Arizona CDL Combination Vehicles cheat sheet

Inspection order: left side, front, right side, rear, then coupling area and engine compartment; announce each hazard you find aloud during the CDL skills test.

Tug test: after coupling, pull forward gently in low gear with the trailer hand valve or tractor protection valve applied; the tractor must not move if the fifth wheel jaw has locked.

Fifth wheel checks: jaws fully closed around the kingpin, release handle in the locked position, safety latch engaged, and no gap between apron and fifth wheel.

Before uncoupling, chock the trailer wheels, lower the landing gear to firm ground, and disconnect air lines and electrical cord before pulling the release handle.

Air line routing: connect the emergency (supply) line first and disconnect it last so the trailer spring brakes stay released and the tractor protection valve stays closed.

Slack adjuster check: with brakes released, pull the slack adjuster by hand; more than about 1 inch of movement at the clevis indicates adjustment is needed.

Trailer height before coupling: apron of the trailer should be just below the fifth wheel so the tractor lifts it slightly as the kingpin enters the jaws.

Doors, mirrors, lights, tires, and mud flaps are inspected last; any defect noted in the walk-around must be corrected or reported before driving.

Off-tracking: the rear wheels of a combination follow a shorter path than the front wheels; the longer the wheelbase, the greater the off-track, so swing wide on turns.

Right turns: approach in the left portion of the lane, move to the right just before the turn, and watch the trailer's rear wheels in the mirror to avoid curb strikes.

Stopping distance grows with weight and speed; a loaded combination needs roughly 20-40 percent more distance than a bobtail at the same speed, so increase following distance.

Following distance rule: at least one second per 10 feet of vehicle length below 40 mph, plus one extra second above 40 mph - about 7 seconds for a 60-foot rig.

Braking on downgrades: select a gear that holds the speed without brakes, use engine braking, and apply brakes in short firm applications rather than riding them.

Speed on curves: reduce speed before entering the curve; a combination rolls over at lower speeds than a single vehicle because of its high center of gravity.

Lane changes: signal early, check both mirrors for the trailer's full length, and do not change lanes until the trailer clears the previous lane completely.

Backing a combination: back toward the driver's side, use a helper or get out and check, and steer the trailer by turning the wheel toward the direction you want the trailer to go.

Compressor builds air to the governor cut-out pressure (typically 120-125 psi); cut-in is usually around 100 psi, and the low-air warning must activate by 60 psi.

Static leak test: with engine off and full pressure, release the service brake and hold; loss should not exceed 3 psi per minute for a single vehicle or 4 psi for a combination.

Applied leak test: fully apply the brake pedal and hold; leakage should not exceed 4 psi per minute on a combination vehicle.

Tractor protection valve closes automatically when pressure drops to about 20-45 psi, sealing the tractor's air supply and applying the trailer's spring brakes.

Spring brakes apply automatically when air pressure falls below about 20-45 psi; never drive a vehicle whose spring brakes will not release at normal pressure.

Trailer hand valve (spike) is for testing trailer brakes only; it is not a parking brake and must not be used to hold the vehicle on a grade.

Brake adjustment: with the brake released, push the slack adjuster; more than about 1 inch of free stroke at the clevis means the brakes need adjustment.

Drain air tanks daily to remove moisture and oil; in cold weather, moisture freezes and can block valves, causing brake failure or dragging brakes.

Jackknife types: drive-wheel (tractor) jackknife occurs when the drive wheels lock and the tractor swings; trailer jackknife occurs when the trailer wheels lock and the trailer swings out.

Anti-lock braking systems prevent wheel lock-up; with ABS, hold firm steady pressure on the brake pedal and do not pump the brakes.

If the drive wheels begin to skid, release the brake pedal to regain rolling traction, then reapply; steering into the skid while braking can worsen a jackknife.

Recovery from a rear-wheel skid: release the brakes, look and steer where you want to go, and avoid hard braking until the wheels roll again.

Emergency stop on a highway: brake firmly, keep the wheel straight, pull as far onto the shoulder as possible, and set parking brakes and warning devices.

Front-wheel skid: the vehicle will not steer; release the brake to let the wheels roll, then steer gently in the intended direction of travel.

Downshift before a steep downgrade; if brakes fail, use engine braking, look for an escape ramp, and use the emergency brake gradually rather than locking the wheels.

Hydroplaning: reduce speed, avoid sudden braking or steering, and hold the wheel steady until tires regain contact with the road.

Federal axle weight limits: 20,000 lb on a single axle, 34,000 lb on a tandem axle group, and 80,000 lb gross vehicle weight without a permit.

Bridge formula limits the weight on any group of axles based on the number of axles and the distance between the first and last axle.

Cargo securement: one tiedown for every 10 feet of cargo length, with a minimum of two tiedowns, and aggregate working load of tiedowns at least half the cargo weight.

Tiedowns must be attached to the vehicle's anchor points, not to the cargo itself, and must be tight enough that the cargo cannot shift.

Weight distribution: place heavy cargo over or near the drive axles, keep the center of gravity low, and avoid overloading the steer axle, which reduces steering control.

A load that shifts forward can overload the steer axle and lighten the drive axles, reducing traction; check the load after the first few miles.

Height limit for commercial vehicles is generally 13 feet 6 inches to 14 feet; check the route and posted clearances before driving.

Front of the cargo must be blocked or braced to prevent forward movement during braking; rear must be braced against rearward movement.

Railroad crossings: stop within 50 feet but not less than 15 feet from the nearest rail when carrying passengers or hazardous materials, or when the crossing requires a stop.

At a railroad crossing, turn off the radio, open the window, look and listen in both directions, and do not shift gears while crossing the tracks.

Never stop on the tracks; if the vehicle stalls, get everyone out and away from the tracks, then call the railroad using the posted emergency number.

Hazardous materials: a placarded load requires the driver to stop at railroad crossings, and the driver must carry the proper shipping papers within reach.

Skid recovery in rain or snow: reduce speed by at least one-third on wet roads and by half on snow-packed roads; use gentle steering and braking inputs.

Ice and snow: use chains where required, check chain tightness after a short distance, and increase following distance to at least double the normal gap.

Fog and heavy rain: use low-beam headlights, reduce speed, and increase following distance; never use high beams in fog because they reflect back.

Emergency warning devices: place reflective triangles within 10 minutes of a stop; 10 feet behind and 100 feet ahead of the vehicle on a two-lane road, and 10 feet behind and 100 feet ahead and behind on a divided highway.