Bringing a vehicle to a complete stop on a level roadway usually requires only a single application of the brakes. The degree of application will be determined by the speed, weight and degree of emergency.
When the speed of the vehicle has been decreased sufficiently, ease off the amount of brake application and the actual stop will be gradual. The professional driver can perfect these stops by practising the amount of brake application release to prevent a jerk-back at the actual stop. This braking skill, coupled with factors of:
- looking ahead to time stops,
- maintaining safe following distance, and
- setting speed in relation to the distance you can see ensures a smooth stop every time (most passengers judge the driver's skill based on this).
Stopping on an icy road surface will require you to threshold brake to prevent the wheels from locking up. On vehicles equipped with anti-lock brakes, apply according to the vehicle manufacturer's instructions. A slow revolving wheel on an icy surface will be more effective than a locked wheel skidding on icy surfaces. To proceed down a steep grade, select a gear low enough to control the speed (usually one gear below the one you would use to climb the same hill) and use engine retarder brakes if so equipped. This should reduce the need to use your brakes to a point where they will overheat and your air supply will not be seriously depleted.
To determine the safe speed to travel down a steep grade, remember one factor: the speed which will allow a safe stop at any time while on the hill.
If you are unable to stop to prevent a collision, the fact that you were travelling downhill is no excuse; your speed should have been adjusted to the condition.
The driver who claims the excuse for speeding was because they were going downhill is neither a professional nor a defensive driver. The professional driver uses brakes and gear selection to control the vehicle and doesn’t need excuses. Note: Trailers weighing over 1,360 kg (3,000 lb.) must be equipped with brakes.
Large vehicles such as truck-trailer and semi trailer units have engine governors which control the maximum rpm at which the engine may be operated. When descending steep grades, special caution should be taken by maintaining correct speed in relation to gear selection to keep the engine rpm at least 200 to 300 below the maximum governed rpm. In other words, if the momentum of the unit is allowed to push the engine over its governed speed, engine damage could occur.
Drivers of trucks equipped with engine brake retarders must avoid unnecessary use of these systems in cities and residential areas. The use of retarders on vehicles which are inadequately muffled results in a harsh irritating noise. The engine brake retarder develops its retarding efficiency at higher engine rpm, therefore, gear selection is important.
The gear selected to descend the grade is usually determined by the driver's decision of the gear ratio needed to climb the grade. Gear selection should be made before descending the grade, rather than on the downgrade, to minimize the chance of missing a shift. The driver of a truck equipped with a retarder system must be familiar with the manufacturer's recommended use of the retarder under all road and weather conditions.
In a combination of vehicles (such as a truck and trailer, or power unit with a semi trailer unit) equipped with an air brake system, the trailer brakes are applied along with the tractor brakes by use of the foot control valve. This is often referred to as "balanced braking." The application pressure of the trailer brakes is equal to the application pressure of the tractor brakes. The trailer brakes may be applied independently of the tractor brakes by use of the hand control valve. If the driver wishes, the amount of application on the trailer brakes may be increased during a foot valve application by using a higher application with the hand valve. Trailers equipped with electric or vacuum brakes are operated in a similar manner.
Brakes must be applied cautiously when the vehicle is negotiating a curve or travelling on wet or icy surfaces. Over-braking could result in jackknifing or skidding.
Water on roadways
Water entering brake drums will reduce the braking effort, so avoid running through large amounts of water whenever possible. Place a slight drag on the brakes when it becomes necessary to run through water, to reduce the amount of water admitted to the drums and shoes. During excessively wet conditions, or after passing through water, test the brakes. It may be necessary to drag the brakes slightly for a short distance to dry them out and restore normal braking. Always reduce your speed before driving through large pools of water on the road.