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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
vehicle?

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
four factors:
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
   depends on: 
   • 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
   eight times.

Stopping distance

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 

CHAPTER FOUR                                                                                OPERATING CLASS 1 VEHICLES  41

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