Arizona vs Colorado

Arizona and Colorado were closer a couple of years ago, but a Colorado law effective January 1, 2025 moved it to the front of the pack and opened a wide gap. Colorado now requires rear-facing until age 2, a forward-facing seat after that, a car seat or booster through age 8, and the back seat through age 8, with the seat belt allowed only from age 9. Arizona sets no rear-facing age, no back-seat rule, and releases a child from the booster at age 8 or 4 feet 9 inches. Colorado is stricter at every stage that changes what restraint a child needs, from the first rear-facing requirement Arizona lacks to a booster and back-seat rule that run a year longer.

Colorado requires a child under 2 who weighs less than 40 pounds to ride rear-facing, and it requires every child under 9 to ride in the back seat where one is available. Arizona requires neither. A Colorado parent can be cited for turning a young toddler forward or seating a 7-year-old up front, while an Arizona parent cannot. These two rules, rear-facing under 2 and the back seat through age 8, are the heart of Colorado's tougher law and the places an Arizona family will notice the change most after crossing the line.

Colorado keeps a child in a car seat or booster through age 8 and does not allow a seat belt until age 9, using age rather than a 4 feet 9 inch shortcut. Arizona releases a child at age 8 or once they reach 4 feet 9 inches, so a tall child can graduate a little earlier in Arizona. The practical effect is that an 8-year-old still rides in a booster in Colorado but may be done in Arizona. Arizona's one advantage on paper is its stated $50 fine; Colorado treats a violation as a class B traffic infraction with the amount set by the state penalty schedule.

The law that applies is the law of the state you are physically driving in. Arizona and Colorado meet at the Four Corners, with US 160 and US 491 connecting the two through the high desert. To stay legal across the whole trip, follow Colorado's stricter rules: rear-face under 2, keep a child in a booster through age 8, and seat every child under 9 in the back. A family moving from Arizona to Colorado picks up a rear-facing requirement, a back-seat mandate, and a booster that runs to age 9, one of the larger jumps in the Mountain West.