What is the most important factor in determining how hard a vehicle hits a fixed object?

• A. The weight of the vehicle
• B. The angle of impact
• C. The type of fixed object
• D. The speed on impact

Answer: (D)

Speed at impact is the biggest factor because it determines how much energy the crash must absorb. The energy of a moving vehicle is kinetic energy, which scales with speed squared (and with mass). That means even small increases in speed dramatically raise the energy that has to be dissipated when you hit something fixed. The force you feel depends on how quickly that energy is dumped, which is influenced by how long the collision lasts (crumple zones, barriers, etc.). While the vehicle’s weight, the angle of impact, and the type of fixed object can affect how the energy is distributed and absorbed, they don’t change the starting amount of energy as much as speed does. So going faster makes the hit much harder. Reducing speed near fixed objects is a key safety factor.