Illinois CDL Combination cheat sheet

A combination vehicle stops more slowly than a single unit: total stopping distance equals perception distance plus reaction distance plus brake lag plus braking distance, and brake lag on a tractor-trailer is longer because air pressure must travel through the lines.

A fully loaded tractor-trailer needs about 20-40 percent more stopping distance than a passenger car at highway speed, and an empty combination can need even more because stiff suspension and light trailer weight reduce tire-to-road friction.

Rearward amplification: the last trailer in a multi-trailer combination swings wider than the tractor during a lane change, so a quick double lane change at highway speed can turn a smooth maneuver into a rollover.

Offtracking increases with wheelbase and with the number of towed units; a 53-foot trailer cuts corners so the rear wheels track several feet inside the path of the front wheels during a turn.

Drive through a curve at a speed that lets you hold your lane without leaning, then accelerate gently only after the tractor is straight; braking in a curve on a combination is the leading cause of trailer swing and rollover.

Check mirrors every 5-8 seconds and before every lane change; a tractor-trailer has large blind spots directly behind the trailer and along both sides that mirror adjustment must cover as fully as possible.

The heavier the load, the lower the safe speed on downgrades: use the same gear going down that you used going up, and brake only briefly and firmly rather than riding the brakes.

Keep at least one second of following distance per 10 feet of vehicle length at speeds under 40 mph, and add one extra second above 40 mph; a 60-foot combination therefore needs 7 seconds at 50 mph.

Static leak test: with the engine off, fully charged, and the brakes released, the air pressure should not drop more than 3 psi in one minute for a single vehicle or more than 4 psi for a combination; a greater drop means a leak.

Applied leak test: with the engine off and the brakes fully applied, the pressure should not drop more than 4 psi in one minute (single) or more than 6 psi (combination).

Low-air warning must activate before pressure falls below 60 psi; the spring brakes must automatically apply when pressure drops to roughly 20-45 psi, so the tractor-trailer stops on its own.

Tractor protection valve test: charge the trailer, shut the engine off, and step on the brake pedal; the valve should pop out at about 20-45 psi, protecting tractor air if a trailer line breaks.

After the pop-out test, restart and recharge to at least 100 psi, then push in the trailer air supply valve to confirm the trailer charges and the tractor protection valve resets.

Slack adjuster check: pull each brake chamber pushrod by hand; movement of about 1 inch or less is normal, and 2 inches or more means the brakes are dangerously out of adjustment and the vehicle must be placed out of service.

The combination has three air lines: service (blue) and emergency/supply (red) glad hands plus the electrical cord; the emergency line supplies air to the trailer and triggers trailer brakes if it separates.

Drain air tanks daily; moisture and oil in the system reduce braking performance, and the supply tank should be drained first, then the primary and secondary tanks.

Inspect the fifth wheel and apron before coupling: the jaws must be open, the locking mechanism free, the mounting bolts tight, and the fifth wheel greased and tilted down toward the rear of the tractor.

Back slowly and straight so the kingpin enters the throat of the fifth wheel; after the tractor stops, pull forward gently twice to confirm the jaws have locked and the kingpin is seated.

Always use a tug test before raising the landing gear: pull forward in a low gear with the trailer brakes set; if the trailer does not move, the coupling is secure.

After locking, verify the release handle is in the locked position and insert the safety latch or cotter pin; a fifth wheel that is not fully locked can drop the trailer in motion.

Connect the air lines after coupling: the emergency (red) line goes to the emergency glad hand and the service (blue) to the service glad hand, then open the shut-off valves and check for leaks.

Raise the landing gear fully before driving; a partially lowered landing gear can strike pavement, railroad tracks, or a loading dock and damage the trailer or cause a crash.

Uncoupling order: park on level ground, set the parking brakes, lower the landing gear to firm contact with the ground, disconnect the air and electrical lines, release the fifth wheel jaws, then pull forward slowly.

Chock the trailer wheels before uncoupling on any slope, and never leave a trailer standing on its landing gear without the tractor attached unless the wheels are chocked.

Pre-trip inspection of a combination covers three areas: the tractor (engine compartment, cab, lights, brakes), the coupling system (fifth wheel, kingpin, air lines, electrical cord), and the trailer (frame, suspension, brakes, lights, doors, and tires).

Check the fifth wheel for cracks, bends, missing or loose bolts, and worn jaws; inspect the kingpin for bends, cracks, and wear, and confirm the apron is not damaged.

Inspect all tires for tread depth, cuts, bulges, and proper inflation; dual tires must not touch, and any tire with fabric showing or a tread separation must be replaced before driving.

Test all lights with a helper or by walking around: headlights, turn signals, four-way flashers, brake lights, clearance lights, and trailer marker lights must all work before departure.

Check the air lines for cracks, cuts, and wear, and ensure the glad hands have good seals; the electrical cord should not be pinched, worn, or dragging.

Verify the landing gear is fully raised, the crank handle is secured, and the trailer support frame is not cracked or bent.

Check that the trailer doors are closed and latched, the cargo is secured, and the trailer is not overloaded on any axle; axle weight limits vary by state and by bridge formula.

During a walk-around, look under the trailer for debris, hanging air lines, or dragging parts, and confirm the mud flaps and splash guards are intact.

A combination vehicle's center of gravity is higher than a passenger car's, so the rollover threshold is lower; a loaded tractor-trailer can overturn at lateral acceleration well below what a car can handle.

Rollover usually happens in three ways: driving too fast into a curve or ramp, a quick lane change that sets the trailer swinging, and running off the shoulder and overcorrecting back onto the pavement.

The cargo's center of gravity matters: a high, top-heavy load raises rollover risk, and an unsecured or shifting load can move the center of gravity and cause a loss of control.

The trailer's rear wheels follow a shorter path than the tractor's front wheels, so the trailer can strike a curb, sign, or pedestrian on the inside of a turn even when the tractor clears it.

A tractor-trailer's pivot point is the fifth wheel; the trailer pivots around it, so steering inputs at the tractor are amplified at the trailer's rear.

Load distribution matters: too much weight on the rear trailer axles can overload tires and reduce steering traction on the tractor, while too much on the drive axles can lighten the steer axle and cause loss of steering.

Roll stability is reduced by a high center of gravity, soft or underinflated tires, and a partially filled tanker with shifting liquid; slow down before the curve, not in it.

The posted ramp speed for a passenger car is not a safe speed for a loaded combination; use a lower gear and enter curves well below the posted limit.

Offtracking is the difference between the path of the front wheels and the path of the rear wheels; it increases with wheelbase and with the number of trailers, so a long combination needs a wider swing.

Right turns: swing wide to the left before turning, but do not swing into an adjacent lane; check the right mirror throughout the turn to keep the trailer's rear wheels clear of the curb.

Left turns: approach from the right side of your lane if space allows, and remember the trailer cuts the corner, so watch for vehicles, poles, and pedestrians on the inside of the turn.

Before a lane change, signal, check mirrors, and turn your head to check the blind spot; a combination has a large blind spot on both sides and directly behind, so a quick glance is not enough.

Complete the lane change smoothly and at a steady speed; abrupt steering sets the trailer swinging, and the rear of the trailer can swing into the lane you just left.

When turning, do not start the turn until the tractor's front wheels are at the point where the turn begins; starting too early cuts the corner and the trailer's rear wheels will strike the curb.

On multilane roads, keep the combination in the right lane except to pass, and allow extra room when merging or being passed because of the vehicle's length and slower acceleration.

Use turn signals early and hold them through the turn; a combination's length means other drivers need more warning before you change direction.

Back only when necessary and always with a helper outside the vehicle; if no helper is available, get out and check behind the trailer before backing, then back slowly with frequent stops.

Use the mirrors and the helper's hand signals; agree on signals before backing, and stop immediately if you lose sight of the helper.

Back toward the driver's side (left) whenever possible; backing to the right is harder because the trailer disappears from the right mirror sooner.

Use the tractor's steering to push the trailer: turning the wheel right while backing swings the trailer's rear left, and turning left swings it right; make small corrections early.

Pull-up (GOAL) whenever the trailer drifts off line: stop, pull forward to straighten, then resume backing rather than trying to correct with large steering inputs.

Park on level ground when possible; if you must park on a slope, set the parking brakes, place the transmission in the lowest gear or park, and chock the wheels.

When parking, leave enough space for the trailer's rear swing and for other vehicles to pass; do not block fire lanes, loading zones, or railroad crossings.

Before backing, check for overhead obstructions, low wires, and pedestrians, and turn on four-way flashers to warn other drivers.

A drive-wheel skid happens when the tractor's drive wheels lose traction; release the accelerator and steer in the direction you want to go, and do not apply the brakes until the wheels regain traction.

A trailer skid (trailer swing) happens when the trailer's wheels lock or lose traction; release the brakes and steer the tractor in the direction the trailer is sliding to straighten the combination.

A jackknife is a severe fold between tractor and trailer, usually caused by locking the drive wheels or by braking hard on a slippery surface; release the brakes and steer to recover.

Use the brakes gently and progressively on slippery surfaces; hard braking locks wheels, and locked wheels on a combination lead to jackknifing or trailer swing.

If a tire blows out, hold the steering wheel firmly, keep the vehicle straight, and slow down gradually; do not brake hard or steer sharply, which can cause a rollover or loss of control.

If the brakes fail, downshift to a lower gear, use the emergency/parking brake gradually, and look for an escape ramp or a safe runoff area; do not pump the brakes.

When a skid begins, take your foot off the accelerator and avoid hard braking; steer smoothly to correct the slide, and look and steer where you want the vehicle to go.

Anti-lock braking systems (ABS) prevent wheel lockup; keep firm, steady pressure on the brake pedal during an emergency stop and do not pump the brakes.

Approach every railroad crossing at a speed that lets you stop before the tracks; look and listen for trains, and never rely on the crossing signals alone.

Never stop on the tracks: a long combination may not clear the crossing before the light changes, so wait until there is room on the far side before starting across.

At a crossing with a steep approach, the trailer's rear can drag or the landing gear can strike the tracks; cross at an angle if possible and check clearance before proceeding.

If your vehicle stalls or gets stuck on the tracks, get everyone out immediately and move away from the tracks, then call the railroad emergency number posted at the crossing.

Before crossing, check that the trailer's rear wheels will clear the tracks and that the landing gear is fully raised; a dragging landing gear can catch on the rails.

Watch for hazards ahead: stopped traffic, construction, and merging vehicles can force a combination to stop on a crossing; slow down and keep enough space ahead.

At night or in bad weather, use four-way flashers when crossing and increase following distance; a long vehicle needs more time to clear the crossing.

Never try to beat a train: a train cannot stop quickly, and a combination that stalls on the tracks is a fatal hazard; stop, look, and listen before every crossing.