FREE CDL Combination Vehicles Practice Test Online | Oregon 2024 Page 2 of 3
Train for FREE online with our Oregon CDL combination vehicle test. The official exam test consists of several obligatory parts, with all of them checking your knowledge of different blocks of road rules. If you need to obtain a OR combination license in 2021, practice as much as possible. Free sample tests published on our website will help you check and improve your knowledge and boost your grades. Please bear in mind that DMV requirements for issuing a combination license may vary from state to state.
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8 . What does the tractor protection valve do?
Ensures oil adequately lubricates the engine
The tractor protection valve keeps air in the tractor or truck braking system, should the trailer break away or develop a bad leak.
9 . In a vehicle equipped with an automatic tractor protection valve, the valve will pop out when:
Air pressure is above 45 psi.
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.
10 . Look for matching colors when coupling glad hands. Service lines are often:
Blue.
When coupling glad hands, make sure to couple together matching glad hands. To help drivers avoid mistakes, color coding is sometimes used. Service lines are often coded with the color blue and emergency lines are often coded with the color red.
11 . Trailers built before ____ are not required to have spring brakes.
Trailers built before 1975 are not required to have spring brakes. When parking a trailer without spring brakes, be sure to use wheel chocks to prevent the trailer from rolling.
12 . The trailer hand valve should not be used while you are driving because:
Never use the trailer hand valve while operating your vehicle. Using the trailer hand valve while driving can cause your trailer to skid.
13 . In a combination rig, it is best to make:
Slow, planned stops.
When driving a combination vehicle, it is important to brake well in advance and look far ahead of your vehicle to avoid the need for sudden stops. Making habits of these actions will help you prevent your trailer from jackknifing.
14 . Simply changing lanes can cause:
Other drivers to reduce their speed.
