In an air brake system, the first tank that receives compressed air has a safety valve that releases air if the pressure gets too high. It is usually set to open at 150 psi. If the valve must open, there is a fault in the system that should be repaired by a mechanic.

While inspecting a coupling, you should go under the trailer and look into the back of the fifth wheel. Ensure that the fifth wheel jaws are secured around the shank of the kingpin.

Tractors without semi-trailers are referred to as bobtail tractors. Operating a bobtail tractor requires drivers to exercise caution.

When backing up to couple a trailer, you should position the tractor directly in front of the trailer. Trying to couple while backing at an angle could cause the trailer to move and the landing gear to break.

When pressing the brake pedal in a vehicle with S-cam brakes, air will enter the brake chambers. The added air pressure will push out the rods and move slack adjusters, twisting the brake camshafts.

At speeds below 40 mph, you should allow at least one second of following distance for every 10 feet of your vehicle. Follow the same formula when traveling at faster speeds, then add one additional second to your following distance. Remember that larger vehicles require more space to stop than smaller vehicles.

When trailer air lines are color-coded, the service lines are generally blue and the emergency lines are generally red.

Triple combination trailers are most vulnerable to the "crack-the-whip" effect.

The brakes in an air brake system use compressed air to function properly.

If the low pressure warning signal activates while you are driving, it is important that you safely exit the roadway as soon as possible and park your vehicle. If the air pressure gets too low, the brakes will no longer work well enough for you to stop safely.

A trailer tends to swing around, potentially resulting in a trailer jackknife, if its wheels lock up.

Rollovers happen when a vehicle is driven too fast. To reduce the risk of rollover, make sure the weight of cargo is loaded low to the ground, and that you take turns and curves slowly.

In an air brake system, a low pressure warning signal should activate if the pressure in the air tanks falls to a level below 60 psi. This signal may be in the form of a warning light or a wig wag.

Driving combination vehicles requires more skill than driving single commercial vehicles. Combinations are generally longer, generally heavier, and are more vulnerable to rollover.

The trailer service air line is also referred to as the control line or signal line.

In a vehicle with air brakes, the brake lights are activated when the brake pedal is pushed and air pressure moves an electric switch. With the application of air pressure, the switch will then turn on the brake lights.

Combination vehicles require more skill to drive than single vehicles. Combination vehicles are usually longer and heavier, and are more vulnerable to rollovers.

To reduce the risk of a rollover, the weight of cargo in a trailer should be kept as low to the ground as possible. Weight should not be placed primarily on one side of the trailer as this could make the trailer lean, increasing the risk of a rollover.

Vehicles with Anti-Lock Braking Systems (ABS) have yellow malfunction lamps.

Before starting down a hill, be sure to switch into a low gear. Gravity will increase your vehicle's speed as you travel downhill.

Many large CMVs are equipped with air brakes. An air braking system uses compressed air to operate.

If your trailer starts to skid while you are braking, you should release the brakes and allow them to begin to regain traction. Once its wheels have regained their grip on the road, the trailer will begin to straighten out and follow the tractor.

A wig wag is a type of low air pressure warning device in an air brake system. It drops a mechanical arm into the driver's view when the air pressure in the tanks falls below 60 psi.

Before coupling together a tractor and a trailer, you should make sure the trailer is at the proper height. If the trailer is too low, the trailer nose may be damaged. If the trailer is too high, it may not be able to couple correctly.

Air lines are sometimes color-coded to help drivers avoid mistakes when coupling glad hands. Typically, blue is used for service lines and red is used for emergency lines.