District of Columbia vs Maryland

The District and Maryland are nearly identical on car seats, and the difference comes down to one technical point. Both require a child under 2 to ride rear-facing, and both keep a child in a car seat or booster until age 8. The District edges ahead because its booster rule has no 4 feet 9 inch shortcut: a child stays in a booster until the eighth birthday regardless of height. Maryland lets a child move to a seat belt at age 8 or once they reach 4 feet 9 inches, so a tall child can graduate a little sooner there. Maryland's own advantages are a forward-facing stage written into the law and a fixed fine. It is close enough that reasonable people could call it a wash, but on the booster the District is the more cautious of the two.

Both require a child under 2 to ride rear-facing. The District's rule (D.C. Code § 50-1703) requires a rear-facing seat for a child under 2 unless the child is both 40 pounds and 40 inches; Maryland requires rear-facing until age 2 until the seat's limit. So a parent cannot legally turn a toddler forward before the second birthday in either place. Pediatricians recommend rear-facing as long as the seat allows in both.

This is the deciding difference. Both jurisdictions keep a child in a car seat or booster until age 8. Maryland releases a child at age 8 or once they reach 4 feet 9 inches, whichever comes first, while the District goes purely by age 8. For a child who reaches 4 feet 9 inches early, Maryland allows the seat belt sooner; the District keeps them in a booster until they turn 8. Because 4 feet 9 inches is the height at which a belt actually fits, the District's age-only rule is the more cautious of the two on this point.

Maryland's edges are that it writes a forward-facing stage into the law and sets a $50 fine for a violation, where the District does not fix a single dollar figure in the same way. Neither requires the back seat. The law that applies is the law of the jurisdiction you are driving in, and since the two line up so closely, a family crossing back and forth can stay covered nearly anywhere by defaulting to whichever rule is tighter: rear-facing under 2 (required in both) and a booster until age 8 (required in both, with no height shortcut in the District).