Automotive Academy

Rear-facing not only turns out to be safer for infants, but for people of all ages. In fact, we would all be safer rear-facing in cars, airplanes, trains and elsewhere. Of course, this would not be acceptable to most adults.  

When seating babies, it is best to remain rear-facing to the weight and height limits of the carseat.  Some convertible carseats have 30 or 35 pound rear-facing limits.  In all cases, infants should be rear-facing until they are both one year and twenty pounds at the very minimum.

Usually a child can be moved to a booster when they are too big for a harnessed carseat, and once they are able to sit properly in a seatbelt.  A child should be in some type of booster seat until around 8 years old, unless they are already 4′ 9″ tall.

Fortunately, adults are somewhat better able to withstand the forces on the head and neck in a severe crash when they are front-facing. Babies have very immature bones and connective tissue, and this is especially the case when they are younger than 1 year or under 20 pounds. For that reason, front-facing babies face a particularly serious risk of spinal cord injury in a frontal crash.

Frontal crashes are more frequent, more severe and usually have less ride-down time than rear-end crashes.  In such a frontal crash, it is easy to see why a rear-facing carseat is a better choice.  The entire shell of the carseat cradles the child’s back, neck and head. Some seats even have foam protection in the shell to cushion the child even more. 

The crash forces are spread throughout the large area of the child’s back and head, reducing the pressure during the crash, and keeping the head from snapping backward with respect to the body.  Unlike this rear-facing carseat, a child’s legs and head are not restrained at all if they are turned front-facing.  In a serious frontal crash with a front-facing carseat, the head and legs of the child are thrown forward like a rag doll, and serious forces are put on the child’s spinal cord. 

In a front-facing carseat, only the harness couples the energy to the child’s body.  The smaller area of the harness means more pressure on the child.  In the egg analogy, the egg is much less likely to break if it is caught using the whole padded area of your hand rather than with just a couple bony fingers.

Similarly, for the uncommon rear-end crash, a front-facing carseat may be safer than a rear-facing model.  Still, rear-end crashes are much less common and much less severe than frontal crashes, and it is for that reason we choose to maximize the protection for a frontal crash instead. 

In addition, rear-facing carseats can also provide an added degree of safety in side-impacts.  Rear-facing seats will usually protect the head from being thrown outside the shell of the carseat much better than a front-facing carseat in a frontal offset or side impact.

When your child is sat in the car seat ideally you want the child to be coupled in as tightly as possible to the harness system and car seat, and the car seat as tight as possible to the vehicle with the seatbelt of latch system.

When you do this, the child gains all the benefit of “ride-down time” provided by the crushing frame of the vehicle in a crash.  With a loose installation of any kind, the child gets less ride down time and suffers a more severe crash into the harness system.  The analogy is that a tight installation is like catching an egg when you “give” backward with your hand to prevent it from breaking.

A loose installation will be more like holding your arm and hand rigid when you catch the egg.  The egg will splatter in your hand if you don’t give, much like what happens to the internal organs of a person when they are flung into a loose seatbelt or harness. Vehicle frames, advanced seatbelts and airbags are all designed to help passengers slow down more gradually.

Car seats themselves are not designed provide much ride-down time; their main functions are to prevent ejection and to allow the child to be coupled tightly to the vehicle so the frame can provide the necessary ride-down time.??

Rear-end crashes allow for a lot more ride-down time than frontal crashes, the potential energy in a rear-end crash is usually lower than a frontal crash because the speeds involved are slower. In addition, the two vehicles are not usually moving toward each other like they would be in a frontal crash.  That often means one vehicle is allowed to “give”, and the overall ride-down times for both vehicles are much greater, meaning lower forces on the passengers.

The speed of a vehicle is very important to the energy in a crash, even more important than the weight in the vehicle, when frontal and frontal offset crashes occur they are the most severe as they often happen when both vehicles are traveling at a high speed and in a opposite direction.

Rear and rear offset crashes often happen at lower speeds, and most of these cases are when one vehicle is stopped or nearly stopped, and another vehicle hits it from behind at a low speed.  Other cases of accidents like this are when both vehicles are traveling in the same direction at a similar speed and one is bumped from behind.

So the difference in the speed of the vehicles is usually much slower in a rear end crash, this means the energy in the crash will be much lower and if the energy is low there is less chance of a injury. Ride down time is the time is takes for a person to come to a complete stop in a crash. The total force on the passenger will increase with the weight of the person and the speed they were traveling before the crash. The total force on the passenger decreases as the time it takes to stop increases.

While we have often have no control of the speeds involved in a crash, we can do some things to help increase the time it takes for a passenger to come to a stop.  As mentioned earlier, in a frontal crash the vehicles are often traveling in opposite directions at high speeds.  When they crash, both vehicles stop very suddenly, in a small fraction of a second, and even a small increase in the stopping time can considerably reduce the risk of injury. 

Even with best practice, not all injuries can be prevented. Some crashes are unsurvivable. Still, much of best practice is based on statistics, and how to have the best chance to reduce injuries. Best practice may also be based on crash forces and physics. Both are very important regarding the use of rear facing seats.

Rear-facing seats are a lot safer for babies, as they would face a greater risk of spinal cord injury in a front-facing car-seat during a frontal crash, a rear facing seat may not be as effective in a rear end crash but severe frontal and frontal offset crashes are far more common and severe than rear end crashes.

A few factors govern the physics of crashes as they relate to children in car seats. Obviously, the faster the vehicles are going, the more energy will be in the crash.  Perhaps most important is the length of time passengers have to “ride-down” a crash.   The longer the “ride-down”, the more time your skeleton and organs have to absorb the crash energy.   Longer time means less power is transferred to your body, and less chance of injury.

Frontal and frontal offset crashes are accountable for 72% of severe crashes, side impacts are 24% and rear crashes are only 4%. The odds of being in a fatal frontal crash are far higher than a rear end crash. Rear end crashes are very common when cars are moving at a low speed, and these types of crashes usually result in whiplash injury to adults especially passengers lacking head restraints.