TRANSPORTING LOADS - Continued
The semitrailer, with its towing vehicle, will have different operational characteristics based on gross
weight, differences between loaded and unloaded weight and suspension characteristics. Safe operating
limits are affected by the interaction of the vehicle characteristics, load, road surface, weather, operator
skill, and vehicle speed.
Before operating the semitrailer, ensure that all the operating procedures contained in this manual are
Appropriate procedures for services and PMCS (WP 0033) will be completed prior to operating the semitrailer.
See Payload Configurations at the beginning of this work package to determine if a permit is required prior
General. When driving the towing vehicle and semitrailer, the overall length must be kept in mind, both
when passing other vehicles and when turning. Because the unit pivots at the fifth wheel, backing is
Road Surfaces. Uneven terrain, steep grades, crowned roads, and unimproved road surfaces can
introduce forces that will make handling difficult. Even a vehicle that is properly maintained and loaded
can be hazardous when excessive speed and certain road conditions are combined.
Grades. Operation on grades requires caution. Use the same gear in descending a long grade as when
ascending. Gear selection should be made before descending a grade to minimize the chance of a
missed shift. Avoid excessive use of brakes on long down-grades in order to maintain air pressure and
prevent overheating of the brakes.
Side Slopes. This semitrailer is not designed to be operated on excessive (15 percent) side slopes. The
semitrailer can be safely operated, with or without payloads, on side slopes commonly encountered on
highways or unimproved roads.
Turning. When turning corners, allow extra room. The semitrailer wheels will follow a track that is inside
the radius of the towing vehicle wheels. For right turns, drive about halfway into the intersection and then
cut sharply to the right. The forces affecting the stability of a tractor semitrailer combination are increased
during turning. The smaller the radius, the greater the force trying to pull the vehicle over. Therefore, the
tighter the curve, the slower the speed must be in order to avoid a rollover.
In normal operation, when the operator applies the brakes, the towing vehicle and the semitrailer brakes are
applied at the same time. Brake pressure should be applied gradually and smoothly. The semitrailer brakes may
be applied separately by using the semitrailer hand brake control lever in the towing vehicle. (Check towing
vehicle TM for proper stopping operation.) Extreme caution should be exercised when using only the semitrailer
brakes. Some benefit may be gained on slippery surfaces by slowly applying the semitrailer brakes before the
towing vehicle brakes, reducing the possibility of jackknifing the semitrailer. However, it is very dangerous to use
only the semitrailer brakes on long down-grades. Doing so will cause the semitrailer brakes to heat up and fade.
The towing vehicle brakes alone will not be able to stop the combined vehicle load. Selecting a lower gear before
beginning a long downgrade is the safest, most effective way to maintain control of the vehicle combination.