Combination #1
Combination Vehicles Practice Test | District Of Columbia 2026 #1 Page 3 of 3
Train for FREE online with our District Of Columbia 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 DC combination license in 2026, 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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15 . What can the “crack-the-whip” effect do?
Make trucks decelerate.
The "crack-the-whip" effect can cause a trailer to turn over during a lane change. To avoid this phenomenon, drivers should make lane changes at slow, safe speeds.
16 . If a trailer's spring brakes do not release when you push the tractor air supply control, you should:
Drive normally without checking anything.
It is important that all of your vehicle's equipment is in proper working condition before you begin a trip. If a trailer's spring brakes do not release when you push in the tractor air supply control, you should make sure the air line connections are properly attached and sealed.
17 . To prevent a rollover, cargo should be:
Loaded with most weight on the driver’s side of a trailer.
To reduce the risk of rollover, the weight of cargo in a trailer should be centered and spread out as much as possible. The weight of the cargo should also be kept as low to the ground as possible.
18 . 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.
19 . If colors are being used to distinguish glad hands, which color is used for service lines?
Blue
When trailer air lines are color-coded, the service lines are generally blue and the emergency lines are generally red.
20 . Compared to other commercial motor vehicles, combination vehicles need more space on the road because they are longer and they:
Swerve more often.
