Tennessee CDL Permit Test - Double

In newer vehicles with air brakes, the parking brakes are controlled by a diamond-shaped yellow knob. Pull the knob out to activate the parking brakes and push it in to release them.

In vehicles equipped with an automatic tractor protection valve, the valve will pop out if air pressure drops to a level between 20 and 45 psi. When the valve pops out, the protection valve will close, stopping the flow of air.

If someone is tailgating you, it is a good idea to open up the space ahead of your vehicle to make it easier for the driver to pass you. Increasing your speed is not a good idea because the driver may continue to tailgate you at the higher speed, only increasing the danger.

If a tractor-trailer is so equipped, the trailer brake hand valve can be used to stop the vehicle from rolling back when being started from a stop.

When inspecting a vehicle's suspension, you should look for broken or missing leaves in the leaf springs. Any defect of this kind is dangerous. If one-fourth or more of the leaves are missing from any leaf spring, the vehicle must be put out-of-service.

An empty combination vehicle will come to a complete stop more slowly than a fully-loaded vehicle. The stiff suspension springs and strong brakes will have lower traction on a light trailer than they would if the vehicle carried more weight.

If you begin to feel sleepy while driving, the only safe response is to stop driving and get some sleep. Attempting to fight off exhaustion is dangerous and a major cause of fatal crashes. Stimulants are not a safe solution because they may help keep you awake but will not make you more alert. Once stimulants wear off, you will be even more tired than you were originally.