During car accidents, occupants not wearing seat belts will fly around the vehicle, hitting their heads or colliding with other car parts. Seat belts can prevent severe and fatal injuries by distributing crash forces across the more substantial parts of the body – the rib cage and shoulders. They also prevent ejection from the vehicle, associated with high death rates.
Lap Belts
Restraints around the waist and across the chest are called lap belts or two-point seat belt straps. The lap belt partially absorbs a crash’s impact force, preventing you from being thrown (ejected) through windshields or car doors. It is crucial during frontal crashes when you’re most likely killed or seriously injured.
However, seat belts can also cause injuries when they restrain you incorrectly or are defective. Defective buckles may fail to engage properly during a crash, leading to the belt slipping off or failing to retract. Belts with faulty tension detectors can also malfunction, removing the belt’s slack and creating a shearing effect during a collision.
Despite these issues, lap belts are still effective in reducing deaths for backseat occupants in rear-impact crashes. They’re 63 percent effective in vehicles without airbags and 73 percent in cars equipped. They’re also very effective for preventing back seat ejections, which are the leading cause of frontal crash fatalities among unrestrained passenger vehicle occupants.
On rare occasions, lap belts can create vascular injuries when they shear the aorta in the chest during very high-speed collisions. Other serious internal injuries typically accompany these aortic injuries. Sternal fractures affecting the rib cage are another typical seat belt-related injury.
Shoulder Belts
While lap belts restrain your hips, shoulder belts also help keep you from being ejected from the vehicle during crashes. People thrown from cars are 25 times more likely to die than those who remain in their seats, and even moderate injuries can be fatal for adults and children. When front-seat occupants wear shoulder belts, they can cut their risk of death in a car crash by 45 percent and their risk of serious injury by half.
Shoulder belts distribute impact force over a larger area, preventing head injury and minimizing neck motion that causes whiplash. These safety belts can save your life, but if you don’t use them correctly, they can do more harm than good.
Many people don’t use shoulder belts because they feel they’re inconvenient. They can be stiffer to adjust than lap belts, so people may only use them when driving or a passenger in the back seat. But the most common reason for not using a safety belt is that people don’t believe they’ll be saved from a bad accident. Studies show that if you survive an accident without a seatbelt, you’ll spend three to five times more time in the hospital and incur two to seven times more medical costs than those wearing seat belts.
Head Restraints
Head restraints are designed to hold the occupant’s head up and back during a rear impact, protecting the neck and spine. The jolt from such a collision can cause whiplash, a painful condition that affects the ligaments and muscles in the neck and shoulders. It is mainly caused by rear-end accidents and can be painful and debilitating.
In a recent study by IIHS, head restraints were tied with airbags for being the most crucial safety feature in vehicles. More people reported that they would only buy a car with these features rather than just one of them. The research was based on responses from 1,314 surveyed automobile buyers and owners.
The research found that a well-designed head restraint reduces neck injuries by 43%. It is believed that this is because the head restraint prevents the occupant’s head from hitting the seat back hard, which could be very painful.
In FMVSS 202a, NHTSA has proposed to raise the minimum height for head restraints. The agency has also proposed a new test procedure, which it calls an “effective energy absorption” requirement, to replace the existing impact tests for head restraints. It would involve a test using an impactor that moves the head restraint into contact with an inflated head form, similar to how the ECE 25 test is conducted.
Belt Straps
During a car accident, the most common way people become seriously injured or even die is by being ejected from their vehicle. Wearing a seat belt can prevent severe injuries such as broken bones, brain injuries, paralysis, and wrongful death.
In addition to preventing ejection from the vehicle, seat belts can also prevent severe vascular injuries. The shoulder strap in a seat belt controls chest deceleration and keeps it from causing thoracic aortic tears (rips in the body’s largest artery). However, some drivers experience vascular injuries resulting from the force of the seat belts, including bruising on the abdomen or sternum.
Seat belts are designed to ensure the most substantial body parts, like the ribcage and back, take the brunt of the impact. It can lead to bruising and other damage, but these are typically less severe than the damages that would have occurred without the seatbelts.
The webbing used to secure seat belts is called seatbelt webbing. It is different from regular polyester webbing used for ratchet straps and cam buckles, as it is typically thinner and has a lower tensile strength. However, seatbelt webbing is highly versatile and is often used for tents, tarps, bag straps, backpacks, camping gear, and other applications that require a durable yet lightweight material.