CDL General Knowledge Practice Test 2025

You should downshift before starting down a hill and before entering a
curve. You should upshift when the engine reaches the top of the tachometer
range.

There should be at least 4/32 inch tread depth in every major groove on the
front tires; 2/32 inch tread on other tires. No fabric should show through the
tread or sidewall.

Black ice is a thin layer of ice that is clear enough that you can see the road underneath. Any time the temperature is below freezing and the road looks wet, look out for black ice.

Before you begin backing a vehicle, you and your helper should agree on
a set of hand signals; the most important signal being the signal for “stop”.

When driving in very hot weather, you should inspect the tires every 2 hours or every 150 miles. Air pressure increases with temperature. If a tire is too hot to touch, remain stopped until the tire cools off. Otherwise the tire may blow out or catch fire.

During very hot weather, do not let air out of tires or the tire pressure will
be too low when the tires cool off.

Vehicles must be equipped with the following emergency equipment: Fire extinguisher(s); Spare electrical fuses (unless equipped with circuit breakers); Warning devices for parked vehicles (for example, 3 red reflective warning triangles, 6 fuses, or 3 liquid burning flares).

Missing or broken mounting brackets are exhaust system defects.

Many people cannot tell when they are about to fall asleep. If you notice
any signs of fatigue, do not try to “power through”; stop driving and go to sleep
for the night or take a 15 - 20 minute nap.

Hydroplaning is more likely when tire pressure is low or tread is worn.

Antifreeze helps the engine under hot as well as cool conditions.

If an aggressive driver is involved in an accident, you should a safe
distance from the accident scene and wait for the police to arrive.

The heavier the vehicle, the more work the brakes must do to stop it and
the more heat they absorb. The brakes, tires, springs, and shock absorbers on
heavy vehicles are designed to work best when the vehicle is fully loaded.
Empty trucks require greater stopping distances because an empty vehicle has
less traction

You must turn your headlights on a half hour after sunset and a half hour
before sunrise; when visibility is not sufficient to clearly see a person or vehicle
for a distance for 1000 feet; and if snow, rain, fog, or other hazardous weather
condition require the use of windshield wipers.

Pay attention to the engine speed (rpm) and road speed (mph) to know
when to shift

The following vehicles can get stuck on a raised crossing: Low slung
units (lowboy, car carrier, moving van, possum belly livestock trailer); single
axle tractor pulling a long trailer with its landing gear set to accommodate a
tandem axle tractor

A torque rod is part of the suspension system, not the steering system.

Wheel bearing seals should be checked for leaks.

If there is no white stop line painted on the pavement of a railroad
crossing, vehicles that are required to stop must stop no closer than 15 feet or
more than 50 feet from the nearest rail.

When your drive wheels have poor traction, the retarder may cause them
to skid. You should turn off the retarder whenever the road is wet, icy, or snow
covered

If your brakes fail on a long downgrade, your best bet is an escape ramp.
Ramps are usually located a few miles from the top of the downgrade. If no
escape ramp is available, take the least hazardous escape route you can, such as
an open field or a side road that flattens out or turns uphill.

To test hydraulic brakes for leaks, pump the pedal 3 times. Then apply firm
pressure to the pedal and hold for 5 seconds. The pedal should not move. If it
does, there may be a leak or other problem.

The proper braking technique when going down a long and/or steep downgrade, is to 1. Apply the brakes just hard enough to feel a definite slowdown 2. Release brakes after speed has been reduced to 5 mph below your “safe” speed 3. When your speed has increased to the your “safe” speed, repeat steps 1 and 2

During a vehicle inspection test, you should put the starter switch key in
your pocket so someone else will not move the truck while you are under it.

A vehicle inspection should be done before, during, and after a trip. After
the trip, day, or tour of duty, you should fill out a report listing any problems you
found. During a trip, you should inspect the vehicle within the first 50 miles and
then every 150 miles or 3 hours (whichever comes first).

For vehicles with automatic transmissions, you can select a low range to
get greater engine braking when going down grades. The lower ranges prevent
the transmission from shifting up beyond the selected gear. It is very important
to use this braking effect when doing down grades.

You should use a helper because there are blind spots that you cannot see. The helper should stand near the back of your vehicle where you can see the helper.

You need at least 1 second for each 10 feet of vehicle length at speeds
below 40 mph. At speeds greater than 40 mph, add an extra second.

It takes a typical tractor trailer at least 14 seconds to clear 1 track and
more than 15 seconds to clear a double track.

If you must stop on or by a one way or divided highway, place warning
devices 10 feet, 100 feet, and 200 feet toward approaching traffic. If you stop on
a 2 lane road carrying traffic in both directions or on an undivided highway,
place warning devices within 10 feet of the front or rear corners and 100 feet
behind and ahead of the vehicle.

A vehicle inspection should be done before, during, and after a trip. After
the trip, day, or tour of duty, you should fill out a report listing any problems you
found. During a trip, you should inspect the vehicle within the first 50 miles and
then every 150 miles or 3 hours (whichever comes first)

When doubling your speed, your braking distance is 4 times as long. If
you triple your speed, the braking distance is 9 times as long.

Drivers signalling a turn may be a hazard because they may slow more
than expected or stop suddenly.

When water or slush collects on the road. When this happens, your vehicle can hydroplane. It is like water skiing–the tires lose their contact with the road and have little or no traction. You may not be able to steer or brake. You can regain control by releasing the accelerator and pushing in the clutch. This will slow your vehicle and let the wheels turn freely. If the vehicle is hydroplaning, do not use the brakes to slow down. If the drive wheels start to skid, push in the clutch to let them turn freely.

You must turn your headlights on a half hour after sunset and a half hour
before sunrise; when visibility is not sufficient to clearly see a person or vehicle
for a distance for 1000 feet; and if snow, rain, fog, or other hazardous weather
condition require the use of windshield wipers.

To determine how many seconds of following distance space you have,
wait until a vehicle ahead passes a shadow on the road, a pavement marking, or
some other clear landmark and then count the seconds until you reach the same
spot. There is no need to double the number of seconds.

You need at least 1 second for each 10 feet of vehicle length at speeds
below 40 mph. At speeds greater than 40 mph, add an extra second.

Do not speed up. It is safer to be tailgated at a low speed than a high speed

When going down long, steep downgrade, consider the following factors:
total weight of vehicle and cargo, length of grade, steepness of grade, road
conditions, and weather

When backing a vehicle, back towards the driver’s side so you can see better.

The act of operating a motor vehicle in a selfish, bold, or pushy manner,
without regard for the rights and safety of others is called aggressive driving.
The act of operating a motor vehicle with the intent of doing harm to others or
physically assaulting a driver or their vehicle is called road rage.

The total stopping distance is perception distance plus reaction distance
plus braking distance. Perception distance is the distance a vehicle travels from
the time your eyes sees a hazard until your brain recognizes it. Reaction distance
is the distance a vehicle travels before you physically hit the brakes in response
to a hazard seen. Braking distance is the distance a vehicle travels while you are
braking

Driving with wet brakes can cause lack of braking power, wheel
lockups, pulling to one side, and jackknife if you pull a trailer

Stopping is not always the safest thing to do in an emergency. When you
do not have enough room to stop, you should steer away from the hazard ahead.

You should look ahead 12 to 15 seconds; this does not mean you
shouldn’t pay attention to things that are near. You need to shift your attention
back and forth, near and far.

If an oncoming driver has drifted into your lane, a move to your right is
your best bet. If that driver realizes what has happened, the natural response is
for them to return to their own lane. Also, no one is likely to be driving on the
shoulder, but someone may be passing on the left

Never remove the radiator cap or any part of a pressurized system until
the system has cooled. If you can touch the part with your bare hands, it is
probably cool enough to open.

Warning devices for parked vehicles (3 red reflective warning triangles, 6
fuses, or 3 liquid burning flares).

All of the above are ways to prevent a vehicle from rolling back when
stopped on a hill.

You should shift your transmission to a low gear before starting a
downgrade. Do not try to downshift after your speed has already built up. You
will not be able to shift into a lower gear.