If you’re driving on I-10 near Picacho Peak — between Phoenix and Tucson — you may notice speed limit signs that look a little different than normal. These variable speed limit signs are part of ADOT’s dust detection system that runs between Eloy and Picacho Peak. When visibility sensors along the highway detect a certain level of dust in the air, the variable speed limit signs will automatically drop the speed limit from 75 mph to as low as 35 mph. If you encounter a dust storm, do not drive in