Deformation zones and collision forces

Modern cars are designed with crumple zones that absorb energy in a collision and protect the cabin. Understanding the forces at play in an accident is important to realize why speed kills.

Kinetic Energy and Speed

Kinetic energy increases with the square of the speed. This means that a small increase in speed results in a large increase in energy.

A car driving at 60 km/h has four times more energy than a car driving at 30 km/h. All this energy must be absorbed in a collision.

Crumple Zones

The car is divided into three main zones:

• Front crumple zone: the front part of the car crumples and absorbs energy gradually.
• Cabin (safety cell): a rigid structure designed to keep its shape and protect passengers.
• Rear crumple zone: absorbs energy in a rear-end collision.

The crumple zones are designed to extend the collision time, which reduces the forces acting on the people in the car.

Relationship Between Speed and Injury Severity

• At 30 km/h, a pedestrian has a good chance of surviving.
• At 50 km/h, the risk of pedestrian death is eight times higher than at 30 km/h.
• At 70 km/h, the chance of survival for a pedestrian is very small.

Therefore, appropriate speed is especially important in areas with vulnerable road users.

Safety Equipment That Works with Crumple Zones

• Seatbelt: keeps you in your seat so that the crumple zone and airbag can protect you.
• Airbag: slows the head and upper body gradually after the seatbelt has absorbed most of the impact.
• Headrests: prevent neck injury in rear-end collisions.
• ABS and ESC: help you avoid the collision in the first place. See brakes and braking system .

Stopping Distance and Consequences

All the energy from stopping distance determines whether you hit the obstacle and at what speed. Even a small reduction in speed can make the difference between life and death.

Further Reading

• Calculation of stopping distance
• Appropriate speed and hidden hazards
• Brakes and braking system
• Braking technique on different surfaces