# Speed is always a factor

When people say "speed wasn't a factor" in a collision, they are misleading you. It's always a factor.

You will often the phrase in the press "Speed wasn't a factor" after a crash. What they are really saying is that the driver was (given available evidence) **not going excessively beyond the speed limit**. As it turns out **speed is always a factor**.

There are a few things that determine if you will survive collision with an object, simplified they are its: *mass*, *velocity* and *shape*.

We'll leave *shape* out of this for the moment, because that's a different subject. Let's focus on the amount of kinetic energy that impacts an object when it's hit by a vehicle. We'll also ignore reaction times from all parties and other things.

Focusing on mass and velocity the amount of kinetic energy is:

`kinetic energy = 0.5 * mass * velocity`

^{2}

Mass has an effect on kinetic energy, but velocity has a much bigger effect, because it's squared.

- A 10kg weight travelling at 1 km/h has 0.38 Joules of kinetic energy.
- A 1kg weight travelling at 10km/h has 3.8 Joules of kinetic energy.
- A 0.016kg bullet travelling at 1,296km/h has 1036.8 Joules of kinetic energy
^{1}.

Bullets don't weigh much, but they travel really, really, really fast and kill people.

Or to put it another way, would you rather get hit by a truck travelling 1km/h or a car travelling 100km/h? The car will kill you, the truck might knock you over.

Regardless of what the speed limit is all that matters is how fast that vehicle is moving when it hits you. Survivability rates drop dramatically for a pedestrian hit by a car as speed increases ^{2}.

- At 30km/h your chance of surviving is 90%.
- At 40km/h your chance of surviving is 60%.
**At 50km/h your chance of surviving is 10%**.

The difference between 30km/h and 50km/h is basically the difference between life and death. **Speed is always a factor** and it will determine if you survive a collision or not.

When the police or press say "speed was not a factor", what they are really saying is that society, traffic engineers and politicians have already decided that convenience of drivers outweighs your chance of surviving a collision.