Maryland CDL General Knowledge common mistakes
Maryland CDL General Knowledge · Understand the traps and how to avoid them.
Treating the pre-trip inspection as a memorized recital: reciting 'lights, tires, brakes' in a fixed chant without physically pointing to and naming each component, its condition, and what a defect would look like, so the examiner marks the item as not checked.
Candidates practice the inspection as a speech rather than as a walk-around procedure, often studying from a list instead of performing it on an actual vehicle. Under test pressure they skip items they cannot see clearly (brake chambers, slack adjusters, fifth wheel jaws) and hope the examiner does not notice.
What to do instead
Practice on a real vehicle with a partner holding the Maryland skills-test checklist. For every item say three things out loud: the name of the part, its required condition, and the defect you are ruling out (for example, 'slack adjuster, not more than about one inch of play when pulled by hand, checking for a broken or frozen adjuster'). Time yourself so the full inspection fits the test window, and repeat until you can do it without the list.
Answering air brake questions from everyday driving intuition instead of system logic: assuming the parking brake is applied by air pressure, that a low-pressure warning comes on only after the brakes fail, or that the safety valve and the governor do the same job.
Air brakes are a spring-and-air system with fail-safe design, and candidates who have only driven hydraulic-brake cars map the wrong mental model onto it. The 'spring brakes apply when air is lost' idea is counterintuitive and gets flipped under exam pressure.
What to do instead
Learn the system as a chain: compressor, governor, reservoirs, foot valve, brake chambers, slack adjusters, and spring brakes held off by air pressure. Draw the chain from memory and label what happens at each point when pressure drops. Memorize the key numbers Maryland tests: the low-air warning must activate by 60 psi, the spring brakes must apply between 20 and 45 psi, and the system must hold pressure with the engine off. Then explain the static leak-down test out loud until the logic, not the wording, is what you remember.
Coupling and uncoupling combination vehicles in the wrong order, or skipping the tug test and the visual check of the fifth wheel jaws, and answering questions about the sequence by guessing.
The sequence has many steps and candidates learn it as a paragraph rather than as a checklist. The two steps that actually catch a bad coupling, the tug test and the visual check that the jaws are closed around the kingpin, are the ones most often dropped because they feel redundant after the trailer seems attached.
What to do instead
Write the coupling sequence as numbered steps and rehearse it on a vehicle: inspect the fifth wheel and kingpin, check the trailer height so the tractor is not too high or too low, back until the jaws close, tug test twice, visually check the jaws and the release handle, connect the air lines and electrical cord, raise the landing gear, and check the trailer brakes. Learn the uncoupling order as its reverse, ending with the tractor pulled clear. Be able to state why each step exists, since exam items ask what happens if a step is skipped.
Backing and turning a long vehicle using car habits: backing on the mirrors alone without getting out to look, turning the wheel the wrong way when the trailer appears in the mirror, or swinging wide into the wrong lane on a right turn.
In a car the rear follows the front closely; with a trailer the rear of the trailer swings opposite the tractor's steer tires. Candidates watch the trailer in the mirror and steer toward the danger. Right turns are misjudged because the rear wheels track inside the front wheels, and candidates forget the trailer off-tracks even further.
What to do instead
Learn the rule that the top of the steering wheel moves the bottom of the trailer: to move the trailer's rear left, turn the wheel right. Practice in an empty lot with cones, using both mirrors and a spotter, and get out to look whenever unsure. For right turns, drive past the corner before turning, swing wide only into your own lane, and check both mirrors through the turn for the trailer's rear wheels. Know the off-tracking rule: the longer the wheelbase and trailer, the more the rear wheels cut inside the front path.
Managing space by following distance alone, ignoring the total stopping distance stack and the effect of speed, load, and road surface, and answering 'following distance' questions with a single fixed number of car lengths.
Candidates memorize 'one second per ten feet' or 'four seconds' without understanding that perception distance, reaction distance, brake lag, and braking distance add up, and that air brakes add lag that hydraulic brakes do not have. Load weight and downgrades change stopping distance, so a single number feels safe but is wrong in context.
What to do instead
Build the stack explicitly: perception distance plus reaction distance plus brake lag plus braking distance equals total stopping distance, and be able to say which parts grow with speed and which with weight or grade. Practice the four-second following rule at highway speed and add a second for rain, a second for darkness, and more for ice or a heavy load. For downgrades, know the rule to select a gear before the descent that holds speed without riding the brakes, and to use the same gear coming down that you used going up.
Handling railroad crossings and hazard perception as trivia: rolling through a crossing without checking that the trailer will clear, stopping on the tracks because traffic ahead is backed up, or failing to identify a stale green light or a hidden hazard in a written scenario.
Candidates treat crossings as a formality because they have crossed thousands of them in cars, and they underestimate how long a long combination takes to clear. Scenario questions are missed because candidates answer from the first detail they notice rather than scanning the whole scene for the developing hazard.
What to do instead
Adopt a fixed crossing routine: slow down, look and listen, open the window if needed, check that there is room on the far side for the entire vehicle including the trailer, and never start across until you can clear. Know that a bus carrying passengers must stop at crossings. For hazard perception items, practice the scan pattern: look far ahead, check mirrors, look at the sides and intersections, and name the hazard and the action you would take before reading the options.
Missing the emergency-procedure items that differ from car driving: pumping the brakes after a tire blowout, steering hard against a skid, using the trailer hand valve for parking, or not knowing how to stop a vehicle with a stuck accelerator.
These situations are rare in real driving and candidates have no physical memory of them, so they answer with car instincts or with guesses. The trailer hand valve is a common trap because it looks like a parking brake but is only for testing trailer brakes.
What to do instead
Learn each emergency as a short script. Blowout: hold the wheel firmly, stay off the brakes, ease off the accelerator, and let the vehicle slow before braking gently. Skid: stop braking, turn in the direction you want to go, and do not oversteer. Stuck accelerator: shift to neutral, brake, and pull off the road. Stuck in a dangerous place with a runaway: use the escape ramp. Never use the trailer hand valve for parking; use the spring brakes. Rehearse each script aloud until it is automatic.
Loading and securing cargo by feel: assuming 'it looks heavy enough to stay put', using the wrong number of tiedowns, or forgetting that the aggregate working load limit must be at least half the cargo weight.
Candidates have loaded pickups and trailers casually and never calculated a working load limit. The regulation is numerical rather than intuitive, and the difference between the cargo weight and the aggregate working load limit is easy to blur under exam pressure.
What to do instead
Memorize the core securement rules and be able to apply them to a described load: cargo must be secured so it cannot shift, the aggregate working load limit of the tiedowns must be at least half the weight of the cargo, and the number of tiedowns depends on the length and weight of the article. Know that the front end of a load must be against the headboard or secured to prevent forward movement, and that covers and tarps need their own securement. Practice with two or three sample loads, calculating tiedown count and working load limit each time.
Treating hazardous materials placarding and shipping papers as general knowledge: guessing when a placard is required, confusing the hazard class numbers, or not knowing who is responsible for the shipping paper and what it must contain.
The placarding thresholds and the split of responsibility between shipper and carrier are administrative details that candidates skip because they seem less exciting than driving skills. Class numbers and division names are easy to half-learn, and a half-learned number looks right on a multiple-choice item.
What to do instead
Learn the nine hazard classes and their names as a table, then learn the placarding rule: placards are required for 1,001 pounds or more of an aggregate gross weight of a hazardous material in one class, and for any amount of certain materials such as poison inhalation hazards and dangerous when wet. Know that the shipper prepares the shipping paper and the carrier may not accept a shipment without it, and that the shipping paper must be within reach of the driver, kept in the same place, and available to emergency responders. Also know the emergency response information and the emergency response telephone number requirements.
Skipping the endorsement-specific rules that do not appear in general driving: for passengers, forgetting that a bus must stop at railroad crossings and that standees are limited; for tankers, not knowing about baffles, surge, and the smooth-bore versus baffled difference; for doubles and triples, not knowing converter dollies and the check that the rear trailer is tracking properly.
Candidates study the general knowledge manual and assume the endorsement sections repeat it, so they never read the sections on passenger transport, tankers, or doubles and triples. Each endorsement has its own vocabulary and its own test items, and the general material does not cover them.
What to do instead
Read each endorsement section separately and make a one-page sheet of rules unique to it. For passengers: stop at all railroad crossings, never allow standees to block the aisle or stand forward of the driver, and know the rules on loading and unloading at stops. For tankers: understand baffles and why they reduce but do not eliminate surge, and know that smooth-bore tanks have more liquid surge and require gentler starts and stops. For doubles and triples: know the converter dolly, the order of coupling and uncoupling, and the need to check that the rear trailer is tracking in line. Then take practice items for each endorsement separately so the vocabulary sticks.