Between the two largest metropolitan areas in Arizona, near a town named Eloy, lies a dangerous stretch of I-10 where the Arizona Department of Transportation is taking action to protect drivers.

“We looked at the whole stretch between Phoenix and Tucson, and it was within this 10-mile section that there was a concentration of crashes, and this is an area that we have, over time, found is especially prone to dust storms,” explained Garin Groff, public information officer for ADOT. “This area, in particular, does have some loose soils and very fine dust. Storms are of particular concern during the monsoon season, which is our summer rain and storm season, primarily active in July, August and September. When these storms are generated, typically in the afternoon and evening, they create this huge outflow of wind that can easily pick up and carry a lot of dust.”

The dust walls reach up to a mile high and tens of miles long, reducing visibility to almost zero.

“For people who haven’t been in one of these storms, it can be difficult to imagine,” Groff said. “It looks like a photo of something from the Dust Bowl era, with this gigantic almost endless wall of billowing dust on the march. Once you’re in it, there are times when you can barely see anything. It can be almost like the sun has instantly set. It’s pretty intense just to be at your house and watch it roll over you, and it’s certainly more intense if you’re on the highway.”

ADOT has maintained a campaign for several years — “Pull Aside, Stay Alive” — with tips for drivers on how to manage dust storms while driving. As the name suggests, the agency urges drivers to delay travel if they see a dust storm coming or get off the highway and wait it out. The worst of the storm usually passes in 15 minutes, Groff said.

Still, there are situations where dust storms come and drivers can’t pull aside, for whatever reason. Crashes still occur, and ADOT has developed a technology it hopes will create additional protection for drivers.

“To our knowledge, it is the first of its kind anywhere, but one of the advantages is all of the technology is existing off the shelf — but we’ve put it together in a way no one ever has before.”

As drivers are on this section of highway, they’ll see a large sign as they approach that says, “Variable Speed Limit Corridor.” After that, there are a series of electronic speed signs 1,000 feet apart. They are typically set to 75mph, which is the existing speed limit. When blowing dust is detected, speed limits are dropped to as low as 35 mph, with each sign reducing limits by 10 mph at a time incrementally.

“We want drivers to have extra breaking time because they can see such a limited distance (during dust storms) that if there is a crash or an object on the road, the slower speed gives them the reaction time to avoid another crash that they might not have been able to react to if they were going 75 miles per hour,” Groff said.

Thirteen visibility detectors along the corridor are constantly checking visibility, and when needed, they automatically trigger activation of the system. Every 2 miles within the corridor, speed limit signs allow for the gradual change in speed limit. Sensors in the pavement indicate that drivers are slowing down.

The system was funded in part by a $52 million federal fast lane grant received by ADOT to widen a section of I-10 in the area from two to three lanes in each direction. As widening was taking place, the dust detection warning system was added. The system cost $6.5 million of the total cost.

The dust detection warning system has been in place since June 2020, but last year’s monsoon season was “a dud,” Groff said. This year, the monsoon season has been more active, but there’s been more rain and less dust.

“It is working as designed. It is detecting dust in the area and activating when it’s there, and we are seeing that drivers are reducing their speed, and that’s the whole objective — to get people to slow down when there is limited visibility so they can stop if they need to.”

The variable speed limits are also enforceable. Drivers can get a citation if they do not reduce speed when the signs are activated. “One of the messages that we share with the public is that the technology does not replace common sense,” Groff said. “Drivers do need to reduce their speed limit when visibility is reduced by dust storms.”