A new law effective January 1st, 2022 requires a slow-moving vehicle to use the right lane. Prior to that slow vehicles could use any lane. Arizona Revised Statute 28-721 B. On all roadways, a person driving a vehicle proceeding at less than the normal speed of traffic at the time and place and under the conditions then existing shall drive the vehicle in the right-hand lane then available for traffic or as close as practicable to the right-hand curb or edge of the roadway, except when overtaking and passing another vehicle proceeding in the same direction or when preparing for a left turn at an intersection or into a private road or driveway.