modernize” mile-marker language while bringing the signs up to retroreflectivity standards. Photos: Arizona DOT

How many kilometers equal a mile?

Or better yet, an interstate sign states that your exit is 17 kilometers away. How many miles is that? Judging from your car's speedometer, how long will it take you to get there? If you weren't able to convert the distance and driving time in your head in, say, less than a minute, you may sympathize with the often-times frustrated drivers along Arizona's Interstate 19.

Since 1980, the signs along the 63-mile — or 100-kilometer — stretch of I-19 from Tucson to Nogales have been in metrics. They were a result of a federal experiment with metric conversion in the 1970s and ‘80s, and this stretch of highway just happened to be under construction at the time.

Although the U.S. government's drive to get Americans to think metric ran out of gas within the decade, the metric signs still lingered on the road south of Tucson — much to the dismay of imperial-unit-thinking drivers.

“There were many complaints when we replaced the original signs with the metric system,” says Linda Ritter, public information officer with Arizona DOT (ADOT). “And we continue to receive complaints from motorists who are more familiar with miles than kilometers.”

The most common grievances involve driver confusion. Although speed-limit signs have remained in miles-per-hour to be consistent with speedometers, the exit signs perplex drivers trying to gauge distances and the time it will take to reach destinations.

The cause for that confusion is about to change.

Last month, Arizona's transportation board approved $1.5 million to replace the signs. The funding is part of the federal stimulus package, which provides $521 million to the state for roads and bridges. Considered a “shovel-ready” project, it is being put out for bid this month.

A note to critics who see replacing the metric signs as frivolous stimulus spending: The conversion is not the main reason for new signs; it's just a happy byproduct.

After nearly 30 years of service life, the signs are old. Plus, they don't meet the new federal retroreflectivity requirements (see “Countdown to compliance,” page 28). Because of this, I-19 sign replacement has become a priority for ADOT.

“We're obligated to replace these signs from a highway safety standpoint,” says Ritter. “Since state statutes prohibit us from designing or building anything in metric, we are designing the project using the English system.”

Distance markers, exit numbers, everything — including speed-limit and warning signs — will change. And everything from maps to GPS systems will have to change along with them.

Now local drivers will have a new learning curve: exit numbers.

“The exit numbers were determined in kilometers, so they'll be changing as we convert to miles. However, we'll put the older exit numbers on the signage for one year,” Ritter says.