Georgia CDL Combination Vehicles Test flashcards
Georgia CDL Combination Vehicles Test · Build recall with a focused review session.
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- Combination vehicle
- A tractor or truck coupled to one or more trailers, such as a tractor-semitrailer, doubles, or triples. The coupling point is the articulation point and the weakest link in stability.
- Fifth wheel
- The horseshoe-shaped coupling plate on the tractor that locks around the trailer kingpin. It must be greased and its jaws fully closed and latched before the vehicle moves.
- Jackknife
- A loss-of-control condition in which the tractor and trailer fold toward each other, usually after drive wheels lock or lose traction. It is more likely on slick roads and with light trailers.
- Trailer sway
- Side-to-side fishtailing of the trailer, worsened by speed, light loads, and abrupt steering. Releasing the brakes and steering in the direction of the skid helps regain control.
- Service line
- The blue air line controlled by the foot valve that applies the trailer brakes. A leak or disconnection reduces trailer braking force.
- Emergency line
- The red air line that supplies reservoir pressure to the trailer and signals a breakaway. If it separates, trailer spring brakes apply automatically as a fail-safe.
- Tractor protection valve
- A valve that closes the tractor's air supply to the trailer when pressure falls too low, preserving tractor air for braking. It also seals the coupler when lines are disconnected.
- Trailer hand valve
- A trolley valve that applies trailer brakes only. It is used for testing, never for normal stopping, because it can cause a jackknife or trailer swing.
- Spring brakes
- Brakes applied by spring force when air pressure is released. They are the fail-safe parking and emergency brake and cannot be released without sufficient air.
- Relay valve
- A trailer valve that sends reservoir air directly to the brake chambers, speeding brake application and release and reducing lag time.
- Tug test
- After coupling, pulling gently forward with the trailer brakes set to confirm the fifth wheel jaws are locked around the kingpin before driving away.
- Landing gear
- The trailer's support legs. Lower them to firm ground contact before uncoupling, and raise them fully before pulling out so they do not strike the ground.
- Kingpin
- The pin under the trailer's upper plate that locks into the fifth wheel jaws. A worn or damaged kingpin can slip out and allow the trailer to separate.
- Coupling order
- Connect the emergency (red) line first, then the service (blue) line, to charge the trailer and release spring brakes. Reverse the order when uncoupling.
- Pre-trip walk-around
- An inspection of the coupling system, air lines, electrical cord, landing gear, frame, body, doors, lights, tires, and load before driving. It catches defects that cause breakdowns or crashes.
- Leak-down test
- A check that the air brake system holds pressure with the brakes applied. A rapid pressure drop indicates a leak that must be repaired before driving.
- Gladhand seal
- The rubber gasket inside the air line coupler. A missing or damaged seal causes leaks that reduce trailer braking or set the spring brakes.
- Turn wide
- Swinging the tractor out before a turn so the trailer's rear wheels clear the inside curb. Cutting the corner causes the trailer to strike curbs, signs, or vehicles.
- Pivot point
- The point between the drive axles and trailer axles about which a tractor-trailer turns. The trailer's rear wheels track inside the tractor's path.
- Lane control
- Keeping the trailer centered in its lane and signaling early before lane changes. A long vehicle occupies more than one lane during maneuvers.
- Brake lag
- The delay between pressing the brake pedal and the trailer brakes applying, caused by air traveling through the lines. It lengthens total stopping distance.
- Total stopping distance
- The sum of perception distance, reaction distance, brake lag distance, and braking distance. It grows with weight and with the number of trailers.
- Skid recovery
- Releasing the brakes and steering in the direction of the skid to regain control. Holding the brakes can worsen a jackknife or trailer swing.
- ABS event
- When anti-lock braking activates, keep steady pressure on the brake pedal. Do not pump the brakes; the system modulates pressure automatically.
- Backing a trailer
- Turning the wheel in the direction you want the trailer's rear to go. The tractor moves opposite the trailer's rear, so the maneuver needs space and slow speed.
- Spotter
- A person outside the vehicle who guides the driver during backing. A spotter reduces blind-spot crashes and helps confirm clearance.
- Offtracking
- The difference between the path of the front wheels and the rear wheels. It increases with wheelbase and the number of trailers and can cause the trailer to strike curbs.
- Rearward amplification
- The increase in lateral acceleration from the tractor to the rear trailer. It grows with speed and trailer count and raises rollover risk, especially for triples.
- Tiedown working load limit
- The rated strength of straps, chains, or shoring. For most loads, the aggregate working load limit must be at least 50 percent of the cargo weight.
- Load distribution
- Spreading cargo evenly and keeping the center of gravity low. Poor distribution increases sway, rollover risk, and axle overloading.
- Railroad crossing procedure
- Stop, look, and listen, and do not start across until sure the vehicle can clear the tracks. Never stop on the tracks; if stalled, evacuate and call for help.
- Warning devices
- Reflectors or flares placed behind a stopped vehicle within 10 minutes: at 10, 100, and 200 feet on a two-lane road, or as required by law.