Lesson 1/ Learning Event 2
Special purpose vehicles
These vehicles are made to do a certain job that a general purpose vehicle or special equipment
vehicle cannot do.
One example of this is a wrecker. The frame of the general purpose vehicle chassis would not be
strong enough to take the load. Another example is the truck-tractor that you see pulling a large
cargo trailer on the highway.
Truck-tractors are made for towing and not for carrying cargo. The frame is shorter than a cargo-
carrying truck.
TRAILER CLASSIFICATION
Some vehicles you will work with are made to be towed. These vehicles are trailers and
semitrailers.
Trailers
These vehicles have a drawbar, or tongue, in the front, to be attached to the pintle or coupling
mounted on the rear of the vehicle that does the towing. The eye at the end of the trailer's tongue
that hooks into the pintle is called a lunette.
Most of the trailers in use today are two-wheeled. However, you will see some four-wheeled
trailers (or "full trailers").
Trailers are made in such a way that their wheels support most of the weight of the cargo they are
carrying.
Semitrailers
These are also vehicles made to be towed, but there is one big difference between a semitrailer and
a tongue-type trailer. The front part of the semitrailer is supported by the towing vehicle. This
means the towing vehicle carries a lot of the cargo weight.
The vehicle that carries some of the load and tows a semitrailer is called a truck-tractor. The
semitrailer is connected to the "fifth wheel" of the truck-tractor or may be supported by means of a
"dolly." A dolly is another set of wheels, a frame, and a fifth wheel.
When the dolly is placed under the semitrailer, it becomes a full trailer and can be towed using an
ordinary truck.
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