General Knowledge Test Study Guide for the CDL

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General Information

Drivers with a Commercial Driver’s License must know and follow certain guidelines to do their job in the safest and most efficient manner. This study guide aims to give a brief synopsis of some of these rules to help drivers do their job in the best way possible.

Note: Please note the special medical information at the end of this study guide before you begin any driving instruction or the testing process.

Vehicle Inspection

Following the same steps every time you inspect your vehicle can help reduce the chances of missing an important safety hazard or defect.

The Seven Step Pre-Trip Inspection Method

Before embarking on any trip, you should always follow the seven-step pre-trip inspection method. Here are the steps included in this method:

Step 1: Vehicle Overview

  1. Note the general condition of the vehicle.
  2. Look for leaks or puddles of fluid under the vehicle.
  3. Check the last written Vehicle Inspection Report (VIR) to see if there were any problems, and if they have been corrected.

Step 2: Check Engine Compartment

  1. Ensure the wheels are chocked or the parking brakes are on.
  2. Check that all engine fluids are at optimal levels.
  3. Search for loose wires, hoses, and belts.
  4. Check for cracked or worn wiring insulation.
  5. Close the engine hood.

Never inspect inside the engine compartment while the engine is running.

Step 3: Start Engine and Inspect Inside the Cab

  1. Set the parking brakes. Put the gear shift in neutral (or “park” if automatic).
  2. Start the engine. Check for strange noises coming from the motor.
  3. Look at the gauges and ensure each is operating within a normal range. (Warning lights and buzzers should extinguish within a few seconds.)
  4. Check to see if any of the controls seem loose or sticky.
  5. Double-check if the truck is equipped with proper safety equipment, such as reflective triangles and a fire extinguisher.
  6. Check windshield. Adjust mirrors.

When starting an engine, the oil pressure gauge should indicate 5 psi (or more) within 3–5 seconds. If oil pressure shows no increase after 5 seconds, shut off the engine. Oil pressure gauge should stabilize above 50 psi within 30 seconds.

Step 4: Turn Off Engine and Check Lights

  1. Set the parking brakes, turn off the engine, and turn on the headlights and 4-way flashers.
  2. Take the key with you as you go to the front of the vehicle.
  3. When you are confident that all lights are operational, go back into the cab of the vehicle, and push the dimmer switch.
  4. Go back to the front of the vehicle to ensure that the high beams work as well.

Step 5: Do Walking Inspection

  1. Turn on your right turn indicators. Start your walk around the vehicle.
  2. Make sure all tires are in good condition and lights are clear of dirt and operating.
  3. The brakes and suspension should be working.
  4. The fuel tank, exhaust system, and transmission should not be leaking.
  5. Ensure that the cargo is properly secured and required signs/placards are properly displayed.
  6. Make certain the rear doors are latched, locked, and sealed.
  7. Check that the license plate is present and secured.
  8. All hatches and toolboxes should be shut and latched. (Shiny patches of metal or streaks of rust are a clear indication that something is loose, rubbing, or moving.)

Step 6: Check Signal Lights

  1. Turn off all previously checked lights and turn on the stop lights and left turn indicators.
  2. Go outside the vehicle (if needed) to ensure that the lights flash the correct color:
    * Signals facing the front of the vehicle should be amber or white.
    * Signals facing the rear of the vehicle should be amber, red, or yellow.
    * Rear backing lights (if equipped) should be white.
  3. Turn off all lights unnecessary for driving.
  4. Finish your trip planning.
  5. Check that you have all needed paperwork.
  6. Secure any loose items in the cab. Fasten your seatbelt.

Step 7: Start the Engine and Check Test for Hydraulic Leaks

  1. Start the engine.
  2. Test the hydraulic brakes (if equipped) by pressing the brake pedal three times, and then holding the pedal for 5 seconds; the pedal should not move.
  3. Move the vehicle forward and apply the parking brake. If the parking brake works, release it and test the service-brake stopping action. Go about 5 miles per hour and firmly push the brake pedal down. If you feel any pulling to one side or any strange sensations in the pedal, you may be having brake trouble. Address these issues before starting your trip.

Note (between steps 6 and 7): It is not part of any DMV test, but It is generally considered good, safe practice to gather everything you will need during your driving shift (placing everything within easy reach) before starting the engine and setting off:

  • glasses
  • sun glasses
  • trip plan
  • pens/pencils
  • maps
  • log book
  • music
  • beverages and snacks

Inspection During the Trip

During your trip, inspect your truck within the first 50 miles—and every 150 miles or every 3 hours (whichever is first). Ensure that your cargo and truck equipment is still secure, your tires are still in good working order, and your brakes are not overheating. While driving, check the operating condition of your vehicle often (instruments, gauges, air pressure, mirrors, check the tires by looking in the mirrors, etc.). After your trip, fill out a Vehicle Inspection Report (VIR) noting anything that may need to be addressed for maintenance or safety.

Other Safety Precautions

It is important to keep yourself and other drivers as safe as possible while driving. Here are several additional practices that are important.

Backing Up the Trailer Safely

Try to avoid backing your trailer whenever possible. If you must back up, back to the driver’s side (left) for optimum visibility. Unlike backing in a straight truck, when you back up a trailer, you turn the wheel in the opposite direction of where you want to go. Drive slowly and use your mirrors. If you start to head in a direction you do not want to go, turn the steering wheel toward that direction to correct the drift.

When in doubt, G.O.A.L. = Get Out And Look.

Even experienced drivers stop what they are doing, open the door, and climb out of the truck—to examine what is behind the trailer or out of sight.

Seeing While You Drive

Because of the length of commercial tractor-trailers, every action you make takes extra time and consideration. While driving, try and look 12–15 seconds ahead of you to ensure that you have enough time to react to topography changes, traffic, and difficult road conditions. Use your mirrors, but do not look at them for too long. Your main focus should always be what is coming up ahead.


Use your turn signals to indicate to other drivers what you intend to do. Put them on well before you make a turn, and do not turn them off until you have completed your turn. If you see a hazard ahead, such as debris in the road—flash your brake lights by lightly tapping your brake pedal. Because of your size, drivers behind you may not be able to see very far ahead of them. Flashing your brake lights helps alert other drivers of possible problems ahead, giving them time to slow down. If you ever have to stop on the side of the road, put out your reflective triangles within 10 minutes of the stop.

Managing Space

Because your vehicle is much bigger than many others on the road, you need more space in front of you for stopping. A good rule of thumb is that you need 1 second for every 10 feet of vehicle length at speeds under 40 miles per hour. If you are traveling faster than 40 miles per hour, add an extra second. For example, a 50-foot truck driving 60 miles per hour would need 6 seconds to stop (5 seconds for vehicle length plus 1 second for going over 40 miles per hour). Of course—if road conditions are slippery or you are on a hill, you may need additional time to stop, so adjust your speed accordingly.

Hint: You will see these numbers on your written CDL test.

Making Turns Safely

If you are turning left, you should have reached the intersection before beginning your turn. When there is more than one turn lane, always take the outside-right lane, instead of the inside-left lane, because you may need to swing right to complete your turn. If you were on the left lane, swinging right would mean you could potentially hit the vehicle next to you. If you are turning right and need to swing wide, try to keep the rear of the vehicle close to the curb so other drivers do not try to pass you on the right.

Dealing with Difficult Road Conditions

Knowing what to do in different types of inclement weather or challenging topography can greatly increase your chances of a safe trip. Be aware that even on hot, sunny days, tar on the roads can rise to the surface, making the road slippery. If you cannot avoid driving in fog, drive cautiously, turn on your low beams, and be prepared to stop. If you are driving in a mountainous area, shift to low gear before descending a hill. Drive slowly enough that you do not constantly have to use your brakes. Using brakes too often causes them to get hot and may result in brake failure. If you are driving through a large puddle, and your brakes get wet, put the transmission in low gear and gently put pressure on the brakes. When you are out of the water, continue to put light pressure on the brakes to heat them up and dry them out.

Important Definitions

Weight Ratings

  • Gross Vehicle Weight (GVW) is the actual weight of a vehicle (straight truck), including its load.

  • Gross Vehicle Weight Rating (GVWR) is the manufacturer’s maximum weight rating (straight truck), including its load.

  • Gross Combination Weight (GCW) is the same as GVW, except it is for a combination vehicle (with a trailer).

  • Gross Combination Weight Rating (GCWR) is the same as GVWR, except it is for a combination vehicle (with a trailer). (Generally 80,000 pounds)

Hours of Service

HOS stands for Hours Of Service. HOS rules limit how many hours a driver can work and/or drive in a single shift. They also regulate the minimum number of rest hours that a driver must be given between working shifts.

Bonus Facts Concerning Tunnels

  • Be prepared to remove sunglasses when entering a tunnel.

  • Expect sudden gusts of wind when exiting a tunnel.

Medical Requirements

To drive a commercial vehicle, you will need to get an approved Medical Examination Report form (MER, formerly called a “medical card”). A medical examiner (usually a doctor) will examine you. Not all doctors are qualified to issued MERs. A special certification process is required.

Primarily, the examiner will check your:

  • vision (with or without glasses),
  • hearing
  • urine sugar (diabetes).


If you have Type 2 diabetes and do not use insulin, you may still qualify for medical certification. With Type 2 diabetes, you might be granted a one year MER (instead of the normal two year MER).


If you have seizures you might not qualify for an MER.


You can apply for an MER exemption from the diabetes, hearing, seizure and vision requirements. If you are granted an exemption, you will be issued a medical waiver (instead of an MER).

To obtain a medical wavier, apply to the Federal Motor Carrier Safety Administration (FMCSA). It can take the FMCSA 6 months to make a determination on an application. The exemption would be valid for primarily interstate (between states) driving.

Some states issue medical waivers. A state-issued medical waiver would be valid for only intrastate (within state) driving.

Plan Ahead

If you think that there is some possibility that you can not qualify for an MER, it’s best to try to get it before you spend time, effort, and money on driving school.

Your driving school can help you through the process of finding an examiner and advise you on MERs and waivers.

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