- Is safer when braking
- Makes it harder to stop
- Makes it easier to stop
- Should never be attempted
From The CDL Manual
Brake Early —
Control your speed whether fully loaded or empty. Large combination vehicles take longer to stop when they are empty than when they are fully loaded. When lightly loaded, the very stiff suspension springs and strong brakes give poor traction and make it very easy to lock up the wheels. Your trailer can swing out and strike other vehicles. Your tractor can jackknife very quickly (see Figure 6-2 below). You also must be very careful about driving “bobtail” tractors (tractors without semitrailers). Tests show that bobtails can be very hard to stop smoothly. It takes them longer to stop than a tractor-semitrailer loaded to maximum gross weight.
- Lawn job
- Trailer jackknife
- Traffic jam
- Bald tire
From The CDL Manual
Prevent Trailer Skids —
When the wheels of a trailer lock up, the trailer will tend to swing around. This is more likely to happen when the trailer is empty or lightly loaded. This type of jackknife is often called a “trailer jackknife”
- Other drivers pointing and waving
- Smelling smoke
- Looking in the mirrors
- Hearing loud noises
From The CDL Manual
Recognize the skid.
The earliest and best way to recognize that the trailer has started to skid is by seeing it in your mirrors. Any time you apply the brakes hard, check the mirrors to make sure the trailer is staying where it should be. Once the trailer swings out of your lane, it is very difficult to prevent a jackknife.
- Apply the trailer brakes
- Stop using the brake
- Sound your air horn until you regain traction
- Immediately slam on the brakes
From The CDL Manual
Stop using the brake.
Release the brakes to get traction back. Do not use the trailer hand brake (if you have one) to “straighten out the rig.” This is the wrong thing to do because the brakes on the trailer wheels caused the skid in the first place. Once the trailer wheels grip the road again, the trailer will start to follow the tractor and straighten out.
- Release the brakes
- Watch your mirrors
- Keep the wheel straight
- Use the trailer hand brake
From The CDL Manual
Following is the procedure for stopping a trailer skid:
1. Recognize the skid. The earliest and best way to recognize that the trailer has started to skid is by seeing it in your mirrors. Any time you apply the brakes hard, check the mirrors to make sure the trailer is staying where it should be. Once the trailer swings out of your lane, it is very difficult to prevent a jackknife.
2. Stop using the brake. Release the brakes to get traction back. Do not use the trailer hand brake (if you have one) to “straighten out the rig.” This is the wrong thing to do because the brakes on the trailer wheels caused the skid in the first place. Once the trailer wheels grip the road again, the trailer will start to follow the tractor and straighten out.
- Lolly-gagging
- Off-tracking
- Side-tracking
- Dog-pedalling
From The CDL Manual
Turn Wide —
When a vehicle goes around a corner, the rear wheels follow a different path than the front wheels. This is called “offtracking” or “cheating.” Figure 6-4 on page 72 shows how offtracking causes the path followed by a tractor-semi to be wider than the rig itself. Longer vehicles will offtrack more. The rear wheels of the powered unit (truck or tractor) will offtrack some, and the rear wheels of the trailer will offtrack even more.
- Keep the rear of your vehicle close to the curb
- Go as slow as possible
- Swerve back and forth
- Wave them ahead on your left
From The CDL Manual
Steer the front end wide enough around a corner so the rear end does not run over the curb, pedestrians, other vehicles, etc. However, keep the rear of your vehicle close to the curb. This will stop other drivers from passing you on the right.
- Swing wide to the left before the turn
- Try to find a police officer to direct traffic
- Stop and sound the air horn to make sure other vehicles get out of the way
- Turn wide as you complete the turn, instead of before it
From The CDL Manual
Turn Wide —
If you cannot complete your turn without entering another traffic lane, turn wide as you complete the turn (see Figure 6-5 on page 72). This is better than swinging wide to the left before starting the turn because it will keep other drivers from passing you on the right. If drivers pass on the right, you may collide with them when you turn.
- When the trailer starts to skid
- Never use it while driving
- Only in emergency
- Traveling under 30 mph
From The CDL Manual
Trailer Hand Valve —
The trailer hand valve (also called the “trolley valve” or “Johnson bar”) works the trailer brakes. The trailer hand valve should be used only to test the trailer brakes. Do not use it in driving because of the danger of making the trailer skid. The foot brake sends air to all the brakes on the vehicle (including the trailer(s’). There is much less danger of causing a skid or jackknife when using just the foot brake.
- Only to test the trailer brakes
- When parking
- When the vehicle starts to skid
- Along with the foot brakes
From The CDL Manual
Trailer Hand Valve —
The trailer hand valve (also called the “trolley valve” or “Johnson bar”) works the trailer brakes. The trailer hand valve should be used only to test the trailer brakes. Do not use it in driving because of the danger of making the trailer skid. The foot brake sends air to all the brakes on the vehicle (including the trailer(s’). There is much less danger of causing a skid or jackknife when using just the foot brake.
Never use the hand valve for parking because all the air might leak out, unlocking the brakes (in trailers that do not have spring brakes.) Always use the parking brakes when parking. If the trailer does not have spring brakes, use wheel chocks to keep the trailer from moving.