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Colorado CDL General Knowledge study materials
Colorado CDL General Knowledge study resources

Colorado CDL General Knowledge practice questions

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Question 1General Knowledge

Under Colorado and federal CDL rules, what minimum blood alcohol concentration (BAC) makes it unlawful for a holder of a commercial driver license to operate a commercial motor vehicle?

  1. 0.02 percent
  2. 0.10 percent
  3. 0.08 percent
  4. 0.04 percent Correct answer.

Explanation

A CDL holder is held to a stricter standard than other drivers: 0.04 percent BAC while operating a commercial motor vehicle is already a violation. The 0.08 percent threshold applies to non-commercial drivers, and 0.10 percent is an older, higher threshold that no longer defines the offense.

Question 2General Knowledge

What is the first action a driver should take when a front tire blows out at highway speed?

  1. Turn the wheel sharply away from the blowout
  2. Brake firmly and steer toward the shoulder
  3. Hold the steering wheel firmly and keep the vehicle straight Correct answer.
  4. Accelerate briefly to stabilize the vehicle

Explanation

A blowout pulls the vehicle toward the failed tire, so the driver must grip the wheel with both hands and keep the vehicle traveling straight before gradually slowing. Hard braking or sharp steering at speed can cause a loss of control or a rollover.

Question 3General Knowledge

When driving a vehicle with air brakes, how can a driver check that the air pressure warning signal is working?

  1. Pump the brake pedal until the warning light comes on Correct answer.
  2. Press the brake pedal and hold it while the engine idles
  3. Turn on the engine and listen for the low-air warning buzzer
  4. Release the parking brake and watch the gauge drop

Explanation

The warning signal must activate before pressure drops below a safe level, so the standard check is to build normal pressure, shut off the engine, and pump the brake pedal while watching for the warning to come on. This confirms the low-air warning device actually functions.

Question 4General Knowledge

A commercial motor vehicle is traveling at 55 mph. Which statement best describes the stopping distance compared with a passenger car?

  1. It is shorter because air brakes apply more force
  2. It is much longer, largely because of the vehicle's weight Correct answer.
  3. It depends only on the driver's reaction time
  4. It is roughly the same if the brakes are in good condition

Explanation

Stopping distance grows sharply with weight and speed, so a loaded CMV at 55 mph needs substantially more roadway than a passenger car. Brake condition matters, but it cannot offset the momentum of a heavy vehicle.

Question 5General Knowledge

Which of the following is the correct way to use a fire extinguisher on a small vehicle fire?

  1. Stand close and aim at the center of the smoke
  2. Aim at the flames and sweep side to side
  3. Spray from the top down and let the chemical settle
  4. Aim at the base of the fire and sweep side to side Correct answer.

Explanation

The extinguishing agent must reach the fuel, so the nozzle is aimed at the base of the fire and swept across it. Aiming at flames or smoke wastes the agent and lets the fire spread.

Question 6General Knowledge

A driver must check the load securement before driving. What is the primary purpose of the required cargo securement system?

  1. To keep the cargo from shifting or falling off the vehicle Correct answer.
  2. To improve fuel economy at highway speed
  3. To make the vehicle easier to unload
  4. To protect the cargo from weather damage

Explanation

Securement systems are required so that cargo cannot shift, slide, or fall from the vehicle, which would create a crash hazard for the driver and other traffic. Weather protection and unloading convenience are not the regulatory purpose.

Question 7General Knowledge

During a pre-trip inspection, what should be checked on the brake system of a vehicle with air brakes?

  1. That the brake lights flash when the pedal is tapped
  2. That the air pressure builds to a normal range and holds Correct answer.
  3. That the parking brake releases quickly
  4. That the brake pedal feels firm at idle

Explanation

The pre-trip check confirms the compressor builds air to the normal operating range and that the system holds pressure when the engine is off. A loss of pressure or a slow build indicates a leak or compressor fault that must be fixed before driving.

Question 8General Knowledge

When backing a tractor-trailer, why should the driver use a helper or spotter whenever possible?

  1. To watch the blind areas the driver cannot see from the cab Correct answer.
  2. To satisfy the requirement that two people be in the cab
  3. To reduce the time needed to complete the maneuver
  4. To keep other drivers from passing behind the trailer

Explanation

Large blind spots behind and beside a trailer make backing dangerous, and a spotter can see hazards the driver cannot. The driver still must check mirrors and use the spotter's signals, but the spotter's main value is visibility.

Question 9General Knowledge

A commercial driver approaches a railroad crossing with a lowered gate and flashing red lights. What is the required action?

  1. Stop and wait until the gate rises and the lights stop flashing Correct answer.
  2. Slow down and cross if the train is far away
  3. Sound the horn and cross quickly
  4. Stop, then proceed if no train is visible

Explanation

A lowered gate and flashing red lights mean a train is approaching, and the driver must stop and remain stopped until the signals clear. A commercial vehicle cannot legally cross against an active warning, even if no train is visible yet.

Question 10General Knowledge

What does the term 'space cushion' mean in commercial driving?

  1. The gap between the tractor and the trailer
  2. The distance a driver keeps from other vehicles and hazards Correct answer.
  3. The area behind the cab reserved for the driver
  4. The distance from the top of the load to the ground

Explanation

A space cushion is the buffer of distance a driver maintains around the vehicle so there is time to react and stop. Managing that buffer in traffic, at intersections, and while following is central to defensive driving.

Question 11General Knowledge

A driver is descending a long, steep downgrade. Which technique is correct for controlling speed?

  1. Use a low gear and the braking system as needed Correct answer.
  2. Shift to neutral and use the brakes lightly
  3. Hold the clutch in and coast
  4. Keep the transmission in high gear and brake hard

Explanation

On a downgrade the driver should select a gear low enough that engine braking helps hold speed, then use the brakes as needed. Coasting in neutral or with the clutch in removes engine braking and can overheat the brakes.

Question 12General Knowledge

What is the purpose of the retarder on a heavy commercial vehicle?

  1. To keep the engine at operating temperature
  2. To lock the trailer brakes when parked
  3. To increase braking force at the wheels during a panic stop
  4. To help slow the vehicle without using the service brakes Correct answer.

Explanation

A retarder, such as an engine or transmission retarder, slows the vehicle on grades and in traffic without relying on the service brakes, which reduces brake heat and fade. It does not replace the service brakes for stopping.

Question 13General Knowledge

A driver's vehicle has hydraulic brakes. What symptom most strongly suggests a brake problem that requires attention before driving?

  1. The brake warning light is off
  2. The pedal feels spongy or sinks when held Correct answer.
  3. The vehicle pulls slightly on a crowned road
  4. The pedal is firm and high

Explanation

A spongy or sinking pedal often indicates air in the hydraulic system or a fluid leak, either of which can cause brake failure. A firm pedal that holds is the normal condition.

Question 14General Knowledge

When must a driver use the four-way flashers on a commercial vehicle?

  1. Only when parking on a shoulder at night
  2. Whenever the driver is unsure of the route
  3. Whenever the vehicle is moving below the speed limit
  4. When the vehicle is stopped or moving slowly and is a hazard to others Correct answer.

Explanation

Four-way flashers warn other drivers that the vehicle is a hazard, typically when stopped or moving unusually slowly, such as on a shoulder or in a work zone. They are not a general signal for normal driving.

Question 15General Knowledge

A driver is about to cross a bridge posted with a weight limit. What should the driver do?

  1. Cross slowly to reduce the load on the bridge
  2. Check the vehicle's gross weight and axle weights against the posted limit Correct answer.
  3. Assume the limit applies only to single-unit trucks
  4. Cross only if the load is evenly distributed

Explanation

Posted bridge limits apply to the actual gross and axle weights of the vehicle, so the driver must know those weights and compare them with the posting. Speed and load distribution do not change the legal weight limit.

Question 16General Knowledge

What is the correct procedure for a driver who must stop on a highway shoulder because of an emergency?

  1. Stop on the shoulder and leave the engine running with lights off
  2. Stop in the right lane and set out flares immediately
  3. Stop in the travel lane with flashers on
  4. Pull as far onto the shoulder as possible and turn on the flashers Correct answer.

Explanation

The vehicle should be moved as far off the travel lane as conditions allow, and the hazard flashers should be turned on to warn approaching traffic. Stopping in a travel lane creates a serious collision risk.

Question 17General Knowledge

When driving at night, what is the main reason a commercial driver should reduce speed below the posted limit?

  1. Visibility is limited to the distance illuminated by the headlights Correct answer.
  2. Other drivers are more likely to honk at night
  3. Headlights are required by law at night
  4. The vehicle's engine runs cooler at lower speed

Explanation

At night the driver can only see as far as the headlights reach, so speed must be low enough to stop within that illuminated distance. Driving faster than the lights allow leaves no room to react to hazards.

Question 18General Knowledge

A driver is following another commercial vehicle on a wet road. What following distance is generally recommended to allow for reduced traction and longer stopping distance?

  1. Exactly two seconds regardless of conditions
  2. One second for each 10 feet of vehicle length Correct answer.
  3. As close as possible to draft behind the lead vehicle
  4. At least one second behind the vehicle

Explanation

The standard rule is to allow one second of following distance for each 10 feet of vehicle length, and to add more time in poor weather or when heavily loaded. Wet pavement lengthens stopping distance, so extra space is needed.

Question 19General Knowledge

A driver's vehicle begins to skid on an icy road. What should the driver do?

  1. Turn the wheel sharply opposite the skid
  2. Brake hard and steer into the skid
  3. Accelerate to regain traction
  4. Release the brakes and steer in the direction the vehicle should go Correct answer.

Explanation

Releasing the brakes lets the tires regain grip, and steering where the driver wants the vehicle to go helps recover from the skid. Hard braking or sharp counter-steering can worsen the loss of control.

Question 20General Knowledge

What does a driver need to remember about the 'blind spot' on a large commercial vehicle?

  1. It disappears when the mirrors are properly adjusted
  2. It exists on both sides and behind the vehicle, and can hide other vehicles Correct answer.
  3. It only matters when the vehicle is backing
  4. It is limited to the area directly behind the trailer

Explanation

Large vehicles have blind spots on both sides and behind, and mirrors cannot eliminate them entirely. Drivers must check mirrors carefully and be aware that other vehicles can disappear from view in those areas.

Question 21General Knowledge

A driver is hauling a load that extends beyond the rear of the vehicle. What is required during daylight hours?

  1. A flashing light at the end of the load
  2. No marking if the overhang is under 6 feet
  3. A white flag at the front of the vehicle
  4. A red flag at least 18 inches square at the end of the load Correct answer.

Explanation

An overhanging load must be marked so other drivers can see its extent; during daylight a red flag at least 18 inches square is the standard warning. At night, a red light or reflector is used instead.

Question 22General Knowledge

When should a driver downshift before entering a curve or turn?

  1. After entering the curve and feeling the vehicle slow
  2. Before the curve, so the vehicle is at a safe speed when it enters Correct answer.
  3. Only if the vehicle is empty
  4. While braking hard in the middle of the curve

Explanation

Speed should be reduced and the correct gear selected before the curve so the driver can maintain control without braking hard while turning. Braking or shifting mid-curve can cause a skid or loss of control.

Question 23General Knowledge

What is the main hazard of overloading a commercial vehicle beyond its rated capacity?

  1. It can overload tires and brakes and lengthen stopping distance Correct answer.
  2. It reduces the need for load securement
  3. It improves traction on wet roads
  4. It increases fuel economy

Explanation

Excess weight stresses tires, brakes, and suspension and increases stopping distance, which raises the risk of a crash. Overloading also violates weight laws and can damage the vehicle.

Question 24General Knowledge

A driver must respond to a tire fire on the vehicle. Which action is appropriate?

  1. Continue driving to the nearest station to save time
  2. Open the hood to look for the source of the fire
  3. Pour water on the fuel tank to cool it
  4. Stop, get passengers or others away, and use an extinguisher if safe Correct answer.

Explanation

The driver should stop safely, move people away from the vehicle, and use a fire extinguisher only if the fire is small and it is safe to do so. Continuing to drive or opening components can spread the fire or cause injury.

Question 25General Knowledge

What is the purpose of the engine brake or 'jake brake' on a heavy truck?

  1. To keep the transmission cool
  2. To help slow the vehicle by using engine compression Correct answer.
  3. To start the engine in cold weather
  4. To increase engine power on grades

Explanation

An engine brake uses the engine's compression to resist motion and slow the vehicle, which reduces reliance on the service brakes on long downgrades. It does not add power or start the engine.

Question 26General Knowledge

Under Colorado's CDL rules, a driver must report a conviction for a serious traffic violation to the employer within how many days of the conviction?

  1. 30 days
  2. 7 days Correct answer.
  3. By the next business day
  4. 24 hours

Explanation

A CDL holder must notify the employer in writing within 30 days of any conviction for a traffic violation, other than a parking violation, committed in any type of motor vehicle. For serious traffic violations the requirement is tighter: the driver must notify the employer within 7 calendar days.

Question 27General Knowledge

A driver holds a Class A CDL and is driving a vehicle carrying hazardous materials that requires placards. Which requirement applies?

  1. No endorsement as long as the load is under 1,000 pounds
  2. A commercial learner's permit with a passenger endorsement
  3. A current federal hazardous materials endorsement on the CDL Correct answer.
  4. A Colorado-only permit issued by the State Patrol

Explanation

Driving a vehicle that requires hazardous materials placards requires the hazmat endorsement on the CDL, which involves a TSA security threat assessment and a knowledge test. Vehicle weight or state boundaries do not remove this requirement.

Question 28General Knowledge

A CMV driver is involved in a crash in Colorado in which a person is injured. Which action does the law require?

  1. Report the crash only if damage exceeds $1,000
  2. Leave the scene only after exchanging insurance cards
  3. Continue to the nearest terminal and report the crash there
  4. Stop, render aid, and remain until reporting duties are met Correct answer.

Explanation

Any driver involved in a crash resulting in injury must stop immediately, give reasonable assistance, and remain at the scene until required identification and reporting steps are completed. Leaving the scene of an injury crash is a serious offense.

Question 29General Knowledge

When a driver activates the parking brakes on a vehicle with air brakes, what happens if the air pressure is very low?

  1. The parking brakes stay applied because of spring pressure Correct answer.
  2. The brakes lock only if the engine is running
  3. The service brakes take over automatically
  4. The parking brakes release and the vehicle rolls

Explanation

Spring brakes are held applied by heavy mechanical springs and are pushed off by air pressure. If air pressure drops too low, the springs apply the brakes, which is why a vehicle with a severe air loss will not roll freely.

Question 30General Knowledge

What is the effect of a front-wheel brake limiting valve on a vehicle with air brakes?

  1. It increases front brake pressure for shorter stops
  2. It disables the front brakes entirely below 20 mph
  3. It reduces front braking force to help prevent wheel lockup on slippery roads Correct answer.
  4. It balances air pressure between the trailer and the tractor

Explanation

The limiting valve, often labeled 'slippery' and 'normal,' cuts front brake application pressure to reduce the chance of front wheel lockup and loss of steering on wet or icy pavement. It does not disable the front brakes.

Question 31General Knowledge

During the pre-trip inspection, the driver should check the slack adjusters on a vehicle with air brakes. What is the concern?

  1. Slack adjusters control the trailer electrical connection
  2. Worn adjusters increase tire pressure
  3. Excessive free play indicates the brakes may be out of adjustment Correct answer.
  4. Loose slack adjusters cause the air compressor to run constantly

Explanation

Slack adjusters transfer pushrod force to the brake shoes; too much pushrod travel or free play means the brakes are out of adjustment and stopping power is reduced. Automatic adjusters should keep travel within limits, and manual ones must be checked.

Question 32General Knowledge

A driver is inspecting a coupling and wants to confirm the trailer is properly connected to the tractor. Which check is most reliable?

  1. Listening for the air dryer to cycle
  2. Pulling the tractor forward with the trailer brakes set Correct answer.
  3. Checking that the fifth wheel jaws are closed around the kingpin
  4. Looking for a gap between the apron and the fifth wheel

Explanation

The pull test is the definitive check: with the trailer parking brakes set, gently pull against them and confirm the trailer does not move and the tractor does not separate. Visual checks of the jaws help but cannot confirm a locked coupling.

Question 33General Knowledge

A driver is preparing to drive with a trailer that has a spring brake system. Before moving, the driver should confirm that the trailer air supply valve is in which position?

  1. Pushed in, so the trailer brakes are released and can be charged Correct answer.
  2. Any position, because the valve resets automatically
  3. Pulled out, so the trailer brakes are applied
  4. In the middle position, so the brakes are partly released

Explanation

The trailer air supply valve must be pushed in to charge the trailer system and release the trailer spring brakes so the vehicle can move. Pulling it out applies the trailer brakes and is used for parking or emergencies.

Question 34General Knowledge

A driver is hauling a load of pipe and must secure it. Which principle applies to the cargo securement rules?

  1. Tiedowns only need to be checked at the start of the trip
  2. Rope is preferred over chain for heavy pipe
  3. One tie-down is enough if the pipe is heavy
  4. The aggregate working load limit of the tiedowns must meet the required minimum Correct answer.

Explanation

Cargo securement rules require the total strength of the tiedowns, measured by their aggregate working load limit, to meet or exceed a minimum tied to the cargo weight and length. The system must also be checked during the trip.

Question 35General Knowledge

A driver's vehicle has a placarded quantity of a corrosive material. What does the placard tell an emergency responder?

  1. The route the vehicle is taking
  2. The general hazard class of the material Correct answer.
  3. The driver's home terminal
  4. The exact weight of the shipment

Explanation

Placards communicate the hazard class and division of the material so responders can choose the right protective actions and tactics. They do not convey shipment weight, routing, or carrier details.

Question 36General Knowledge

A driver is approaching a curve on a two-lane highway and wants to use the correct lane position. What should the driver do?

  1. Hug the inside edge to shorten the path
  2. Drive in the center of the lane at all times
  3. Move toward the outside of the curve before entering and then track through Correct answer.
  4. Stay close to the center line throughout the curve

Explanation

For a right-hand curve, a driver should approach from the outside of the lane and then move through the curve, which reduces the effect of centrifugal force and keeps the vehicle from drifting into the other lane. The idea is to smooth the path, not to cut corners.

Question 37General Knowledge

A driver must turn a long tractor-trailer right at an intersection. What is the correct technique?

  1. Turn from the left lane to make a wide swing
  2. Turn wide enough to keep the rear wheels from off-tracking over the curb Correct answer.
  3. Turn sharply to stay in the right lane
  4. Back up if the turn is too tight

Explanation

The rear wheels of a long trailer track inside the path of the front wheels, so a right turn must be set up wide enough to keep the trailer off the curb and out of the adjacent lane. Swinging left first must be done only when it is legal and safe.

Question 38General Knowledge

A driver is driving at highway speed in rain and the tires begin to hydroplane. What is the correct response?

  1. Release the accelerator and steer straight until traction returns Correct answer.
  2. Accelerate to push through the water
  3. Turn the wheel sharply to test for grip
  4. Brake firmly and steer toward the shoulder

Explanation

Hydroplaning means the tires are riding on a film of water with little or no contact with the road. Easing off the accelerator and holding a straight course lets the vehicle slow gradually until the tires regain contact; hard braking or steering can cause a skid.

Question 39General Knowledge

What is the main reason a driver should avoid using the engine brake in a residential area or where signs prohibit it?

  1. It creates loud noise that may violate local ordinances Correct answer.
  2. It causes the transmission to overheat
  3. It disables the service brakes
  4. It increases fuel consumption noticeably

Explanation

Engine brakes produce a loud, distinctive noise, and many communities restrict their use to control sound. Drivers should watch for signs and follow local rules even where the brake would otherwise help control speed.

Question 40General Knowledge

A driver's vehicle has a malfunctioning speedometer. What does this mean for the driver under the CDL rules?

  1. The driver may continue if the trip is under 50 miles
  2. The vehicle is out of service until the speedometer is repaired Correct answer.
  3. The driver may use a GPS speed display instead
  4. The vehicle may be driven if the driver estimates speed

Explanation

A CMV must have a functioning speedometer; a defective one is a safety defect that places the vehicle out of service until it is repaired. Estimating speed or substituting another display does not satisfy the requirement.

Question 41Air Brakes

On a Colorado CDL air brake pre-trip inspection, the low air pressure warning must activate before the pressure in the system drops below what value?

  1. 60 psi Correct answer.
  2. 45 psi
  3. 75 psi
  4. 30 psi

Explanation

Federal air brake standards require a visible or audible warning to activate before system pressure falls below 60 psi. During the pre-trip test you build pressure, then pump the brake to reduce it and confirm the warning comes on at or above that threshold.

Question 42Air Brakes

The governor on an air-brake-equipped vehicle serves which purpose?

  1. It controls when the compressor cuts in and out to maintain system pressure Correct answer.
  2. It drains moisture from the supply reservoir each cycle
  3. It limits the maximum application pressure at the brake chambers
  4. It balances air pressure between the primary and secondary circuits

Explanation

The governor senses reservoir pressure and cycles the compressor, engaging it at the cut-in pressure and disengaging it at the cut-out pressure. This keeps the system within its designed operating range instead of letting the compressor run continuously.

Question 43Air Brakes

What is the purpose of the slack adjusters in an air brake system?

  1. They prevent the wheels from locking during hard braking
  2. They release air from the chambers after each stop
  3. They keep the brake shoes adjusted as the linings wear Correct answer.
  4. They regulate how fast pressure builds in the reservoirs

Explanation

Slack adjusters connect the push rod to the brake chamber and take up the clearance created as lining material wears away. Without proper adjustment, push rod travel becomes excessive and braking force is reduced.

Question 44Air Brakes

During a pre-trip inspection you apply the brakes and hear a steady hiss that continues while the pedal is held down. What does this most likely indicate?

  1. Normal operation of the relay valve
  2. An air leak in the brake system Correct answer.
  3. The compressor building pressure
  4. The low pressure warning activating

Explanation

A continuous hiss while the brakes are applied and held points to a leak somewhere in the applied circuit, such as a hose, fitting, or chamber diaphragm. Normal brake application produces only a brief release of air when the pedal is let up, not a sustained hiss.

Question 45Air Brakes

In a dual air brake system, the two separate circuits are provided mainly to do what?

  1. Increase total braking force at the wheels
  2. Allow the trailer to be charged faster
  3. Provide a backup if one circuit loses pressure Correct answer.
  4. Reduce the amount of compressor run time

Explanation

Dual circuits isolate the front and rear (or tractor and trailer) braking so that a failure in one circuit still leaves the other able to stop the vehicle. This redundancy is why a single leak does not leave the truck with no brakes at all.

Question 46Air Brakes

Spring brakes on a heavy vehicle will begin to apply automatically when system air pressure falls to approximately what range?

  1. 85 to 75 psi
  2. 20 to 40 psi
  3. 60 to 45 psi Correct answer.
  4. 100 to 90 psi

Explanation

Spring brakes are held off by air pressure; as pressure falls to roughly 45 psi and below, the springs overcome the remaining air and start to apply the brakes. This is why the low pressure warning must sound well before that point.

Question 47Air Brakes

You are driving a truck with air brakes and the pressure gauge shows a steady drop while you are not using the brakes. What is the safest immediate action?

  1. Pump the brake pedal to rebuild pressure
  2. Increase engine speed to help the compressor
  3. Stop in a safe place and check for leaks Correct answer.
  4. Continue driving but shift to a lower gear

Explanation

Pressure that falls without brake use means the system is leaking faster than it can be replenished, and braking performance could be lost. The safe response is to stop in a safe location and inspect for the leak before continuing.

Question 48Air Brakes

When checking push rod travel on a brake chamber with the brakes applied, why is the measurement important?

  1. It indicates whether the slack adjuster is properly adjusted Correct answer.
  2. It verifies the low pressure warning works
  3. It shows whether the chamber diaphragm is torn
  4. It confirms the compressor cut-out pressure

Explanation

Excessive push rod travel means the slack adjuster is out of adjustment and the brake chamber cannot deliver full force to the shoe. Measuring travel against the limit for that chamber type is the standard way to confirm adjustment.

Question 49Air Brakes

What does the air dryer do in a CDL vehicle's air brake system?

  1. It cools the compressor during long downgrades
  2. It regulates the pressure sent to the trailer
  3. It removes moisture and contaminants from the compressed air Correct answer.
  4. It stores extra air for emergency braking

Explanation

The air dryer traps water vapor and oil before the air reaches the reservoirs, which helps prevent corrosion and freeze-ups in the lines. Its cartridge must be serviced according to the manufacturer's schedule.

Question 50Air Brakes

A driver must make an emergency stop and the service brakes fail to hold pressure. What provides the final means of stopping the vehicle?

  1. The parking brake lever only
  2. The spring brakes applying as pressure bleeds off Correct answer.
  3. The transmission retarder
  4. The trailer hand valve

Explanation

Spring brakes are designed to apply automatically when air pressure is lost, giving a fail-safe stopping force. This is why they are also called emergency brakes in addition to parking brakes.