Kids also tend to put the shoulder belt behind their back or under their arm if it doesn't fit right, another risky move because they won't have upper protection and could rotate out of the belt or hit their heads. While booster seats and seat belts are considered a safe combination, there are several shortcomings, says Joseph Colella, executive director of the DANA Foundation, a safety group he founded after a crash killed his niece even though she was in a car seat. Booster seats must be used with both lap and shoulder belts. Booster seats typically only go up to 60 pounds, and many kids are too short or too young and undeveloped at that weight to have an adult seat belt fit properly. Boosters aren't secured to the vehicle and can slide around, sometimes even tipping over when cars make sharp turns.
Children tend to be fidgety, leaning over in ways that puts the seat belt out of proper position.
There is a lot of freedom to move in a booster seat with a seat belt. From a crash dynamics standpoint, we don't know how much better protection a five-point harness gives than a seat belt, we just know it spreads the forces over a wider area of the body, making better contact with the hips and chest and shoulders. Since 1989, new cars had to be equipped with lap and shoulder belts in the rear side positions. The National Transportation Safety Board, an independent federal panel, has been urging automakers to install shoulder belts in the rear middle position as well because that's widely considered the safest place in the car. In addition, the government announced that a new way to attach child seats to cars would be required in all cars by 2002.