The Common Causes and Physics of a Car Crash

Every year, there are over 6 million car accidents in the United States alone. While some may be simply “fender benders,” many others result in extensive damage, serious injury and death.  

Understanding what causes most accidents, and furthermore what physical forces are at play in a crash, may help you understand how you can become a safer driver and avoid being a statistic.

Accident Avoidance

The best way to avoid being hurt in a car accident is to not be in one in the first place. If you have taken a driver education course in school, a one-day class to help reduce your insurance costs, or you’ve simply read the news, you are without a doubt familiar with the fact that driving while intoxicated is an extremely dangerous and criminally punishable behavior.  

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Common Causes & Physics of Car Crash Infographic

What Are Some Common Causes Of Traffic Accidents?

Drunk Driving

Drunk DrivingLet’s look again at the facts:

  • Behind distracted driving, (discussed below), drunk driving is the number one cause of most car accidents in the United States and by far the deadliest.
  • More than 25% of all traffic fatalities are the direct result of alcohol impairment.
  • 29 people die and 800 people are injured each day in the United States in car accidents involving a drunk driver.
  • A driver with a blood alcohol level above 0.10 is seven times more likely to be involved in a fatal accident than a sober driver.

The Rolling Right Turn on Red

ROLLING RIGHT TURN ON REDThis common behavior involves a failure to come to a full and complete stop at a red light or stop sign before turning right. Many people fail to follow the law. 

As a driver in this situation, you’ll likely be looking to the left for traffic as your car is still rolling and not see the car, pedestrian, or cyclist in front of you. 

This type of behavior accounts for 6% of all pedestrian fatalities, a shocking 21% of which are children.

Asleep at the Wheel

Asleep at the WheelStudies reveal that drowsy driving causes 6% of all car crashes, and 21% of fatal crashes. What’s more, 37% of people in surveys admit to having fallen asleep while driving at least once in their lives. Scientists say that humans are poor judges of their own sleepiness, and even less aware of “microsleeps,” which are brief intervals during which our brains effectively go ‘offline’ for a few seconds. 

This happens without our conscious awareness. Sleep science tells us that we all need 7 to 9 hours of actual sleep, not just time in bed, each night. Less than that and you shouldn’t be driving. Furthermore, if you’re driving at night and you feel sleepy, it’s time to pull off the road and get some rest.

Losing Control

Losing ControlLoss of vehicle control accounts for 11% of all motor vehicle crashes. We believe that it can’t be us, but a classic study shows half of all drivers rank themselves in the top 20% in terms of driving safety and skill. In short, we all overestimate our abilities as drivers. Race car and test driver Andy Pilgrim has said that most drivers “are not even close to matching the capability of their car, as far as going fast.” 

As such, aggressive maneuvering and taking sharp turns too fast account for 5% of all crashes. Not slowing down for water on the road accounts for 2% of crashes. The other 4% or so of crashes happen when another driver, or a sudden turn, surprises us and instead of reacting calmly, (as we might imagine ourselves doing), we overreact and overcompensate. 

Therefore, it is best to always drive within the speed limit with the expectation that unexpected events will happen.

Driving Blind

Driving BlindAs illustrated in this video, one instance of driving ‘blind’ involves making a left turn at an intersection when there’s a large vehicle blocking your view of oncoming traffic. Another is running a red light in the belief that there won’t be a car crossing your path. And a third example is racing down a road without the awareness that it’s about to end in an intersection. These three types of behavior cause 12% of all crashes. 

The lesson? Always assume another vehicle will be precisely where you’re thinking it won’t.

Rear-end Collision

Rear End CollisionRear-enders account for between 23% and 30% of all crashes. That’s a large number. What causes them? Simple: Following too closely. We’re rushing, believing we’re shaving time off our trip when we barely save 26 seconds per day by hurrying. 

Also, we’re accustomed to thinking that rear-end crashes are usually just harmless fender-benders. But many times, cars twist and flip in unexpected ways, causing chain-reaction collisions and serious injuries, not to mention numerous long-term difficulties.

Distracted Driving

Distracted DrivingTypically, accidents involving distraction involve departure from our driving lane, or the road itself. At least 33% of all accidents are caused by distraction, the single largest cause. Cell phone use while driving is the most common precursor, but distraction can also be caused by billboards, activities within the car, other accidents, or simple mind-wandering

The best way to stay alive is to put away the technology and focus on driving, which is difficult enough. Human beings are terrible at multitasking.

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Car Crash Science

Now that we’ve looked at some of the most common causes of car accidents, it’s time to consider the physics involved when a car does crash. While no two vehicle crashes are ever exactly the same, the physical laws of our universe are always the same. This was discovered, quantified and published by Sir Isaac Newton back in 1687. His formulas are still used today by crash investigators and accident reconstruction specialists. Here’s a brief discussion of his famous three laws of motion.

Newton's First Law

Newton's Law 1 DiagramNewton’s First Law of Motion states that a body in motion will continue moving in the same speed or in the same direction unless or until it is acted upon by an external force.  It also states that an object ‘at rest,’ (that is, not moving), will continue to be at rest until some outside force acts upon it.

When it comes to car accidents, we can imagine a car colliding with a concrete wall. The car was in motion, but the wall caused the car to rapidly decelerate and finally be ‘at rest.’ The passengers in the car, provided they were wearing restraining belts, will also decelerate rapidly as they are attached to the car and share its state of motion. This is good, because if they were not, the passengers would continue moving after the car had stopped. They would not be in the same state of motion as the car.  

In practical terms, they would fly forward through the windshield and be hurled into the air, most likely resulting in their deaths.

Newton's Second Law

Newton's Law 2 DiagramNewton’s Second Law of Motion states that acceleration is produced when a force acts upon a mass. The greater the mass of the object, the more force is required to accelerate that object.  As it relates to car crashes, the impact force of a car on another object is equal to its mass multiplied by its acceleration, of which speed is part of the calculation. 

Put another way, the force of an impact is the total force exerted on an object during a collision.  Therefore, the higher the speed, the higher the impact force of the crash. It also means that the impact force of an object with a lot of mass, say a dump truck, will be larger than that of a small car.

Newton's Third Law

Newton's Law 3 DiagramNewton’s Third Law of Motion states that for every action, there will be an equal and opposite reaction. For example, if a car traveling at 30 miles per hour strikes an immovable wall, the force created by the collision will be equal in magnitude to the force of the car striking the wall, and that force will move backward through the car from the wall.

This explains why a collision at low speeds is less serious than one at high speeds. Newton’s Third Law also explains why, when cars of unequal mass collide, the vehicle with more mass will force the smaller vehicle backwards and the smaller vehicle will experience more impact force.

Two Types Of Collisions

Elastic & Inelastic DiagramWhile there may be an infinite way in which two vehicles can collide, in terms of physics there are only two: elastic and inelastic.

In an elastic collision, two objects collide and then ‘bounce’ apart, such as when a rubber ball strikes another. Almost no energy (also called ‘kinetic energy’) is lost to sound, heat or the deformation of objects.

An example of this type of collision involves your car’s bumper. A car’s bumper works by using this principle to prevent damage. In a low-speed collision, the kinetic energy is small enough that the bumper can deform and then bounce back, transferring all the energy directly back into motion. 

However, car bumpers are also made to collapse if the speed is high enough, and the benefits of an elastic collision are lost. If this is the case, the bumper will crumple and distribute some of the energy of the crash into itself, rather than the car’s occupants.

The other type of collision in physics is an inelastic collision. Here, the objects collide but do not bounce away from each other. Examples would include our previous car driving into an immovable wall, or two cars colliding with each other and coming to a stop.  

In an inelastic collision, the kinetic energy involved is converted into sound, heat and the deformation of objects. Anyone who has witnessed a car accident can attest that it is both loud and causes damage.


Momentum DiagramDefined as “mass in motion,” all moving objects have momentum. The momentum of a moving object is equal to its mass multiplied by its velocity. 

An object has a large momentum if either its mass or its velocity is large. Thus, a fast-moving car has more momentum than a slow-moving car, if they have the same mass. Using the same principle, a heavy truck will have more momentum than a small car even if they are traveling at the same speed.

The important thing to remember here is that the more momentum an object has, the harder it is to stop, and the greater energetic effect it will have if it is brought to a stop by impact or a collision.

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Martin, Harding & Mazzotti, LLP has a wealth of experience in dealing with insurance companies and in protecting your rights to receive the compensation you’re entitled to. We’re here 24 hours a day, 7 days a week.

Vehicle Features That Help In Crashes

Seat Belts

Seat Belt IconAs mentioned above, seat belts are designed to stop vehicle occupants from continuing at the same speed the vehicle was traveling just before the impact. The seat belt allows an occupant to be connected to the whole vehicle, which allows for the momentum of a person’s body to be slowed down at the same speed as the car.

You may think that being attached to the car in a crash is a bad thing, but this is not the case in most crashes. Seatbelts allow an occupant to take advantage of the vehicle’s energy-absorbing design (discussed below). 

The secondary job of a seatbelt is to spread the stopping force of the collision across the sturdier parts of a person’s body in order to minimize injury. Most modern vehicles are equipped with pre-tensioners, which pull inward on the belt in the event of a crash. If the passenger is seated properly in the vehicle, the pre-tensioner forces the person’s body into the best possible crash position.

It should be remembered that, while a seatbelt can restrain a person’s torso effectively (seat belts reduce your chance of dying in an auto accident by at least 45%), it cannot restrain the head. Furthermore, crashes at very high speeds effectively nullify the protections of a seatbelt.


Airbags IconFront and side airbags are designed to help slow and stop vehicle occupants from continuing forward after a crash and being ejected from the vehicle. They also prevent drivers from striking the steering wheel and windshield, and protect other occupants from striking hard surfaces like dashboards and windows.

An airbag can also prevent the occupant’s head from swinging through the full range of motion and damaging the neck.

Both seatbelts and airbags spread out the time that the force of deceleration (from a crash) is applied to a passenger. Deceleration in itself does not cause injury; it is the sudden deceleration over a very short period of time that does. Airbags and other restraining technology minimize injury in all but the highest speed crashes by lengthening the deceleration time.

Crumple Zones

Crumple Zones IconCrumple zones on cars allow the vehicle to absorb some of the initial impact and decrease the force applied to the vehicle occupants.

The crumple zones are located toward the front and rear of a car and, as their name implies, are designed to collapse easily in the event of a collision. Thus, instead of a car coming to an abrupt stop, along with the passengers within the car, the crumple zone absorbs some of the impact force by flattening.

Crumple zones allow the car to decelerate more slowly and spread the energy of the car to other structural components of the car.

A car’s passenger compartment is built much more sturdily and does not collapse around the occupants.  Instead, it redirects energy away from the driver and passengers and reduces injury.

For a stark depiction of how a crumple zone of a modern car works, see this video of a crash test between a modern car and an older car without a crumple zone.

Is Bigger A Vehicle Better Or Safer For An Accident?

Generally speaking, you are more likely to survive a car crash if you’re in a bigger vehicle than the one you’re in a collision with.

Vehicle ComparisonsIf you hit another vehicle traveling at the same opposite angle and speed, the larger, heavier vehicle will have a greater momentum force and, therefore, will cause more damage to the smaller, lighter vehicle. The larger, heavier vehicle may push the smaller, lighter vehicle backward and even crush the smaller vehicle. This is commonly seen in accidents between tractor-trailers and passenger vehicles, where the truck driver walks away unscathed while the passengers in the other vehicle suffer serious injuries or are killed.

According to the National Highway Traffic Safety Administration (NHTSA), an occupant of a passenger vehicle, (such as a sedan), is 3.3 times more likely to be killed in a head-on collision with a “light truck,” (which includes SUV’s, pickups, and vans). So, at least in head-on crashes, the type of vehicle plays a more significant role for occupant safety than does the vehicle’s crash test rating.

However, driving an SUV is not your only option to stay safer on the road. Studies performed by the Insurance Institute for Highway Safety (IIHS) have demonstrated that any additional size and weight of the car you’re driving (versus the one you collide with) can favorably influence the protection of the occupants in the event of a crash.

The IIHS studies also revealed that, in general, occupants in smaller cars are the least protected when there is a crash. The tradeoff for price [JS1] and fuel economy can, in fact, be very significant.

However, the percentage of fatalities in rollover crashes, where there may have been no collision with another car, was highest for SUV’s, at 43%, followed by pickup trucks, (40%), vans, (24%), and passenger cars at 20%.

There are, of course, many factors to consider when selecting a car, such as the number and variety of safety features now offered on modern vehicles. You should also select a car that has performed well in dynamic crash tests, that is, tests that involve more than a single, frontal impact. Rollover testing is an example. For more information on specific vehicles, check the IIHS’s ratings page here.

Can You Survive a 70 mph Crash?

Theoretically, yes, but it very much depends on the type of collision and the safety features of the vehicle.

According to research, the highest speed at which you are likely to survive a head on collision without serious injury is 43 mph, assuming the proper use of safety belts in a well-designed car with crash structures like crumple zones and airbags, (discussed above).

However, the odds of surviving a head-on crash drop exponentially at speeds above the 43-mph mark.

Probability of Casuality GraphIt is essential to note here that the IIHS conducts their frontal crashes, (head on, moderately overlapping and small overlapping), at 40 mph, not at higher speeds. Car manufacturers simply do not design their vehicles to protect occupants at speeds above this, because the kinetic forces involved are just too great.  

So even though the car you’re driving, or considering, has a “5-star” or “Good” frontal crash test rating, this only applies if you’re traveling 40 mph at the time of a frontal collision with a car of similar (or less) weight as yours.

Survival StatisticsThe forces in a collision are quadrupled when the speeds are doubled, because kinetic energy increases with the square of velocity, according to Newton’s formula. This means, practically speaking, a crash at 80 mph carries four times the energy as a crash at 40 mph.

So, if your car has a “good” frontal crash score, and you collide with another vehicle of equal or lesser weight head on at 40 mph, your odds of survival are close to 100%.

But a 70-mph crash involves 306% more kinetic energy than a 40-mph crash.  In crash studies, when a car is in a collision at 300% of the forces it was designed to handle, the odds of survival drop to just 25%.  

Therefore, in a 70-mph head on collision with four occupants in your car, odds are that only one person in the car will survive the crash.  Are you willing to take a chance like that?


As we have seen, there are a number of common crash scenarios that can easily be avoided by reducing speed, eliminating distractions and leaving extra space between you and other cars. We’ve also seen that even though we may think we are excellent drivers, we could all use a (safe) dose of humility when it comes to operating our vehicles. 

Vehicle collisions are all too common, and we hope that by understanding some of the physics involved in a car crash, you will take precautions such as always using your seatbelt and researching safety ratings when making a vehicle purchase. But learning the physics involved should also instill more driving caution in general, given the size, weight and speed capabilities of the vehicles we use every day.

Contact The Experienced Auto Accident Attorneys

If you or anyone you know has been injured in an automobile accident of any kind, the attorneys at Martin, Harding & Mazzotti, LLP have a wealth of experience in dealing with insurance companies and in protecting your rights to receive the compensation you’re entitled to.  

Our attorneys handle all types of motor vehicle accidents, including those involving automobiles, motorcycles and all types of truck accidents, from eighteen-wheelers to delivery vans. Contact us today for a free case evaluation by calling 1-800-LAW-1010 (1-800-529-1010). We’re here 24 hours a day, 7 days a week to take your call, or use our convenient online contact form.

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