Georgia CDL Combination Vehicles Test cheat sheet

A combination vehicle is a tractor (or truck) plus one or more trailers; the coupling point (fifth wheel, pintle hook, or converter dolly) is the articulation point and the weakest link in stability.

Combination vehicles weigh more and stop slower than single units: total stopping distance grows with weight, and air brake systems add lag time between pedal and trailer brake application.

Offtracking and rearward amplification increase with the number of trailers; a triple-trailer rig can amplify a steering input at the rear trailer several times over the tractor's movement.

A tractor-trailer turns about a point between the drive axles and trailer axles; the shorter the wheelbase, the sharper the turn but the greater the offtracking at the trailer.

Sway is most dangerous when speed, load height, and sudden steering combine; a light trailer behind a heavy tractor is more prone to trailer swing than a loaded one.

The fifth wheel must be greased and locked; an unlocked or improperly latched fifth wheel allows the trailer to separate under load or braking.

Air lines (service and emergency/supply) must be connected and free of leaks; a disconnected emergency line sets the trailer spring brakes, which is the intended fail-safe.

Jackknifing occurs when drive wheels lock or lose traction and the trailer pushes the tractor; it is more likely on slick surfaces and with an empty or lightly loaded trailer.

The trailer is fed by two lines: the service line (blue, controlled by the foot valve) and the emergency/supply line (red, supplies reservoir pressure and signals a breakaway).

A breakaway: the emergency line separates, pressure drops, and the trailer spring brakes apply automatically - this is a required fail-safe, not a malfunction.

The tractor protection valve closes the tractor's air supply to the trailer if pressure falls too low, preserving tractor braking; it also seals the coupler when lines are disconnected.

The trailer hand valve (trolley valve) applies trailer brakes only; it is used for testing, never for normal stopping because it can cause a jackknife.

Spring brakes apply when air pressure is released; they cannot be released without sufficient air, so a trailer with drained tanks will not roll.

The relay valve on the trailer speeds brake application and release by sending reservoir air directly to the brake chambers.

The emergency line's gladhand is typically on the trailer's left side and the service line's on the right (or as marked); crossed lines cause brake malfunction and must be corrected.

Drain trailer air tanks daily; moisture and oil in the tanks can freeze or corrode valves and cause brake drag or failure.

Before coupling, check the fifth wheel: jaws open, locking mechanism released, mounting bolts tight, and the plate greased.

Back under the trailer slowly and squarely; after contact, tug-test by pulling gently forward with the trailer brakes set to confirm the jaws are locked.

Connect the emergency (red) line first, then the service (blue) line, to charge the trailer and release spring brakes; reverse the order when uncoupling.

Raise the landing gear to firm ground contact before pulling out; lower the trailer only until the gear touches the ground, not so far that the tractor lifts.

Lock the fifth wheel release handle with its safety latch; a missing or open latch allows the trailer to uncouple in motion.

When uncoupling, set the trailer brakes, lower the landing gear, disconnect lines and light cord, then pull the tractor slowly forward until clear of the kingpin.

Check the kingpin and fifth wheel jaws for wear or cracks; a worn kingpin can slip out of the jaws under load.

Never couple to a trailer whose kingpin or upper plate is damaged; the trailer may separate at highway speed.

Walk-around includes: coupling system, air lines and electrical cord, landing gear, trailer frame and body, doors, and lights.

Check the fifth wheel for proper engagement: no gap between the upper and lower plates, jaws closed around the kingpin, release handle latched.

Inspect air lines for cracks, chafing, and leaks; gladhand seals must be present and the lines must not drag on the ground.

Test the trailer brakes: with the tractor brakes released and the trailer brakes applied, the trailer should hold; a leak-down test confirms the system holds pressure.

Check tires for tread depth, sidewall damage, and proper inflation; dual tires must not touch and should be matched in size.

Verify all lights: clearance, marker, brake, turn, and license plate lamp, plus the reflective tape or reflectors.

Check the landing gear: fully raised, crank handle secured, and no missing parts.

Confirm the load is secured and the trailer doors latched; an unsecured load or open door is a violation and a hazard.

Turn wide: swing the tractor out before the turn so the trailer's rear wheels clear the inside curb; do not cut the corner.

Use the pivot point method: the trailer follows a path inside the tractor's path, so the rear wheels track closer to the inside of the turn.

Maintain a constant slow speed through the turn; braking mid-turn can cause the trailer to swing or the tractor to skid.

Check mirrors continuously during the turn; the trailer's rear and side must be visible to confirm clearance.

When changing lanes, signal early, check mirrors, and allow extra time; a long vehicle occupies more than one lane during the maneuver.

Do not turn from the wrong lane; a wide turn from the right lane when turning left can strike vehicles or curbs.

At intersections, watch for low clearance, overhead wires, and tight corners; a combination vehicle needs more room than a single unit.

Keep the trailer centered in the lane; drifting causes tire wear and can lead to a sideswipe or off-tracking into adjacent lanes.

Total stopping distance = perception distance + reaction distance + brake lag distance + braking distance; brake lag is longer with air brakes and trailers.

Brake firmly but smoothly; locking the drive wheels can cause a jackknife, and locking the trailer wheels can cause trailer swing.

Use the trailer hand valve only for testing; using it for normal braking can cause the trailer to swing out.

On slippery surfaces, reduce speed and increase following distance; the trailer's weight pushes the tractor and lengthens stopping distance.

If the trailer starts to swing, release the brakes and steer in the direction of the skid to regain control.

If the tractor drive wheels lock and the rig jackknifes, release the brakes and steer to correct; do not hold the brakes.

Engine braking and downshifting help control speed on downgrades; use a low gear before the descent, not after.

Anti-lock braking systems (ABS) on tractor and trailer help prevent wheel lock; keep steady pressure on the brake pedal during an ABS event.

Back slowly and use a spotter when possible; a combination vehicle has large blind spots behind and to the sides.

Steer the trailer by turning the wheel in the direction you want the trailer's rear to go; the tractor moves opposite the trailer's rear.

Use the mirrors and get out to check clearance if unsure; a spotter or ground guide reduces the risk of striking objects.

Backing a combination vehicle requires more space and time; plan the maneuver and avoid backing on a curve or in traffic when possible.

When parking, set the parking brakes, chock the wheels if on a slope, and lower the landing gear before uncoupling.

Park on level ground; if on a slope, turn the wheels toward the curb and use chocks to prevent rolling.

Do not back with the trailer brakes applied or the trailer hand valve set; the trailer will not track and the rig can jackknife.

Check overhead clearance and ground surface before backing; soft ground can cause the trailer to sink or the tractor to lose traction.

Offtracking is the difference between the path of the front wheels and the rear wheels; a longer wheelbase or more trailers increases it.

Rearward amplification is the increase in lateral acceleration from the tractor to the rear trailer; it grows with speed and the number of trailers.

A triple-trailer combination has the highest rearward amplification and is most prone to rollover in sudden maneuvers.

Sway (fishtailing) occurs when the trailer's rear swings side to side; it is worsened by speed, light loads, and abrupt steering.

A light trailer behind a heavy tractor is more likely to swing than a loaded trailer; load distribution matters.

Rollover risk increases with a high center of gravity, fast turns, and sudden lane changes; slow down before curves.

Crosswinds and passing trucks can push a light trailer sideways; reduce speed and grip the wheel firmly.

Offtracking can cause the trailer to strike curbs, signs, or vehicles at intersections; swing wide and check mirrors.

Cargo must be secured with tiedowns, straps, chains, or shoring; the number and strength depend on the load weight and type.

Aggregate working load limit of tiedowns must be at least 50% of the cargo weight for most loads; check the specific rules for your load.

Headache rack and front-end structure protect the cab from shifting cargo; ensure they are in place and undamaged.

Distribute weight evenly and keep the center of gravity low; an unbalanced load increases rollover and sway risk.

Check the load after the first few miles and periodically during the trip; straps can loosen as the load settles.

Cover loads that could blow off or spill; tarps must be secured and not flap.

Inspect the trailer floor and walls for damage that could let cargo shift or fall through.

Do not exceed axle or gross weight ratings; overloaded trailers brake poorly and are more prone to tire failure.

At railroad crossings, stop, look, and listen; a combination vehicle needs more time to clear the tracks, so do not start across until you are sure you can clear.

Never stop on the tracks; if the vehicle stalls, get everyone out and move away from the tracks, then call for help.

Use flashers and headlights at dusk and in poor visibility; a long vehicle is harder to see.

In an emergency, steer to a safe stop, set the parking brake, and place warning devices (reflectors or flares) behind the vehicle.

Place warning devices within 10 minutes of stopping: at 10, 100, and 200 feet behind the vehicle on a two-lane road, or as required by law.

If a tire blows, hold the wheel firmly, slow gradually, and pull off the road; do not brake hard.

If the trailer breaks away, the emergency line sets the trailer spring brakes; stay clear and call for help.

Report crashes and hazardous material spills immediately; do not move injured persons unless there is immediate danger.

The heavier the combination, the longer the stopping distance; a fully loaded tractor-trailer can take significantly farther to stop than a passenger car.

The tractor's rear axles carry the trailer's kingpin weight; overloading the drive axles reduces steering traction and increases tire wear.

A converter dolly has its own axle and couples a second trailer; its air lines and electrical connections must be checked like any trailer.

Pintle hook couplings are used for heavy trailers; the safety chains and air lines must be properly connected.

The trailer's spring brakes are the primary parking brake; they apply when air pressure is lost.

A combination vehicle's blind spots are larger than a single unit's; use mirrors and signal early.

Load height and weight distribution affect rollover; keep the center of gravity low and centered.

Regular inspection of coupling, brakes, and tires prevents most combination-vehicle failures.

The tractor protection valve closes when pressure drops below about 60 psi, preserving tractor air for braking.

The trailer spring brakes apply when the emergency line is disconnected or pressure is lost; this is a fail-safe design.

The service line controls trailer brake application; a leak in the service line reduces braking force.

The emergency line supplies air to the trailer reservoir and signals a breakaway; it must be connected first.

The relay valve on the trailer reduces lag time by applying reservoir air directly to the brake chambers.

Drain air tanks daily to remove moisture; frozen lines can cause brake failure in cold weather.

The trailer hand valve applies trailer brakes only; use it for testing, not normal braking.

Check gladhand seals and lines for leaks; a leaking line can cause the trailer brakes to drag or fail.

Before coupling, check the fifth wheel jaws are open and the release handle is out.

Back under the trailer slowly; after contact, tug-test with the trailer brakes set to confirm the jaws are locked.

Connect the emergency line first, then the service line; this charges the trailer and releases the spring brakes.

Raise the landing gear fully before pulling out; a partially raised gear can strike the ground.

Lock the fifth wheel release handle with its safety latch; an open latch allows separation.

When uncoupling, set the trailer brakes, lower the landing gear to the ground, disconnect lines, then pull the tractor forward.

Inspect the kingpin and jaws for wear; a worn kingpin can slip out.

Never couple to a damaged trailer; the trailer may separate at speed.

Check the fifth wheel for proper engagement: no gap, jaws closed, handle latched.

Inspect air lines for cracks, chafing, and leaks; gladhand seals must be present.

Test the trailer brakes: with the trailer brakes applied, the trailer should hold.

Check tires for tread depth, sidewall damage, and inflation; dual tires must not touch.

Verify all lights: clearance, marker, brake, turn, and license plate lamp.

Check the landing gear is fully raised and the crank handle secured.

Confirm the load is secured and doors latched.

Check the coupling system, frame, and body for cracks or damage.

Turn wide to keep the trailer's rear wheels from striking the curb or a vehicle.

The trailer follows a path inside the tractor's path; the rear wheels track closer to the inside of the turn.

Maintain a constant slow speed through the turn; braking mid-turn can cause a swing.

Check mirrors continuously during the turn to confirm clearance.

Signal early and allow extra time when changing lanes.

Do not turn from the wrong lane; a wide turn from the right lane when turning left can strike objects.

Watch for low clearance, overhead wires, and tight corners.

Keep the trailer centered in the lane to avoid sideswipes.

Total stopping distance includes perception, reaction, brake lag, and braking distance.

Brake firmly but smoothly; locking the drive wheels can cause a jackknife.

Use the trailer hand valve only for testing; using it for normal braking can cause trailer swing.

On slippery surfaces, reduce speed and increase following distance.

If the trailer starts to swing, release the brakes and steer in the direction of the skid.

If the drive wheels lock and the rig jackknifes, release the brakes and steer to correct.

Use a low gear before a downgrade; engine braking helps control speed.

Keep steady pressure on the brake pedal during an ABS event.

Back slowly and use a spotter when possible.

Steer the trailer by turning the wheel in the direction you want the trailer's rear to go.

Use mirrors and get out to check clearance if unsure.

Plan the maneuver and avoid backing on a curve or in traffic when possible.

When parking, set the parking brakes and chock the wheels on a slope.

Lower the landing gear before uncoupling.

Park on level ground; turn wheels toward the curb on a slope.

Do not back with the trailer brakes applied; the trailer will not track.

Offtracking is the difference between the path of the front wheels and the rear wheels.

Rearward amplification is the increase in lateral acceleration from the tractor to the rear trailer.

A triple-trailer combination has the highest rearward amplification.

Sway is worsened by speed, light loads, and abrupt steering.

A light trailer behind a heavy tractor is more likely to swing.

Rollover risk increases with a high center of gravity and fast turns.

Crosswinds can push a light trailer sideways.

Offtracking can cause the trailer to strike curbs or vehicles at intersections.

Cargo must be secured with tiedowns, straps, chains, or shoring.

Aggregate working load limit of tiedowns must be at least 50% of the cargo weight for most loads.

Headache rack and front-end structure protect the cab from shifting cargo.

Distribute weight evenly and keep the center of gravity low.

Check the load after the first few miles and periodically during the trip.

Cover loads that could blow off or spill.

Inspect the trailer floor and walls for damage.

Do not exceed axle or gross weight ratings.

At railroad crossings, stop, look, and listen; do not start across until you are sure you can clear.

Never stop on the tracks; if stalled, get everyone out and move away, then call for help.

Use flashers and headlights at dusk and in poor visibility.

In an emergency, steer to a safe stop, set the parking brake, and place warning devices.

Place warning devices within 10 minutes: at 10, 100, and 200 feet behind the vehicle on a two-lane road.

If a tire blows, hold the wheel firmly and slow gradually.

If the trailer breaks away, the emergency line sets the spring brakes; stay clear and call for help.

Report crashes and hazardous material spills immediately.