- Too dangerous to drive during the day
- Less stable than regular commercial vehicles
- Just as stable as regular commercial vehicles
- More stable than regular commercial vehicles
From The CDL Manual
7.1 – Pulling Double/Triple Trailers
Take special care when pulling two and three trailers. There are more things that can go wrong, and doubles/triples are less stable than other commercial vehicles. Some areas of concern are discussed below.
- May not be safe for doubles or triples
- Will definitely be safe for doubles or triples
- Is 45 mph
- Is too slow for doubles or triples
From The CDL Manual
Prevent Trailers From Rolling Over —
To prevent trailers from rolling over, you must steer gently and go slowly around corners, on ramps, off ramps and curves. A safe speed on a curve for a straight truck or a single trailer combination vehicle may be too fast for a set of doubles or triples.
- The shoot-the-moon effect
- The roll-the-bones effect
- The crack-the-whip effect
- The spit-and-shine effect
From The CDL Manual
Crack-the-Whip Effect —
Doubles and triples are more likely to turn over than other combination vehicles because of the “crack-the-whip” effect. You must steer gently when pulling trailers. The last trailer in a combination is most likely to turn over. If you do not understand the crack-the-whip effect, study Section 6.1 and review Figure 6-1 on page 70.
- Tractor
- Last trailer
- First trailer
- Entire vehicle
From The CDL Manual
Crack-the-Whip Effect —
Doubles and triples are more likely to turn over than other combination vehicles because of the “crack-the-whip” effect. You must steer gently when pulling trailers. The last trailer in a combination is most likely to turn over. If you do not understand the crack-the-whip effect, study Section 6.1 and review Figure 6-1 on page 70.
- Increased stopping distance and looking farther ahead
- More critical parts requiring inspection
- These are all things that require increased awareness when driving doubles and triples
- Managing a larger space
From The CDL Manual
Inspect Completely —
There are more critical parts to check when you have two or three trailers. Check all of them by following the procedures described later in this section.
Look Far Ahead —
Doubles and triples must be driven very smoothly to avoid rollover or jackknife. Therefore, look far ahead so you can slow down or change lanes gradually when necessary.
Manage Space —
Doubles and triples take up more space than other commercial vehicles. They are not only longer, but also need more space because they cannot be turned or stopped suddenly. Allow more following distance. Make sure you have large enough gaps before entering or crossing traffic. Be sure you are clear at the sides before changing lanes.
- You must be especially careful
- They are easier to control
- Loss of traction is a bigger concern
- There is greater chance of a skid
From The CDL Manual
Adverse Conditions —
Be more careful in adverse conditions. In bad weather, slippery conditions and mountain driving, you must be especially careful if you drive double and triple bottoms. You will have greater length and more dead axles to pull with your drive axles than other drivers. There is more chance for skids and loss of traction.
- Set the emergency brakes
- Ruin the trailer brake system
- Release the emergency brakes
- Guarantee that the trailer will not move
From The CDL Manual
Secure second (rear) trailer:
If the second trailer does not have spring brakes, drive the tractor close to the trailer, connect the emergency line, charge the trailer air tank, and disconnect the emergency line. This will set the trailer emergency brakes (if the slack adjusters are correctly adjusted). Chock the wheels if you have any doubt about the brakes.
- The lighter trailer
- It doesn't matter
- The heavier trailer
- The shorter trailer
From The CDL Manual
Caution:
For the safest handling on the road, the more heavily loaded semi-trailer should be in first position behind the tractor. The lighter trailer should be in the rear.
- Removed
- Ignored
- Open
- Locked
From The CDL Manual
Move dolly to rear of first semi-trailer and couple it to the trailer.
Lock pintle hook.
- To couple a second (or third) trailer behind another trailer
- To convert AC electricity to DC
- Only in Canada
- Only in emergency
From The CDL Manual
Couple tractor and first semitrailer as described earlier:
A converter gear or dolly is a coupling device of one or two axles and a fifth wheel by which a semitrailer can be coupled to the rear of a tractor-trailer combination forming a double bottom rig.