Page 53 - Draft 2023 2024 CDL Manual w Modernization Info

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COMBINATION 6.1 - Driving Combination change, the crack-the-whip effect can tum 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
Cou lin and truck becomes easier to tum over. Fully loaded over. Follow far enough behind other vehicles
p
g
Uncou lin ............... 6.4 rigs are ten times more likely to roll over in a (at least 1 second for each 10 feet of your vehicle
g
p
length, plus another second if going over 40
crash than empty rigs.
The following two things will help you pre­
mph). Look far enough down the road to avoid
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 Control your speed whether fully loaded or
with trailer). The information is only to give you possible. (Cargo distribution is covered in Sec­
the minimum knowledge needed for driving tion 3 of this manual.) empty. Large combination vehicles take longer
to stop when they are empty than when they
common combination vehicles. You should Rollovers happen when you tum too fast.
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
when fully loaded. poor traction and make it very easy to lock up
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 " b obtail" tractors (tractors without
the-whip" effect. When you make a quick lane semitrailers). Tests have shown that bobtails
- 1.0 I.S 20 2.5 3.0 !.5 40
INFLUENCE OF COMBINATION TYPE ON REARWARD AMPLIFICATION

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somirailor
with 45 fl
7
•3 axle tractor •
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with 27 fl
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doubk> 45 ft. w
lf.ailOB .di., - �
7
ll
·e..1r.in ., • .. • ..
doublG 27 It
ti il�n -iUI -
•Rocky 11 I
mountain w • •
double - 4S ft.
•C:al�om�hucll e;UQ t;=;
11111 trallor
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double- 27 it.
71 II I
•Tripl9 27 IL • • • • •
u.allon

Figure 6.1
Image courtesy ©iStockphoto.com/MCCAIG
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