Sitting rear-facing is simply the safest way to sit in a car. Research shows that the risk of small children being killed or seriously injured is five times higher for those sitting in forward-facing seats than for those in rear-facing seats. New data demonstrates that in a side-impact crash (the most deadly type of collision) rear-facing kids are 4 times safer than those riding forward facing.

Physics: Adults vs Kids
According to the laws of physics, in a crash you always go towards the point of the impact. Therefore, in a frontal crash, everyone moves toward the front of the car. If you are forward-facing--either in a car-seat or a safety belt--your upper body stops quickly as the chest strap on the car seat or seat belt holds you back. However, your head doesn't stop as quickly, but rather travels all the way forward until your chin touches your chest, and then goes all the way back, in the whiplash motion.

Although you'd feel uncomfortable, as an adult you can physically withstand the whiplash motion. Because the head pulls away from the body so violently, having a smaller head in proportion to body makes the effects of whiplash less severe. An adults head is a small percentage of its body--only 6%.

It's quite different for a newborn baby, whose head is a whopping 25% of its body. This means that if a newborn were forward facing in a frontal crash, their head would pull forward with four times as much force as would an adult's!

Strength and rigidity of ligaments and bones in the spine also contribute to an ability to tolerate the whiplash motion. The bones of an infant's spine are made up of soft, stretchy cartilage, the same thing that makes your ears and nose flexible. The ligaments that connect these cartilagenous bones are also underdeveloped and strechy. Scientists have found that a newborn's spinal column (bones + ligaments) can stretch up to 2 inches, whereas the spinal cord inside can stretch only 1/4 of an inch. If the spinal cord is forced to stretch more than it can, it breaks, leaving the baby paralyzed or worse.

Physics: How rear-facing works in a crash
In a frontal crash, when everyone moves to the point of impact--the front of the car--a rear-facing baby will move in a different way. A rear-facing baby will move into the back of his car seat and will slide gently up the car seat. This allows the back of the car seat to absorb the brunt of the impact and distribute the remaining forces along the child's entire back, which is the strongest part of his body. The most important part: because he sits rear-facing, the child's head, neck, and torso all move together in a straight line. The whiplash motion is avoided totally.

This photo shows two crash tests of properly installed car seats – one rear-facing and the other forward-facing – in a frontal crash. Note that both dummies are properly secured in the car seats (i.e. the harness straps are snug). The rear-facing dummy’s head and back are cradled by the back of the car seat. The forward-facing dummy’s head and neck are thrown forward in the whiplash motion.

Rear-facing seats also protect children better during side-impact crashes (the most deadly types of crashes). In a side-impact, everyone moves toward the impact. A forward-facing adult or child will pivot around their pelvis and turn to the side, leaving their head at risk for hitting the doorframe, window, other hard structures, etc. When a child is rear-facing in a car seat, the car seat itself does the pivoting, allowing the child's body to stay in a straight line. And since his head usually does not extend beyond the sides of the car seat, his head is better protected.