In addition to the above factors, a driver must understand what is meant by the term ‘stopping distance’. Stopping distance consists of three factors:

Driver’s reaction time + brake lag + braking distance.

REACTION TIME: The time it takes from the moment a hazard is recognized to the time the brake is applied, approximately 3/4 of a second. (Reaction time is often called ‘thinking time’.)

BRAKE LAG: The time the air takes to travel through a properly maintained air brake system, approximately 4/10 of a second.

BRAKING DISTANCE: The actual distance the vehicle travels after the brake is applied until the vehicle stops.

(The distance depends on the ability of the lining to produce friction, the brake drums to dissipate heat and the tires to grip the road.)

The professional driver never takes the brakes for granted. The braking system must be tested and the adjustment checked before placing the vehicle into service. The professional understands the braking system, realizes the capabilities and limitations and learns to use them to the best advantage.

Heavy vehicles require powerful braking systems that are obtained by use of mechanical leverage and air pressure. Brakes must be used keeping in mind the heat generated by friction. If the heat becomes too great, braking effectiveness will be lost. The heavier the load and the faster the speed, the greater the power needed to stop.

Stopping distance is also affected by the driver’s reaction time, brake lag and braking distance. The professional driver is well aware that the vehicle, even with properly adjusted brakes, will not stop as quickly as a passenger vehicle.