In Arizona the maximum speed limit on Interstate Highways is 75 mph (121 km/h). This limit may be applied outside of “urbanized areas”, where speeds of over 85 mph (137 km/h) on any highway (regardless of the posted speed limit) is considered a criminal (rather than civil) offense. The default speed limit of 65 mph (105 km/h) is posted outside of “business or residential” districts and, within those districts, the default speed limit is 25 mph (40 km/h). The school zone speed limit is 15 mph (24 km/h), while some may vary between 25 to 35 mph (40 to 56 km/h). Exceeding these limits only in the best of driving conditions is considered prima facie evidence of speeding. Altered speed limits are not prima facie.
I-10 near the California border is reduced to 65 mph (105 km/h). Some portions of I-15 have the same regulations due to sharp curves. There is an exception of urban highway in Casa Grande, with a speed limit of 75 mph (121 km/h), while other urban highways are capped at 55 or 65 (89 or 105 km/h). Within “business or residential” districts, exceeding the speed limit by more than 20 mph (32 km/h) is considered criminal. Within “urbanized areas”, 55 mph (89 km/h) speed limit citations are given for “waste of a finite resource”. This exception only applies within a 10 mph (16 km/h) threshold. As long as the speed does not exceed 65 mph (105 km/h), the infraction is not recorded as a traffic violation for the purposes of a point system.
Non-passenger vehicles in excess of thirteen tons, or “vehicles drawing a pole trailer” weighing more than 3 tons may not exceed 65 mph (105 km/h) unless signs are posted that allow such a speed. Yet this does not differ from the default speed limit, and has the practical effect of requiring extra consideration for posting a standard speed limit sign in excess of 65 mph (105 km/h). A non-numeric minimum speed limit is incorporated with the basic speed rule in Arizona, which also prohibits speeds higher than would be “reasonable and prudent”.
Night speed limit signs are posted on some roads within Tucson city limits that do not have street lights. Examples: Fort Lowell Road from Oracle Road to Country Club Road, 22nd Street from I-10 to Cherry Avenue.