The tractor protection valve keeps air in the trailer's braking system should the trailer break away or develop a leak. A loss of air pressure in the emergency line will cause the tractor protection valve to open and the emergency trailer brakes to activate.

Reduce your speed as you approach a railroad crossing. Remember that you will not necessarily be able to hear a train, and don't assume that signals will warn you of its approach. Never try to outdrive an approaching train at a railroad crossing.

Dollies manufactured on or after March 1, 1998 must have Anti-Lock Braking Systems (ABS). A dolly with ABS must be identifiable by a yellow lamp on its left side.

In rainy weather, roads are often at their most slippery when the rain first begins to fall. Fresh rainwater mixes with oil and grease on the road to form a slick film. As the rain continues, this mixture will eventually wash away.

Always downshift before entering a curve. Decreasing your speed before entering the curve will allow you to maintain better control over the vehicle throughout the curve.

If you are unsure if a trailer is equipped with an Anti-Lock Braking System (ABS), look under the vehicle for the electronic control unit and wheel speed sensor wires coming from the back of the brakes.

Be especially cautious when driving on ice that has begun to melt. Ice that is wet is much more slippery than ice that is dry.

Large combination vehicles take longer to stop when they are empty than when they are loaded. The decreased weight causes a vehicle's wheels to have decreased traction on the surface of the road.

Be cautious when driving near people who are not paying attention to the road. Be wary of road workers, drivers who are engaged in conversation with passengers, and children near the road.

Compressed air in an air brake system usually contains a certain amount of water and compressor oil. The water and oil can damage the brakes if left to accumulate in the system. Tanks must be drained regularly to remove this build-up.

Railroad crossings that are not controlled by any type of traffic control device are known as passive crossings. The decision to proceed across tracks at a passive crossing is entirely up to the driver.

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 inspecting the convertor dolly, ensure that all components are present and in proper working condition. Be sure to check the upper and lower fifth wheel, the air lines, and the electric lines. The air lines should be securely attached to the proper glad hands and should not contain any leaks. They should be attached with enough slack to allow easy turning.

If you think the road surface may be becoming icy, you can check for ice on your vehicle by opening the window and feeling the front of the side mirror, mirror support, or antenna. If ice has formed on any of these items, the road is likely becoming icy as well.

Drivers with blocked vision may pose hazards to others on the road. Examples of such drivers include those who haven't scraped ice off of their windshields; those driving vehicles loaded with large items blocking the windows; and those who are driving rental trucks without being used to the limited rear visibility of a truck.

Both systems in a dual air brake system share a single air compressor. If the air compressor is damaged, neither system will be able to operate properly.

The three main factors that determine a person's blood alcohol concentration (BAC) are the amount of alcohol consumed, how quickly the alcohol is consumed, and the person's weight.

When a vehicle is traveling on a downward slope, the force of gravity will cause its speed to increase.

Defects in an exhaust system are very dangerous because they can cause poisonous fumes to enter the cab or sleeper berth.

Before slowing down, it is a good idea to flash your brake lights by lightly tapping your brake pedal a few times. This will warn drivers behind you of your plans to slow down.