FREE 2025 CDL Practice Test

You must drain the air tanks completely at the end of each working day to avoid buildup of moisture and oil. If enough moisture is collected, the water can freeze and cause brake failure.

There are two types: manual and automatic air tank drains. If your vehicle has automatic air tank drains, the water and oil will be automatically expelled. If you vehicle has manual air tank drains, you have to drain the tank using the manual draining valve located in the bottom of the tank.

If your vehicle has manual slack adjustors, the brake pushrod should move less than 1 inch when pulled by hand with the brakes released.

The static leakage test is done by charging the air system fully, then turning the engine off and releasing all the brakes. In 1 minute, the air pressure should drop no more than 2 psi for single vehicle, 3 psi for a combination of 2 vehicles, or 5 for a combination of 3 or more vehicles.

Any loss greater than the above mentioned indicates a problem in the braking system.

The ABS will automatically activate during emergency braking to prevent your wheels from locking up. As the wheels don’t lock, you can steer while braking - which is especially beneficial if you need to steer to avoid something. ABS won't affect the way you drive or affect the stopping or braking distance, but it will help you control the vehicle. All truck tractors with air brakes built after March 1997 must be equipped with air brakes.

Air brakes rely on compressed air to flow through the lines and fill up the brake chamber up to a certain air pressure for the brakes to work.

The emergency/supply line is used for 2 main purposes: to supply air to the trailer air tanks and to control the emergency brakes on combination vehicles. A loss of air pressure in the emergency line will lead to the emergency brakes, which are usually spring brakes, coming on. An example of when the emergency line could lose air pressure is when a trailer breaks loose and rips up the emergency line - in this situation the emergency spring brakes will automatically activate to slow the trailer down.

To help keep the different air lines apart, service lines are often coded blue and emergency lines red.

The service line is used to supply air to the air brakes on combination vehicles, and these brakes are controlled by the foot brake or trailer hand brake. It is connected to the relay valves which allow the trailer brakes to be applied more quickly. It's the emergency line that controls the emergency brakes, not the service line.

The shut-off valves are used to close the air lines at the back of a trailer if another trailer is not being towed. This allows air pressure to build within the system and not leak out at the back. The shut-off valves should be in the open position on all trailers except the one at the back where it must be closed.

After the fifth wheel has been unlocked, you need to first partially move the tractor to ensure that the trailer can support itself. You do this by moving the tractor forward until the fifth-wheel is clear of the trailer, but not the tractor frame. You want to keep the tractor frame under the trailer in case the landing gear fails due to the ground not being solid enough or damage to the landing gear itself. Only after you have checked to make sure the landing gear can support the trailer should the tractor be moved out completely.

As you unlock the fifth-wheel, you want to position yourself away from the rear tractor wheels in case it moves.

You test the brakes on double or triple trailers the same as you would on any other combination vehicle

A visual check of the coupling is very important as you'll immediately see if something is wrong. If the coupling is correct, there should be no visible space between the upper and lower fifth-wheel, and the locking jaws should have closed around the kingpin. You can test the coupling by pulling against the pin of the second semitrailer.

The locking jaws should be around the shank, not the head of the kingpin. The fifth-wheel should be securely mounted, have no damaged or missing parts, and be greased. There should be no visible space between the lower and upper fifth-wheel. The safety latch must be engaged and the release arm properly placed.

There is no exact distance between the fifth-wheel and the tractor frame, but you need to make sure they are far enough apart so neither the tractor frame hits the landing gear during turns, nor the cab hits the trailer during turns.

To ensure the safest handling on the road, you will want to place the most heavily loaded semitrailer closest to the tractor, and the lightest trailer in the rear. This will distribute the braking and turning force most evenly across all the wheels and prevent over / understeering.

Drivers can make a fire worse by not following the proper procedures in case of fire. If there is an isolated fire within a van or box trailer, pull off the road and notify emergency services. As the fire is isolated, you don't want to open the van doors and let oxygen in (more oxygen will cause the fire to burn faster). Instead, keep the fire from spreading beyond the van or box trailer and wait for the emergency services to arrive.

Some fires, such as HazMat fires, require special fire extinguishers capable of extinguishing that particular class of fire. Read the label on the fire extinguisher before using it.

While additional weight will impact the stopping distance on most vehicles negatively, the braking system in a truck is designed to work best and give the most traction when the vehicle is fully loaded. This means most empty trucks take longer to stop than when fully loaded.

The best way to make the roads a safer place is by being aware of the road rules, staying focused, signaling your intentions, and driving defensively.

The stopping distance increases in bad weather, so drive slower than you would in ideal conditions and increase the following distance. In general, wet roads can double the stopping distance. Adjust to this by reducing your speed by at least 1/3 on a wet road, and by even more on a road with snow. If there is ice, your stopping distance may increase by up to 10 times.

Medicines can affect your concentration, coordination, mood, and reactions. The label says ‘do not drive’ for a reason.

Liquids in a cargo tank will expand as the temperature changes during transit. To prevent the tank from becoming too full, every tank carrying liquids has to be empty to some percentage, i.e. the amount of outage or ullage needed. How much outage or ullage that is needed will depend on the liquid being transported, but there must be enough outage so the tank will not be full at 130 degrees Fahrenheit.

Placards for Hazmat may be displayed even if they are not required, but they must identify the hazard of the material in question. The placards must follow the color specifications.

A shipping paper is used to describe the HazMat / materials being transported. It includes bills of lading, manifests and shipping orders. It will show the quantity and hazard class of the materials to provide for easy identification and response in case of an accident.

Do not park on a private property unless the owner is aware of the danger. When the HazMat vehicle is parked, someone has to watch the vehicle. The person watching the vehicle may be someone else only if your vehicle is parked on the shipper's property, the carrier's property or the consignee's property.

In case of a vehicle breakdown, you should only use the reflective triangles and/or red electric lights if transporting a material close to which a fire is prohibited. Examples of such materials include any tank used for transporting Class 3 or Division 2.1 whether loaded or empty, and all vehicles used for transporting explosives.

You should have all emergency equipment as required by law. You don't have to bring spare electrical fuses if the bus is equipped with circuit breakers.

Most bus accidents occur at intersections. Bus driver's must use caution at intersections to avoid accidents, even when other vehicles must yield the right of way.

There is not a set amount of time you should wait before departing as each situation will be different. For example; an old person requires much more time to get into his or her seat than a teen, while also being far more likely to be injured in a fall.

Using regrooved tires on the steer axle is prohibited for any truck or tractor if the load-carrying capacity is greater or equal to 2,232 kg (4,920 pounds). For buses, regrooved, recapped or retreaded tires are prohibited on the front wheels regardless of load-carrying capacity.

The aisle and doorways should be clear of baggage. In an emergency, misplaced bags in the doorways or aisles can be very dangerous as they will make a safe evacuation much harder. Secure bagge and freight in a safe place that does not damage the cargo.

The driver and all riders must be able to use all exits and not have their movement restricted due to bags or freight.

A worn, cracked or old belt may snap as you drive. Engine compartment belts must be in good shape and without more than 3/4 inch play at center of the belt.

Before you do any further inspection of the vehicle, you must make sure the vehicle won't roll or move away. If the vehicle moves during an inspection, you can get serious injuries.

The ammeter/voltmeter gauge should show that the alternator / generator is charging on engine startup, and that the warning light is off.

The draw-bar may reach the wear limit after it has been used for a long time. If the draw-bar shows excessive wear or any damage, it must be replaced. A draw-bar / draw-bar eye should never be repaired, only replaced.

If you damage the draw-bar or draw-bar eye in any way, it has to be replaced. Do not attempt to repair the draw-bar eye or continue using a damaged draw-bar eye. Damage is, for example, any stress cracks, broken welds, or bent or twisted parts.

You want to stop the school bus so the students have to walk 10 feet or more to the bus. This will give you a better view of their movements and lets you monitor if anyone enters a danger zone.

Your outside left and right side flat mirrors have large blind spots immediately below and in front of each mirrors, as well as directly in back of the rear bumper of the school bus. For a regular-sized school bus, the blind spot extends for 50 to 150 feet, but it can extend for up to 400 feet depending on the size of the bus.

In some instances during unloading, you will need to move out of the driver's compartment and position yourself to supervise loading. If you do, always set the parking brake, turn off the ignition, and bring the key with you.

The unloading procedures along the school bus route are often different than the unloading procedures at school. To unload along a route, you need to keep track of the number of students in the bus at all times. By counting the number of students on the bus, and the students leaving, you will be able to monitor their movements and ensure that you can safely locate each student before you move off.

You should ask the unloaded students to move at least 10 feet away from the bus and stand in a position where you can clearly see all students. If you cannot account for a student, you will have to secure the bus and search in, under and around the school bus before you proceed.

School districts will establish official school bus stops and routes. The school bus stops must be approved by the school district before the school bus stops there. You should only change the location of a school bus stop following written approval from a school district official.

Unbaffled tanks have no baffles inside to slow down the flow of the liquid - which means the relative back-to-front surge will be very strong. When driving an unbaffled tank you must be careful as you start or stop to prevent the surge from drastically affecting the vehicle's handling.

The sideways surge is not likely to be affected much as the baffles are used to slow down the back-to-front surge of the liquid.

Baffles will make the tank harder to clean inside. Food products such as milk etc. must be transported in an unbaffled tank because of sanitation regulations.

Baffles and bulkheads are dividers in the tanks. They are used to either reduce the amount of surge that is possible or divide the liquids into several smaller compartment. Bulkheads are solid dividers; baffles are bulkheads with holes to let liquid pass between.

The liquid in a partially filled tank will move as you change speed. For example; the liquid will surge back and forth as you come to a stop, which will have effects on handling.

According to federal regulations, a tank endorsement must be added to your CDL if you intend to transport liquids or gases in a tank having an individual rated capacity of at least 119 gallons and an aggregate rated capacity of at least 1,000 gallons. The tank can be either permanently or temporarily attached to the vehicle or chassis.