Pennsylvania CDL Permit Test - Double

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.

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.

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.

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.

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.

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.