BC Transit – Air Brake Course

A typical tractor-trailer trailer unit connected and ready for work.
The unit is called a semi-trailer because the
towing vehicle, or tractor, actually carries part
of the load. The trailer has no front axle and
would fall on it’s nose if it disconnected from
the tractor.
The tractor pictured here is a tandem axle. (It
has two sets of driving axles.) Some have only
one and are called “single axle tractors.”
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