Page 52 - DDS Commercial Driver Manual 2021-2022

SECTION 6

COMBINATION 6.1 – Driving Combination change, the crack-the-whip effect can turn the
VEHICLES Vehicles Safely trailer over. There are many accidents where
only the trailer has overturned.
“Rearward amplification” causes the crack-
Combination vehicles are usually heavier, the-whip effect. Figure 6.1 shows eight types of
This Section Covers longer, and require more driving skill than combination vehicles and the rearward ampli-
single commercial vehicles. This means that
fication each has in a quick lane change. Rigs
Driving drivers of combination vehicles need more with the least crack-the-whip effect are shown
knowledge and skill than drivers of single
Combinations .............6.1 vehicles. In this section, we talk about some at the top and those with the most, at the bot-
tom. Rearward amplification of 2.0 in the chart
important safety factors that apply specifically means that the rear trailer is twice as likely to
Combination Vehicle to combination vehicles. turn over as the tractor. You can see that triples
Air Brakes .................. 6.2 6.1.1 – Rollover Risks have a rearward amplification of 3.5. This means
you can roll the last trailer of triples 3.5 times
More than half of truck driver deaths in as easily as a five-axle tractor.
Antilock Brake crashes are the result of truck rollovers. When Steer gently and smoothly when you are pull-
Systems ..................... 6.3 more cargo is piled up in a truck, the “center of ing trailers. If you make a sudden movement
gravity” moves higher up from the road. The with your steering wheel, your trailer could tip
Coupling and truck becomes easier to turn over. Fully loaded over. Follow far enough behind other vehicles
Uncoupling ............... 6.4 rigs are ten times more likely to roll over in a (at least 1 second for each 10 feet of your vehicle
length, plus another second if going over 40
crash than empty rigs.
mph). Look far enough down the road to avoid
The following two things will help you pre-
Inspection vent rollover--keep the cargo as close to the being surprised and having to make a sudden
Combinations ............ 6.5 ground as possible, and drive slowly around lane change. At night, drive slowly enough to
turns. Keeping cargo low is even more impor- see obstacles with your headlights before it is
tant in combination vehicles than in straight too late to change lanes or stop gently. Slow
trucks. Also, keep the load centered on your down to a safe speed before going into a turn.
This section provides information needed rig. If the load is to one side so it makes a trailer
to pass the tests for combination vehicles lean, a rollover is more likely. Make sure your 6.1.3 – Brake Early
(tractor-trailer, doubles, triples, straight truck cargo is centered and spread out as much as
with trailer). The information is only to give you possible. (Cargo distribution is covered in Sec- Control your speed whether fully loaded or
the minimum knowledge needed for driving tion 3 of this manual.) empty. Large combination vehicles take longer
common combination vehicles. You should Rollovers happen when you turn too fast. to stop when they are empty than when they
also study Section 7 if you need to pass the Drive slowly around corners, on ramps, and are fully loaded. When lightly loaded, the very
test for doubles and triples. off ramps. Avoid quick lane changes, especially stiff suspension springs and strong brakes give
poor traction and make it very easy to lock up
when fully loaded.
the wheels. Your trailer can swing out and strike
6.1.2 – Steer Gently other vehicles. Your tractor can jackknife very
quickly. You also must be very careful about
Trucks with trailers have a dangerous “crack- driving “bobtail” tractors (tractors without
the-whip” effect. When you make a quick lane semitrailers). Tests have shown that bobtails
INFLUENCE OF COMBINATION TYPE ON REARWARD AMPLIFICATION

Figure 6.1
Image courtesy ©iStockphoto.com/MCCAIG

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