delivery agent. You must complete the
Program in order to obtain the air brake
“Q” endorsement on your driver’s
licence. This endorsement is required to
operate any vehicle with air brakes.
How long does
it take to stop a
In order to stop a moving vehicle, a driver
needs to perform three actions:
• See - a hazard
• Think - decide to stop
• Do - place foot on the brake pedal
until vehicle stops
The function of any braking system is to
slow the motion of a moving vehicle. Heavy
commercial vehicles take more time and
more distance to stop than smaller vehicles.
More braking force is needed to overcome
their weight and forward motion.
The distance a commercial vehicle
needs to stop is affected by the following
1 Brake condition. All the brakes on
a vehicle must share the task in the
same way. If one or more brakes are
not properly aligned or maintained, the
remaining brakes will have to generate
more friction. This means that it will take
longer to stop the vehicle.
2 Traction. Traction is the friction
between the road surface and the area
where the tire contacts that surface.
The amount of traction a vehicle has
• the condition of the road
• how much tire contact there is with
the road surface
• the condition and inflation pressure
of the tires
• the gross vehicle weight (GVW)
of the vehicle
The more traction the vehicle has, the
less time and distance it will take to stop.
There is the most traction just before all
the wheels lock up. There is less traction
when the wheels are skidding.
3 Weight (GVW). A heavy vehicle, even
though it has better traction, needs more
time and distance to stop. When the
weight is doubled, the amount of force
needed to stop the vehicle is doubled,
and it will take about twice as long for
that vehicle to stop (Figure 1 - page 42).
4 Speed. The greater the speed, the more
time and distance are needed to stop.
Figure 2 illustrates that doubling the
vehicle speed means that four times
the braking force is required to bring
the vehicle to a stop. Figure 3 illustrates
that if both the speed and weight are
doubled, the amount of force required
to stop the vehicle will be increased by
The total stopping distance to bring a
vehicle to a complete stop is measured
from the time a driver realizes the need to
apply the brakes until the vehicle comes to
a full stop. The time it takes for a vehicle to
stop is affected by four factors:
1 Perception time is the amount of
time it takes a person to realize the
need to stop the vehicle. The average
perception time is about three-quarters
of a second. Perception time can
increase if a person is not paying