The Dynamics of a Rear-End Collision

You might be a cautious driver who always follows the traffic laws and keeps your attention focused on the road so that you can spot potential hazards and avoid them. However, there is little that you can do to prevent another motorist from striking your vehicle from the rear. Unfortunately, rear-end collisions are common and often happen unexpectedly. The National Highway Traffic Safety Administration reports that rear-end collisions are the most common types of motor vehicle accidents and account for 29% of all collisions that occur.

The fact that rear-end crashes are common doesn’t mean that they can’t be serious. Many rear-end collisions cause serious injuries to the occupants traveling in the vehicles that are struck from behind. Both passengers and drivers involved in these types of crashes frequently suffer back or neck injuries. In severe rear-end collisions, they might suffer traumatic brain injuries, spinal cord injuries, and other serious injuries.

Part of the reason why the occupants can sustain serious injuries when their vehicle is struck from the rear has to do with basic laws of physics and motion. Here’s a look at the dynamics of a rear-end collision and the types of injuries people can suffer.

What Happens in Rear-End Collisions?

To understand the dynamics of a rear-end crash, it’s important to understand Newton’s Laws of Motion. These laws are not as complex as you might think, and they apply to everyday situations involving the movement of objects, including your car.

Newton’s first law states that all objects that are at rest or in uniform motion will remain so unless an external force acts upon them. The second law looks at the relationship between the mass of an object, its acceleration, and its applied force, describing the relationship in a simple formula: F = (m)(a). Under this law, both acceleration and force are understood to have a direction and magnitude. Under Newton’s third law, all actions have opposite and equal reactions. In other words, if one object exerts an external force on a second object, the second object will exert a force against the first object that is of the same magnitude but in the opposite direction.

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These three laws are at play in rear-end crashes. To understand what occurs at the point of impact, it is first necessary to understand what occurs before the accident. The occupants of both vehicles are traveling at the same speeds as their respective vehicles under Newton’s first law. For example, if the front vehicle is traveling at 35 mph, so are the occupants’ bodies. If the rear vehicle is traveling at 50 mph, so are the occupants of that vehicle. The uniform motion of the occupants’ bodies will continue until an external force causes them to change direction or stop.

When the rear vehicle strikes the front vehicle from behind, it is the external force that causes a change in the occupants’ uniform motion. When the impact occurs, the occupants of the front car will be thrown forward because of the physical force of the impact, and they might contact the interior surfaces of the vehicle as a result. The force with which the occupants contact the surfaces can be described by Newton’s second law or F = (m)(a). This means you can determine the force of the impact by taking the product of the mass times the acceleration.

When the impact occurs during a rear-end collision, everything inside of the front vehicle will be thrown forward. Since the two vehicles will experience forces that are opposite in direction but equal in magnitude, the occupants in the rear vehicle will experience the physical forces released by the impact with the front vehicle coming back in the opposite direction. After being thrown forward, the occupants in the front vehicle will return violently backward towards the point of impact. This violent back-and-forth movement can cause serious injuries. Since both vehicles involved in rear-end collisions are traveling in the same direction, they will both continue to move in that direction following the collision until they come to a stop.


The National Highway Traffic Safety Administration and the Virginia Tech Transportation Institute (VTTI) conducted a naturalistic study of rear-end collisions. The VTTI completed a comprehensive study that revealed a number of interesting facts about these types of collisions. The researchers found that most rear-end accidents occur when the front vehicle is either traveling at a slow speed or is stopped. In 81% of the collisions, the front vehicle was fully stopped. The researchers also found that most rear-end accidents occurred when the rear driver was following the front vehicle too closely.

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The VTTI researchers also found that the majority of rear-end accidents happened on level, straight roads during the day. In almost half of the accidents, the rear driver was distracted or inattentive and failed to react to the vehicle slowing or stopping in front. Rear drivers who were talking to passengers, using cell phones, or eating were much likelier to be involved in rear-end collisions than drivers who were paying attention to the road. The researchers found that distracted driving accounted for 90% of the rear-end collisions they looked at in the study.

The NHTSA/VTTI study demonstrates the importance of leaving plenty of space between vehicles and avoiding distracted driving. Unfortunately, however, many drivers engage in distracted driving and follow other vehicles too closely, which can be a dangerous combination.

Injuries in Rear-End Collisions

Rear-end collisions can cause debilitating injuries even at low speeds. Some of the most common types of injuries that can occur in rear-end accidents include the following:

• Neck and back injuries – People might suffer soft tissue injuries in their necks and backs, including damage to the spinal discs between their vertebrae. Disc herniations from a rear-end collision can cause chronic pain, and whiplash injuries to the soft tissues of the neck and upper back are common in rear-end accidents.

• Arm, wrist, and hand injuries – Many people who are struck from behind in rear-end collisions attempt to brace themselves with their arms and hands to prepare for impact. When they do, they might suffer fractures and other injuries to their arms, wrists, and hands.

• Facial injuries – Accident victims might suffer facial injuries, including broken bones and lacerations, caused by the impact of their faces against the interior surfaces of their vehicles or from debris flying about inside of the car.

• Rib, leg, and foot fractures – Some people suffer fractured ribs from seatbelts or airbags during a rear-end crash. If they use their legs and feet to brace themselves, they might also suffer fractures to the bones of their legs or feet.

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• Traumatic brain injuries – People can suffer traumatic brain injuries (TBIs) because of the back-and-forth jolting that can occur during and after the impact. This movement can cause the brain to jostle inside of the skull and impact the skull bones, causing damage. People can also suffer TBIs if they strike their heads on an interior surface of the vehicle such as the steering wheel or dashboard.

• Spinal cord injuries – In severe rear-end collisions, people might suffer vertebral fractures and spinal cord injuries. These types of injuries might leave the victims facing permanent paralysis from the site of the damage and below.

• Whiplash injuries – Whiplash injuries are soft tissue injuries to the upper back and neck caused by the whipping motion that your body undergoes when your vehicle is struck from behind. These types of injuries are very common in rear-end collisions and can cause a reduction in the range of motion, chronic pain, headaches, dizziness, muscle spasms, and more.

Common Causes of Rear-End Collisions

Some of the most common causes of rear-end accidents include the following:

  • Driver distraction
  • Drowsy driving
  • Drunk or impaired driving
  • Following too close
  • Speeding
  • Inattentive driving/daydreaming
  • Unsafe lane changes
  • Aggressive driving
  • Reckless driving

Each of these types of driving behaviors can increase the risk of accidents, including rear-end collisions. Most rear-end collisions could be prevented if drivers exercised reasonable caution while driving and kept their attention focused on the road.

Rear-end accidents are among the most common types of collisions that occur. Because of the way in which the forces are released in a rear-end crash, people can suffer serious injuries. By driving cautiously and following the rules of the road, you might prevent yourself from causing a rear-end accident. If you are involved in a rear-end crash, you should seek medical attention to check for injuries and obtain prompt treatment if needed.

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