Stopping distances: speed and braking

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[Speaking - Professor Barry Watson Direct CARRS-Q, QUT]

The simple truth about speeding is that the faster you go the longer it takes to stop.

Here’s a comparison.

This is a car travelling at 60km/h and braking suddenly.

Here’s the same car, travelling at 67km/h and braking at the exact same point.

This time the car hits, still travelling at 30km/hr. The difference could be a matter of life or death.

In an emergency, the average driver takes about 1.5 seconds to react. Stopping  distances increase exponentially the faster you go.

You can also access this infographic information in text form.

The stopping distances on the infograph are calculated based on the following assumptions:

• In an emergency the average  driver takes approximately 1.5 seconds to react
• A modern vehicle with good brakes and tyres, after braking, is capable of stopping at approximately 7 m/s².
• A dry road that is sealed and level enables good friction between the tyres and the road to help stop the vehicle sooner.  Scientifically, it has a coefficient of friction of approximately 1.
• A wet road that is sealed and level has less friction between the tyres and the road which increases the stopping distance of a vehicle.  Scientifically, the coefficient of friction of approximately 0.7.

The stopping distances in the graph are generic and may be influenced by a number of driver, vehicle and environmental factors:

Driver factors	Vehicle factors	Environmental factors
Attention	Vehicle age	Road surface
Fatigue	Type and condition of brakes	Road gradient
Impairment due to alcohol and drugs	Type and condition of  tyres, including tyre pressure	Road alignment
Vision issues	Safety features fitted to  the vehicle for example ABS, ESC, EBA, etc.	Weather conditions
Driver age and experience	Vehicle weight
Hazard perception ability	Towing a trailer or  carrying a heavy load