Arkansas CDL Combination Vehicles Test flashcards

32 cards. Read the term and the definition here. The deck at the top of this page is optional.

Brake lag distance

The distance a combination vehicle travels during the roughly 0.4-second delay before air pressure reaches the trailer brakes; it adds to total stopping distance.

Offtracking

The tendency of a combination vehicle's rear wheels to follow a path inside the front wheels during a turn, which can cause the trailer to strike curbs or pedestrians.

Swing-out

The outward swing of the rear of the tractor and the front of the trailer in the direction opposite the turn, requiring extra clearance on the outside of a turn.

Following distance rule

Allow one second per 10 feet of vehicle length at speeds under 40 mph, plus one extra second at speeds above 40 mph; a 60-foot rig at 55 mph needs 7 seconds.

Air pressure buildup test

With the engine at fast idle, pressure should rise from 85 to 100 psi within 45 seconds for a typical tractor-trailer; slower buildup indicates a compressor or leak problem.

Static air leak test

With the engine off and full pressure, leakage must not exceed 3 psi per minute for a single vehicle or 4 psi per minute for a combination vehicle.

Applied air leak test

Hold a full brake application for one minute with the engine off; leakage must not exceed 4 psi for a combination vehicle.

Low-air warning

A warning must activate by 60 psi, and the spring brakes must fully apply automatically between 20 and 45 psi as pressure falls.

Tractor protection valve

A valve that closes and cuts off air to the trailer when pressure drops into the 20-45 psi range, preserving tractor brakes and triggering a trailer emergency application.

Trailer hand valve

A control that applies only the trailer brakes; it must never be used for parking or normal stopping because it can cause a jackknife.

ABS purpose

Antilock braking prevents wheel lockup and maintains steering control during hard braking; it does not shorten stopping distance on all surfaces.

Trailer ABS lamp

An amber lamp that stays on after the bulb check indicates a trailer ABS fault; the trailer still has normal brakes but no antilock function.

Tractor ABS lamp

A lamp that stays on after the bulb check indicates a tractor ABS fault; the system reverts to standard braking without antilock protection.

ABS braking technique

During an ABS event, hold firm steady pressure on the brake pedal and steer; do not pump the brakes, which defeats the system.

Tug test

After backing under a trailer, pull forward twice with the trailer brakes set to confirm the fifth wheel jaws have locked around the kingpin.

Coupling visual check

A tug test alone is not proof of coupling; visually confirm the closed jaws and safety latch, and check that the tractor frame clears the trailer apron.

Uncoupling sequence

Park on level ground, set the tractor brake, chock the trailer wheels, lower the landing gear, disconnect lines and light cord, release the fifth wheel, then pull forward slowly.

Glad hand color coding

Emergency line is red and service line is blue; connect the red line first when charging and disconnect the blue line first when uncoupling.

Fifth wheel inspection

Check the fifth wheel, kingpin, locking jaws, and safety latch during pre-trip; an unlatched release handle can allow the trailer to separate.

Landing gear inspection

Check the trailer landing gear for cracks, bent legs, and missing feet or crank handle; gear must be fully raised before moving.

Tire tread minimums

Front steer tires need at least 4/32 inch of tread depth; all other tires need at least 2/32 inch; duals must match and be properly inflated.

Trailer apron height check

The trailer apron must not be so low that the tractor frame or cab strikes it in a turn, nor so high that the kingpin cannot seat in the fifth wheel.

Right turn technique

Start from as far right as practical and swing wide to the left to keep the trailer off the curb, but do not swing into oncoming traffic.

Left turn technique

Allow extra room on left turns because the trailer offtracks to the right; do not cut the corner.

Backing a combination

Steer the bottom of the steering wheel toward the direction you want the trailer to go; if the trailer is not straight, pull forward to straighten it.

Curve driving rule

Reduce speed before entering a curve and use steady throttle through it; hard braking in a curve can cause a rollover or skid.

Drive-wheel skid

A jackknife occurs when the tractor's rear wheels lock and the trailer pushes the tractor sideways; release the brakes and steer in the direction of the skid.

Trailer skid

A trailer skid occurs when the trailer wheels lock and the trailer swings out; release the brakes and steer in the direction the trailer is sliding.

Front-wheel skid

A front-wheel skid occurs when the steering axle locks; release the brakes and steer in the direction you want to go, then straighten when traction returns.

Trailer breakaway

If a trailer separates, the emergency line parts and the trailer spring brakes apply automatically; do not try to stop the trailer by hand.

Cargo securement forces

The securement system must withstand 0.8 g forward, 0.5 g rearward, and 0.5 g lateral force of the cargo weight.

Bridge formula

A federal limit on the weight carried on any group of axles based on the distance between them; shorter axle spacing allows less weight.