Every year car accidents claim a staggering 1.3 million lives around the world, with over 3,000 people losing their lives on the roads every day. While the combination of improved car safety features, effective policing of roads and public awareness campaigns can be effective in reducing the road toll, they cannot compensate for the simple reality that cars are hard and the human body is fragile.
Considering what happens to the human body in a car accident is not a trivial exercise. A surprisingly large number of severe car accident injuries happen at speeds that most people would not consider dangerous, and this is in part driven by dangerous driving behaviours rising from lack of awareness of what can happen to the human body in the most common types of car accidents.
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When you are travelling in a car your body and the car have a certain amount of kinetic energy created by the car’s motion. In normal driving situations that energy is gradually transferred to the brakes when the car comes to a stop, usually in the form of heat. In a typical car accident, there is no gradual release of energy, and instead that energy is released in one sudden burst by an impact.
Modern cars are designed to absorb as much of that energy as possible by deforming crumple zones around the car. However, in most situations the car will not be able to absorb all of the energy from the impact. This impact is then transferred to the car occupants, and the human body will then typically be forced into motion and will impact the seatbelt or another part of the car.
The poorer the car build and/or the faster the car is going, the greater the magnitude of these impact energies is going to be, and the harsher the consequences will be for the car’s occupants.
In frontal impacts the human body continues travelling forward after the impact. The body’s kinetic energy will then be dissipated through contact with another part of the car, whether it’s the seatbelt and airbags, which are designed to make this transfer of energy relatively gradual, or the dashboard, windscreen or steering wheel, which aren’t.
If you are wearing a seatbelt in a frontal impact the majority of the force of the impact will be transferred to the meeting between your body and your seatbelt.
While the seatbelt is designed to save your life in a car accident, it may injure you to do so. In a typical frontal impact the seatbelt absorbs a considerable amount of energy as your body collides with it. The harder the impact the more force the seatbelt exerts on your upper torso. This leads to a couple of common injuries, including:
- broken or fractured collarbones where the seatbelt crosses over the shoulder
- broken ribs, particularly in higher speed impacts
- in very powerful impacts all the ribs can break, forcing the ribcage onto the lungs
- if the chest cavity is punctured by a broken rib, then the lungs will stop inflating as the chest expands, a condition which is commonly referred to as a collapsed lung
- if a seatbelt is worn incorrectly, and the majority of the accident force is transferred via the seatbelt into areas of the abdomen not protected by the ribcage, massive internal injuries can take place.
An airbag is deployed with considerable force at the point of impact, and is designed to push your body and head backward, while also immediately beginning a process of gradual deflation to absorb as much of the force of the impact with your body as possible.
However, an airbag can cause injuries of its own. Typical injuries from airbags include:
- temporary or permanent blindness if the airbag impacts the eye area
- facial injuries, including abrasions, burns and broken facial bones
- injuries to the chest, most typically broken ribs
- neck and spinal injuries caused by the airbag snapping the head backwards.
So far we have only considered what will happen if car safety features deploy appropriately in a frontal impact. This is a best case scenario. During high speed impacts, and depending on the car’s build quality, parts of the front of the vehicle may collapse inwards or be forced into the vehicle’s cabin, striking the occupants in the front seats, even when restrained by seatbelts.
This can result in:
- crushing injuries
- broken bones
Failure to wear a seatbelt
Where a car occupant is not wearing a seatbelt in a frontal collision, the body will continue to travel forwards until its kinetic energy is transferred in an impact with another object. What this means in practice is the body will typically collide with the dashboard, steering wheel and/or windscreen. In most scenarios the body will hit the steering wheel before the head hits the windscreen.
The transfer of energy in this collision will be abrupt and typically cause life threatening injuries or death. It is not unusual for the body to be ejected through the windscreen.
Rear end collisions
Rear-end collisions are the most common accident type on Australian roads, and are caused by drivers observing inappropriate following distances. These accidents do not make a major contribution to the Australian road toll. However, they do send tens of thousands of people to casualty wards every year, predominantly with neck injuries.
Occupants of the car being struck
In a rear end collision the occupants of the vehicle being struck experience the transfer of energy as being abruptly forced backwards. In most cases the car seat will absorb much of the energy of the impact as the body is forced backwards. Unfortunately one of the most vulnerable body parts remains exposed in this scenario, as the head will typically snap backwards at great force.
Needless to say this causes a variety of injuries to the back and neck including:
- tearing of spinal ligaments, tendons or muscles
- disc herniation, where the padding between neck or back vertebra are squeezed out of their protective sheathes and onto the spinal chord
- fractures of the cervical vertebra, commonly called a broken neck
- fractures of the back vertebra, which can result in paralysis
- concussion or traumatic brain injury, caused by the impact of the head with the headrest.
Rear end collisions with heavy vehicles
Where the vehicle colliding from the rear impacts a heavy vehicle with high ground clearance, such as a truck, these accidents can be deadly at low speeds.
This is because the car impacting from the rear can slide into the space between the road and the leading vehicle’s chassis, leaving only the car’s windscreen columns to protect its occupants. These are not designed to do this, and will usually be sheared off, leaving car occupants heads and upper bodies exposed to direct impact with the heavy vehicle’s chassis.
Side collisions, such as T-bone collisions, can be lethal at even low speeds. The reasons for this are simple. When a vehicle impacts you from the side, your car doors and their supporting columns are the only parts of the car’s structure available to absorb the force of the impact and prevent the other car from intruding into the cabin.
The ability of these structures to absorb an impact and prevent the cabin being crushed inwards is relatively limited, which means even low speed side impacts can result in:
- crushing of the occupant on the side of the impact, with severe injuries to the thorax, pelvis and upper body. The forces here will typically be strong enough to cause damage to internal organs, as well as breaking bones
- neck and spinal injuries to the occupants on the other side of the car, whose heads and necks will be suddenly whipped in the direction of the impact without any side head restraint to arrest this motion
- head injuries to occupants on both sides of the car, created by the sudden sideways motion of the head at the moment of impact and again as the vehicle comes to a stop. These will be particularly severe if there are no side or curtain airbags to prevent their heads from striking a window or window column.
While rollover accidents are not as common as other kinds of accidents, a far higher proportion of them are fatal. This type of accident bypasses the majority of a car’s safety features, and even your seatbelt may not keep you in your seat during a rollover. In addition few cars are equipped rollover bars that will prevent the car’s roof collapsing inwards onto the car occupants.
During a rollover accident the motion of the vehicle is also likely to cause multiple impacts between the body and other parts of the car as well as airborne debris. Occupants may be ejected from the vehicle entirely by the force of the accident.
It is therefore unsurprising to find that rollover accidents cause a wide variety of serious injuries, including:
- severe head injuries created by multiple impacts of the head with the roof, windows and window support columns, other parts of the car interior and the road surface itself
- severe neck and spinal injuries caused by the whipping motion of the neck as it responds to the car rolling
- broken bones and internal injuries
- severe cuts or dismemberment caused by pieces of torn metal.
Even where a car accident does not lead to injuries sustained from impact with other parts of the car, or from crushing or cuts, the sudden immense acceleration or deceleration generated by a sudden impact can still cause serious internal injuries.
This is because of the way the human body is put together. Delicate internal organs, including the brain, effectively float inside their respective cavities in the human body. During a car accident these organs will maintain, or suddenly gather, momentum until the rest of the body comes to an abrupt stop and they collide with the interior of the body cavity.
Therefore even where a person is restrained and suffers no external injuries in an accident, the following can easily occur:
- rupturing of internal organs, including the spleen and stomach, which can lead to digestive juices flooding the body cavity
- burst veins, which can be particularly dangerous in the brain
- traumatic brain injury created by the collision of the brain with the skull.
These types of injuries may not be immediately apparent after an accident, and it is not unusual for accident survivors to return home from the accident scene only to succumb to their injuries shortly afterwards. This is why it is always a good idea to go to a hospital for a check-up in the aftermath of a car accident, even if you have no severe external injuries.
Believe it or not, it gets worse.
Car accidents can easily result in your vehicle catching alight if the accident causes a fuel leak, a car’s battery ruptures, or if the accident generates sparks or extreme heat from friction. In such situations a spark or electrical impulse can lead to the vehicles involved catching alight. Where the accident was severe enough to trap car occupants or knock them unconscious, there is a significant risk of perishing in the subsequent fire.
Long term consequences
Survivors of even minor car accidents can be left with niggling injuries that can plague them for years. Survivors of serious accidents can suffer severe health and physical consequences for the remainder of their lives, including:
- permanent scarring or deformities
- permanent damage to their brains and cognitive capacities
- partial or total paralysis
- amputation of limbs
- reduced function of one or more limbs or senses.
Even if you survive a car accident in a relatively good state of health, the impact of a serious accident on your life can be devastating. Car crash survivors can experience post traumatic stress disorder (PTSD) or survivor’s guilt, which can impact their behaviour and mental health in a number of ways – and can take years to resolve.
What this means for you
The best way to avoid involvement in a serious car accident is to:
- buy your car with safety in mind, looking out for cars with high ANCAP ratings and advanced safety features
- drive carefully, avoiding reckless cornering and acceleration, mobile phone distraction, tailgating and driving while fatigued or driving under the influence
- learn to drive defensively and develop awareness of other drivers in the road to be able to spot and avoid potential accidents before they happen.
Most importantly, do not speed. The energy generated in a car crash is proportional to the square of the speed the vehicle is travelling at during impact. Therefore, small increases in car speed translate into disproportionally large increases in accident severity at that speed. In turn, speed reductions result in a disproportionate decreases in accident severity.