NC CDL Combination Vehicles study plan

Explain in writing why a combination vehicle's rollover threshold is lower than a solo tractor's, naming the roles of high center of gravity and rearward amplification of lateral acceleration.

Calculate the speed at which a 55 ft trailer with a 7 ft track width reaches a 0.4 g rollover threshold, and compare it with a 45 ft trailer to show how trailer length changes the tipping speed.

List five driver actions that raise rollover risk (hard steering at speed, off-ramp overspeed, load shift, brake imbalance, evasive lane change) and match each to a preventive habit you will use behind the wheel.

Practice controlled braking on a straight, empty lot or simulator at 30 mph and record stopping distances for a bobtail versus a loaded combination to illustrate the effect of weight on traction.

Define rearward amplification and explain why a 28 ft doubles set amplifies lateral acceleration at the rear trailer more than a 53 ft single trailer does.

Describe how to recover from trailer sway without braking hard or steering abruptly, and state why countersteering too far can trigger a rollover.

Compute off-tracking for a 90-degree turn with a 53 ft trailer using the rule that off-tracking grows roughly with the square of trailer length, and state the swept-path width you must allow.

Diagram the path a 53 ft trailer takes through a right turn, marking the curb-side overhang and the mirror checks needed before and during the turn.

Identify three conditions that worsen off-tracking (tight turn radius, short wheelbase tractor, wet or soft pavement) and state the speed and lane-position adjustment for each.

Perform a full walk-around inspection of a combination vehicle using the seven-step method and check off every coupling point: fifth wheel jaws, kingpin, safety latch, landing gear, air lines, electrical cord, and glad hands.

Demonstrate the tractor-protection (tug) test and the trailer-supply-air test, and explain what each test proves and what a failure looks like.

Trace the path of the service and emergency air lines from tractor to trailer, identify the color coding, and explain what happens if the lines are crossed or chafed.

Inspect landing gear for cracked legs, bent cranks, and missing shoes, and state the correct stowed height and crank position before moving.

Check tire inflation, tread depth, and dual spacing on the trailer axles and record any defect that would put the vehicle out of service.

Write the coupling sequence from memory: inspect, align, back under, listen for the click, tug test, connect lines, raise landing gear, secure the fifth wheel, and check lights.

Explain why the trailer must be chocked and the tractor parking brake set before coupling, and what can happen if the trailer rolls during the procedure.

Demonstrate the uncoupling sequence in order, including lowering the landing gear to firm ground, disconnecting the air lines, and pulling forward slowly to clear the kingpin.

Identify the three most common coupling errors (high hook, missed kingpin, forgotten landing gear) and describe the physical evidence each leaves behind.

Explain the correct procedure to verify the fifth wheel is locked by checking the release handle is in and the safety latch is engaged, and why a visual check alone is insufficient.

Explain how the tractor protection valve and trailer spring brakes interact during a breakaway, and state the pressure at which the valve closes.

Describe the difference between service brakes, parking brakes, and emergency brakes on a trailer, and identify which air line controls each.

Perform a leak-down test on a combination vehicle: build to governor cut-out, hold the pedal, and record the pressure drop per minute against the allowable limit.

Explain how ABS on the tractor and trailer works together, what the dash lamp indicates, and why you should not pump the brakes during an ABS event.

Describe the correct braking technique for a combination vehicle on a long downgrade, including snubbing and gear selection, and explain why continuous light braking can fade the brakes.

Compare pintle hook, fifth wheel, and converter dolly configurations, listing the coupling points and inspection items unique to each.

Explain how to couple and uncouple doubles, including the order of connecting the converter dolly and the checks before moving.

Describe the air line routing on a triple trailer set and explain why the rear trailer's brakes must be tested separately.

Identify the handling differences of doubles and triples, including increased rearward amplification and the need for wider turns and longer following distance.

State the inspection points on a pintle hook: the latch, the cotter pin, the wear on the hook, and the safety chains or cables.

Calculate the load distribution for a tractor-trailer using axle weight limits, and show how moving 1,000 lb of cargo 10 ft changes the weight on the drive tandems.

Explain the relationship between cargo placement, center of gravity, and rollover risk, and state where heavy items should go in a trailer.

List the four cargo securement requirements (aggregate working load limit, tiedown count, attachment points, and protection against shifting) and apply them to a load of steel coils.

Explain how to read a weigh station scale ticket and identify an overweight axle before leaving the yard.

Describe how sliding the fifth wheel or the trailer tandems changes axle weight distribution, and state when each adjustment is appropriate.

Take a full-length practice test covering all seven domains and score at least 85 percent.

Review every missed question and write the correct rule and the reason for the error for each one.

Re-demonstrate the coupling and uncoupling sequences and the pre-trip inspection from memory without notes.

Recompute the rollover and off-tracking problems from weeks 1 and 2 to confirm retention.