20 Tests
CDL Combination Vehicles Practice Test Online | District Of Columbia 2021
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 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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1 . When driving a trailer with ABS, you should:
Try to not brakes as often as you would when driving a vehicle without ABS.
When driving a tractor-trailer combination equipped with an Anti-Lock Braking System (ABS), you should brake in the same manner that you would if operating a vehicle without ABS.
2 . An air supply control in its "emergency" position will:
Accelerate the vehicle.
Tractor protection controls in older vehicles may be operated by levers instead of knobs. If an air supply control is set in its "emergency" position, the air supply will be stopped and the trailer emergency brakes will be applied.
3 . To help prevent rollovers, you should:
Keep the load on one side of the trailer.
To lower the risk of a rollover, load your cargo as closely to the ground as possible. To further reduce this risk, take curves and corners slowly.
4 . Having ABS on only one axle:
Will cause extra strain on the other axles.
Having an Anti-Lock Braking System (ABS) on only the trailer, or even on just one axle, will still provide a driver with additional control over the trailer when braking.
5 . When lightly loaded, combination vehicles:
Should be loaded with most of the weight in the rear of the trailer.
When a combination vehicle is lightly loaded, it may have poor traction. It is very easy for wheels to lock up on lightly-loaded vehicles when they are being stopped.
6 . When a combination vehicle goes around a corner:
It is acceptable for street signs to be knocked over if they are too close to the road.
When a vehicle goes around a corner, the rear wheels follow a different path than the front wheels. This is called off-tracking. This effect is especially pronounced on vehicles with trailers.
7 . Push in the trailer air supply control to:
Supply the trailer with air.