In this fact page we will cover:
- Why crashes at higher speeds cause more severe injuries
- The relationship between kinetic energy and force of impact
Every day, road crashes cause devastation to individuals, families and communities across the UK and the globe. Vehicle speed is always a factor in the severity of the incident.
Driving is unpredictable and if something unexpected happens on the road ahead – such as a child stepping out from between parked cars – it is a driver’s speed that will determine whether they can stop in time and, if they can’t stop, how hard they will hit.
A vehicle travelling at 20mph would stop in time to avoid a
child running out three car-lengths in front. The same vehicle
travelling at 25mph would not be able to stop in time, and
would hit the child at 18mph. This is roughly the same impact
as a child falling from an upstairs window.
The greater the impact speed, the greater the chance of death. A pedestrian hit at 30mph has a very significant (one in five) chance of being killed. This rises significantly to a one in three chance if they are hit at 35mph. Even small increases in speed can lead to an increase in impact severity.
Kinetic energy and impact force
When a car crashes, it’s the amount of kinetic energy that the car has which determines the force of impact. Kinetic energy is the energy of motion. Small increases in speed lead to much higher increases in kinetic energy.
When you’re driving, it’s hard to perceive that a slight increase in speed is really so damaging. It’s easy to let speed creep up. But a crash at 30mph involves twice as much energy and destructive potential as a crash at 20mph.
It is in everyone’s best interest for drivers to ensure that their speed is appropriate for the road they are travelling on and does not place them at increased risk of being involved in a crash resulting in death
or serious injury.
- Impact speed and a pedestrian’s risk of severe injury or death, the AAA, 2011
- Davis, A., Essential evidence: kinetic energy management, Haddon’s matrix and road safety, Bristol City Council, 2015