Braking Distance 

Braking Distance

The distance a car travels while it is trying to stop is called the braking or stopping distance.

Types of Tires

Braking Distance

The slope or grade of the road and the frictional resistance between the road and the car’s tires can affect the braking distance.

Eg. Car with new tires on a dry, level road will have a shorter braking distance than one with worn tires on a wet road.

Explaining Breaking Distance

Braking distance is proportional to the square of the velocity of the vehicle.

Eg. If you double your speed, the braking distance increases four times (2 ). If you triple your speed, your braking distance increases nine times (3 ).

Formula for Breaking Distance Braking distance is also dependent upon the

friction between the two surfaces. We account for the frictional effects by using a mathematical constant for different kinds of surfaces.

d = kv2

d = braking distance k = frictional constant (different for each

surface) v = velocity (m/s)

Types of Surfaces

Try an example…

Eg. Find the braking distance for a car with a velocity of 50 km/h on dry pavement.

Reaction Time

Calculations for braking distance are for ideal cases only. In reality the driver’s reaction time also plays a role.

Reaction Distance = velocity x time

Try an example… Eg. A car is moving at 50 km/h on dry

pavement. Suddenly, 34 m away, a small dog darts into the roadway. Typically the driver takes 1.5 seconds to react. What is the total reaction distance?

Try an example… Eg. A car is moving at 50 km/h on dry

pavement. Suddenly, 34 m away, a small dog darts into the roadway. Typically the driver takes 1.5 seconds to react. What is the total breaking distance?

Total Stopping Distance Therefore, when looking at the length that it takes a car to come to a stop we must look at the reaction time of the driver, as well as the braking distance.

Total Stopping Distance = reaction distance + braking distance

Try an example…

Eg. A car is moving at 50 km/h on dry pavement. Suddenly, 34 m away, a small dog darts into the roadway. Typically the driver takes 1.5 seconds to react. What is the total stopping distance?