Ohio CDL Doubles and Triples Endorsement Test common mistakes
Ohio CDL Doubles and Triples Endorsement Test · Understand the traps and how to avoid them.
When coupling a tractor to a converter dolly, the candidate backs under the dolly and immediately pulls forward without first ensuring the dolly's kingpin is fully engaged and the locking jaws are closed, then the dolly separates on the road test.
Candidates confuse the lighter dolly with a semitrailer and skip the mandatory physical tug test because the dolly is small and seems easy to couple; they also forget that the dolly has its own air lines and electrical cord that must be connected before the pull test.
What to do instead
After backing under the dolly, set the parking brake, get out, and visually confirm the kingpin is seated in the fifth-wheel throat with the locking jaws closed around it. Connect the dolly's air lines and electrical cord, then do a firm tug test against the dolly with the trailer brakes released and the tractor brakes set. Only after the tug test passes should you raise the dolly landing gear and complete the coupling.
During the uncoupling of twin trailers, the candidate lowers the landing gear of the rear trailer before disconnecting the air lines, causing the trailer to drop or the lines to be stretched and damaged.
The candidate follows a memorized sequence for a single semitrailer and does not adjust for the fact that a converter dolly supports the front of the rear trailer; lowering the gear first takes weight off the dolly and can tip it, and disconnecting air lines under pressure causes them to whip.
What to do instead
Before uncoupling, park on level ground, set the tractor and trailer parking brakes, and chock the wheels. Disconnect the air lines and electrical cord from the dolly first, then lower the dolly landing gear to the ground and secure the dolly. Only then lower the rear trailer landing gear, pull the tractor forward slowly, and verify the trailer is stable before releasing the brakes.
The candidate inspects only the tractor and first trailer during the pre-trip inspection, ignoring the second trailer, the converter dolly, and the connections between them, and misses a cracked dolly frame or a missing safety chain.
Candidates are used to single-trailer inspections and treat the extra units as an afterthought; the inspection is timed, so they rush and skip the dolly and rear trailer, assuming they are fine because they were coupled correctly.
What to do instead
Use a systematic walk-around that starts at the tractor and moves rearward unit by unit: tractor, first trailer, converter dolly, second trailer, and third trailer if present. At each unit check the frame, suspension, tires, lights, air lines, electrical cord, safety chains, and the fifth-wheel or pintle hook connection. Specifically inspect the dolly frame for cracks and the safety chains for secure attachment, and confirm the rear trailer's brakes and lights work from the cab.
The candidate checks the air brake system by building pressure only in the tractor and first trailer, then assumes the rear trailer is charged, and fails to notice that the rear trailer's brakes are not releasing or that the emergency line is not connected.
With multiple trailers, the air lines run in series and a single misconnected line can isolate the rear trailer; candidates do not understand that the rear trailer has its own reservoir and that the tractor's gauge may show normal pressure even when the rear trailer is not receiving air.
What to do instead
After coupling all units, build system pressure to governor cut-out, then perform a leak test at the rear-most trailer's reservoir and check that the rear trailer's brakes apply and release when the treadle is pressed and released. Physically trace each air line from the tractor to each trailer to confirm the emergency (supply) and service lines are connected to the correct gladhands, and verify the rear trailer's spring brakes release when the parking brake is released.
When making a right turn with double or triple trailers, the candidate swings too wide or cuts the corner because they steer as if driving a single trailer, and the rear trailer tracks off the road or strikes a curb.
Each additional trailer increases offtracking and the rear trailer cuts a tighter path than the first trailer; candidates underestimate how far the rear-most trailer swings outward on a right turn and how much the first trailer cuts in on a left turn, and they do not allow for the extra length when judging the turn.
What to do instead
Before the turn, check mirrors and signal early, then move to the proper lane position: for a right turn, keep the tractor close to the right edge but not over it, and for a left turn, swing wide enough to keep the first trailer from cutting the corner. Proceed slowly, watching the rear trailer in the mirrors, and remember that the last trailer follows the tightest path. If unsure, stop and pull forward to complete the turn rather than backing up.
The candidate changes lanes or passes without checking that the rear trailer has cleared the other vehicle, because they rely only on the tractor's mirrors and do not account for the blind spot behind the last trailer.
With multiple trailers, the rear-most trailer is far behind the cab and can be hidden in the mirror blind spots; candidates check the mirror once, see the first trailer, and assume the rest of the combination has cleared, when in fact the second or third trailer is still alongside the other vehicle.
What to do instead
Use a systematic mirror check: look at both flat mirrors and both convex mirrors, and account for the extra length by waiting until the entire combination has passed the other vehicle before returning to the lane. Use the trailer's rear lights or a spotter if available, and when in doubt, delay the lane change until you can see the rear trailer's tires in the mirror. Signal early and make the lane change gradually.
The candidate brakes hard on a curve or while the combination is not straight, causing the trailers to jackknife or the rear trailer to swing out and roll over.
Candidates apply the same braking technique they use in a car or single-unit truck, not realizing that with multiple trailers the rear trailer can push the tractor and that hard braking on a curve unloads the tires and causes a jackknife or trailer swing.
What to do instead
Brake early and gently, and always try to brake with the combination straight. Before entering a curve, reduce speed to a safe level so that no braking is needed in the curve. If braking is necessary in a curve, use light, steady pressure and avoid locking the wheels; if the trailer starts to swing, release the brakes and steer in the direction of the skid to regain control.
The candidate connects the converter dolly's air lines to the wrong gladhands (service to emergency) and then cannot release the rear trailer's brakes or experiences a constant air leak.
The gladhands are color-coded (blue for service, red for emergency) but candidates under pressure grab the nearest line and connect them without checking the color or the coupler shape, and they do not understand that the emergency line charges the trailer reservoir while the service line applies the brakes.
What to do instead
Before connecting, identify the blue service line and the red emergency line on both the dolly and the trailer. Connect the emergency (red) line first, then the service (blue) line, and listen for the click of the coupler. After connecting, tug each line to confirm it is locked, and check that the trailer brakes release when the tractor parking brake is released. If the lines are crossed, the trailer brakes will not release and you will hear a continuous leak.
The candidate fails to recognize and correct a trailer sway situation, instead steering sharply or braking hard, which amplifies the sway and leads to a rollover.
Sway in doubles and triples builds quickly and the natural reaction is to steer against it or hit the brakes; candidates do not know that the correct response is to ease off the accelerator and steer straight, and that hard braking or sharp steering can cause the rear trailer to swing out and tip.
What to do instead
If sway begins, ease off the accelerator and hold the steering wheel firmly in a straight line; do not steer sharply or brake hard. If the combination has a hand valve (trailer brake), apply it gently to straighten the trailers. Once the sway is under control, slow down gradually and pull off the road to check the load and connections. If sway is severe, release the accelerator completely and let the combination slow on its own.
The candidate loads the trailers without checking weight distribution and axle limits, placing heavy cargo at the rear of the last trailer or unevenly across the axles, causing the combination to exceed the gross vehicle weight rating or axle weight limits and handle poorly.
Candidates focus on total weight and forget that each axle and each trailer has its own limit, and that the converter dolly adds an axle that must be considered; they also do not understand that weight placed too far back can lighten the steer axle and cause steering problems.
What to do instead
Before loading, know the empty weight of each unit and the gross and axle weight ratings. Distribute cargo evenly, placing heavier items over or slightly ahead of the trailer axles, and never exceed the rating of any axle or tire. After loading, weigh the combination at a certified scale, checking steer, drive, dolly, and trailer axle weights separately, and adjust the load until all weights are within limits and the steer axle is not too light.