Alabama CDL General Knowledge: Driving Safely: Space, Speed, and Survival

Safe driving is mostly about managing space and speed before a problem develops. Know the three parts of total stopping distance: perception distance (how far you travel while recognizing the hazard), reaction distance (travel while your foot moves to the brake), and braking distance (travel from brake application to stop). Perception and reaction together are the "thinking distance" and grow directly with speed; braking distance grows with the square of speed, so doubling speed roughly quadruples braking distance.

Following and being followed

Use the one-second-per-ten-feet rule for following distance: at speeds under 40 mph stay at least one second behind for every 10 feet of vehicle length, and add one second above 40 mph. A 60-foot combination at 55 mph needs about 7 seconds. Add more space in rain, fog, snow, darkness, or when following a vehicle that blocks your view. If someone tailgates, increase your own following distance so you can slow gradually rather than brake hard.

Traps in questions

• Speed and stopping distance: questions often imply stopping distance doubles with speed. It does not; only thinking distance doubles.
• Downshifting before a downgrade: choose the gear before you start down, not after speed builds.
• Tire failure or blowout: hold the wheel firmly, stay off the brake, and let the vehicle slow gradually.
• Hydroplaning: ease off the accelerator; do not brake hard or steer sharply.

Rule of thumb: if you cannot stop within the distance you can see to be clear, you are driving too fast for conditions - regardless of the posted limit.

Transporting Cargo Safely: Weight, Securement, and Balance

Cargo rules exist to protect you, the load, and everyone around you. Start with three numbers: Gross Vehicle Weight Rating (GVWR) is the maximum loaded weight of a single vehicle; Gross Combination Weight Rating (GCWR) applies to a tractor-trailer; and axle weight ratings cap what each axle can carry. Overloading any of these is a violation even if the total looks fine. Alabama and federal limits also cap axle and gross weights, so know that legal limits and manufacturer ratings both apply - you must satisfy the lower one.

Securing the load

Cargo must be tied down so it cannot shift, fall, or leak. General cargo needs at least one tie-down for every 10 feet of article length, with a minimum of two tie-downs for articles longer than 5 feet but 10 feet or less. The working load limit of the tiedown assemblies must be at least half the weight of the cargo. Headboards, blocking, and dunnage keep loads from sliding forward; covers protect against spillage.

Balance and inspection

Keep the center of gravity low and centered. A high or off-center load raises rollover risk and can overload one axle. After loading and before driving, check that the load is balanced, secured, and within ratings; re-check tiedowns within the first 50 miles and every 150 miles or 3 hours afterward.

Traps

• Confusing GVWR with the weight of the cargo alone.
• Forgetting that a load can be legal in total but over on one axle.
• Assuming covers replace tiedowns - they do not.

Rule of thumb: if you would not want it behind you at highway speed, it is not secured well enough.

Air Brakes: The System and the Checks

Air brakes use compressed air instead of hydraulic fluid, and the system has three braking functions you must be able to name: the service brake (normal foot pedal braking), the parking brake (spring brakes applied when air pressure drops or the knob is pulled), and the emergency brake (the spring brakes acting automatically on a pressure loss).

How pressure behaves

A compressor builds pressure and stores it in tanks. A governor cuts the compressor out around 120-135 psi and back in around 100 psi. A safety valve protects the tanks from overpressure. When pressure falls too low (roughly 60 psi or below in most systems), the low air pressure warning must activate - a buzzer and/or light. Below about 20-45 psi, the spring brakes fully apply. This is why you must never drive with a pressure loss: you will lose your brakes.

The tests

• Leak test (static): with a fully charged system and engine off, release the parking brake and watch the gauges. Pressure should not drop more than about 3 psi in one minute for a single vehicle, or 4 psi for a combination.
• Applied leak test: hold the brake pedal down and watch for excessive drop (about 3 psi per minute single, 4 psi combination).
• Low pressure warning test: pump the pedal to reduce pressure and confirm the warning comes on before 60 psi.
• Spring brake test: continue pumping; the parking brake knob should pop out (spring brakes apply) in the 20-45 psi range.

Traps

• Confusing the governor cut-out with the safety valve.
• Thinking the parking brake is hydraulic - it is spring-applied, air-released.
• Forgetting that a rapid pressure drop while braking means you must stop and fix the problem, not "pump" your way through it.

Rule of thumb: build full pressure, engine off, and listen for leaks - if you can hear air escaping, do not move the vehicle.

Combination Vehicles: Coupling, Pivot Points, and Stability

A combination vehicle bends, and that changes everything. The pivot point - the fifth wheel on a tractor-trailer - means the trailer follows a different path than the tractor. In a turn, the trailer off-tracks, cutting the corner, so you must swing wider and watch the trailer's rear wheels in the mirrors. The longer the wheelbase and trailer, the more off-tracking.

Coupling and uncoupling

Inspect before coupling: fifth wheel open and greased, kingpin and apron sound, air lines and electrical cord ready. Back under slowly, hear and feel the fifth wheel jaws lock around the kingpin, then pull-test by tugging forward gently with the trailer brakes set - the tractor should not move. Connect air lines (emergency/red line first is a common convention; supply/blue second), then electrical cord, then raise landing gear and check lights. Uncoupling reverses the order: lower landing gear, disconnect lines, pull the release handle, and pull out slowly.

Stability and braking

Combinations are more prone to rollover and jackknife. Rollover risk rises with speed in turns and high center of gravity. A trailer jackknife happens when the trailer's wheels lock and swing out; a tractor jackknife happens when the drive wheels lock. Anti-lock brakes (ABS) help prevent wheel lock, but they do not shorten stopping distance on all surfaces - they preserve steering control. Rearward amplification means the last trailer in a multi-trailer set swings wider than the first.

Traps

• Skipping the pull-test after coupling.
• Forgetting that the red (emergency) line supplies the trailer's emergency braking.
• Believing ABS lets you drive faster - it does not.

Rule of thumb: if you did not hear the jaws lock and feel the pull-test hold, you are not coupled.

Vehicle Inspection: The Pre-Trip Routine

The pre-trip inspection is a systematic walk-around that proves the vehicle is safe before you move it. Examiners look for a method, not memorized phrases: start at one point and work around the vehicle so nothing is skipped. A common approach is front, left side, rear, right side, then in-cab, then brake tests.

What to check and why

• Engine compartment: fluid levels (oil, coolant, power steering, washer), belts and hoses for cracks or fraying, and leaks under the vehicle.
• Lights and reflectors: headlights (high and low), turn signals, four-way flashers, brake lights, clearance and marker lights, and reflectors - all clean and working.
• Tires and wheels: tread depth (at least 4/32 inch on front steer tires, 2/32 inch elsewhere), sidewalls free of cuts and bulges, lug nuts tight with no rust trails, and no missing spacers.
• Brakes and suspension: brake chambers and hoses secure, slack adjusters not obviously out of adjustment, springs and air bags intact.
• Coupling (if combination): fifth wheel, kingpin, safety latches, air lines.
• In-cab: seat and seatbelt, mirrors adjusted, gauges, horn, wipers, defroster, parking brake, and the warning indicators.

The brake checks

With the engine running, build full pressure, then shut it off. Check for leaks, confirm the low-pressure warning, and confirm the spring brakes apply as pressure drops. Then test the service brake by moving slowly and stopping.

Traps

• Describing what a part does instead of pointing to it and saying it is secure and undamaged.
• Forgetting to check the last item on the walk-around because you rushed.
• Skipping the in-cab checks after the exterior walk-around.

Rule of thumb: point, name, and state condition - "this tire, tread depth adequate, sidewall intact, lug nuts tight."

Basic Control: Starting, Steering, and Stopping Smoothly

Basic control is about doing ordinary things - starting, backing, turning, stopping - without losing the vehicle. Before you move, complete the pre-trip inspection, adjust the seat and mirrors, fasten the seatbelt, and confirm the parking brake is set and the transmission is in neutral (or park).

Starting and stopping

Start the engine and let air pressure build. Release the parking brake only when you are ready to move. To stop, brake early and progressively; a heavy vehicle needs distance, and passengers or cargo can shift if you brake abruptly. Use the stab braking technique on vehicles without ABS when you need maximum braking: brake hard, release when wheels lock, brake again - do not pump gently.

Backing and turning

Backing is the highest-risk low-speed maneuver. Get out and look (GOAL) if unsure, use a spotter when available, and back slowly with the windows down or mirrors set to see the rear. When turning, remember that the rear wheels track inside the front wheels - swing wide enough to keep the trailer's rear tires off the curb, but not so wide that you cross into oncoming lanes. Right turns are the tightest and most likely to clip a curb or a pedestrian.

Distractions and speed

Keep both hands on the wheel, avoid reaching for objects, and never text. Speed limits are maximums for ideal conditions; reduce speed in rain, fog, construction zones, and at night.

Traps

• Releasing the parking brake before the engine has built air pressure.
• Turning too sharply and clipping the curb with the trailer's rear wheels.
• Assuming a spotter is optional - if you cannot see, you cannot back safely.

Rule of thumb: when in doubt while backing, stop, set the brake, and get out to look.

Shifting Gears: Matching Engine Speed to Road Speed

A manual transmission heavy vehicle has a narrow power band, so shifting is a skill you must demonstrate deliberately. The goal is to keep the engine in its efficient range and to never let the vehicle roll backward or lurch. Know the difference between upshifting (as speed rises) and downshifting (as speed falls or before a grade).

The sequence

To upshift: accelerate to the right rpm, press the clutch, move the shift lever through neutral to the next gear, release the clutch smoothly, and accelerate again. To downshift: slow to the correct speed for the lower gear, press the clutch, shift through neutral, and release the clutch. Do not skip gears on a downgrade - select the gear you will need before you start down, because you cannot safely shift while descending a steep grade with a heavy load.

Double clutching and floating

Some older non-synchronized transmissions require double clutching: clutch in, shift to neutral, clutch out, clutch in, shift to gear, clutch out. Modern synchronized transmissions often allow floating (shifting without the clutch) by matching engine speed, but this is a skill to learn, not a shortcut for exams. Questions test whether you understand why you match rpm - to avoid gear clash and to keep control.

Traps

• Thinking you can downshift to slow down instead of using the brakes - brakes are for slowing, gears are for matching speed.
• Shifting into a lower gear at too high a speed, which can over-rev the engine.
• Coasting in neutral, which reduces control.

Rule of thumb: slow down before you downshift, and pick your gear before the hill, not on it.

Seeing Hazards: Scanning for Trouble Before It Arrives

Seeing hazards is about anticipating problems early enough to act smoothly. The core skill is scanning - looking far ahead, checking mirrors regularly, and keeping your eyes moving rather than staring at the vehicle in front. Look at least 12-15 seconds ahead in urban areas and farther on open highway.

Types of hazards

• Road hazards: potholes, soft shoulders, narrow bridges, construction zones, and curves with limited sight distance.
• Traffic hazards: vehicles entering from side roads, tailgaters, and drivers who drift in their lane.
• Environment hazards: rain, fog, ice, glare, and darkness that reduce visibility and traction.
• Human hazards: pedestrians, cyclists, and distracted drivers.

Reading the situation

Watch for clues: brake lights ahead, a driver's head turning, a ball rolling into the road, or a vehicle weaving. These are clues that a hazard is developing. When you spot one, decide early whether to slow, change lanes, or increase following distance. The earlier you identify a hazard, the more options you have and the gentler your response can be.

Communicating

Use your lights, horn, and signals to make yourself visible. At night, dim high beams for oncoming traffic. In fog, use low beams - high beams reflect back and reduce visibility.

Traps

• Fixating on the vehicle directly ahead instead of scanning far down the road.
• Assuming a driver who is signaling will actually turn.
• Using high beams in fog or heavy rain.

Rule of thumb: look 12-15 seconds ahead, check mirrors every 5-8 seconds, and always have an escape route in mind.

Distracted Driving: Keeping Your Mind on the Road

Distraction is any activity that takes your eyes off the road, your hands off the wheel, or your mind off driving. A commercial driver faces all three at once, and a heavy vehicle needs far more distance to stop than a car - so a two-second glance at a phone can mean hundreds of feet traveled blind.

Types of distraction

• Visual: looking at a phone, GPS, or paperwork.
• Manual: eating, adjusting the radio, reaching for an object.
• Cognitive: arguing, daydreaming, or worrying about a schedule.
• Auditory: loud music or a phone conversation that pulls attention away.

Texting combines visual, manual, and cognitive distraction - the worst combination. Even hands-free calls are cognitively distracting.

What the rules require

Commercial drivers are held to strict standards. Follow your company policy and the law: no texting while driving, and phone use only when permitted and safe. Pull over to a safe place to use a phone, check a map, or handle paperwork. Set your GPS and mirrors before you move. Keep your cab tidy so nothing rolls under the pedals.

Managing fatigue and emotion

Fatigue is a form of distraction. Take required rest breaks, and do not drive when drowsy. Anger or stress also pulls your mind off the road - calm down before you drive.

Traps

• Believing a hands-free device makes a call safe - it still distracts.
• Thinking a quick glance is harmless - at highway speed it covers a long distance.
• Ignoring company policy because the law seems less strict.

Rule of thumb: if it takes your eyes off the road, your hands off the wheel, or your mind off driving, do it after you stop.

Railroad-Highway Crossings: Stop, Look, and Listen

A train cannot stop quickly or steer around you, so crossings demand a deliberate, active approach. The core rule: slow down, look both ways, and listen - and never rely on the absence of a signal to mean the track is clear.

Approaching the crossing

As you approach, reduce speed and be ready to stop. Turn off distracting noise, open the window, and listen. Look both ways and check again before crossing. If a train is coming, stop well back from the tracks - at least 15 feet from the nearest rail - and wait. Never stop on the tracks; if traffic ahead is backed up, wait until you can clear the crossing completely before starting across.

Signals and devices

• Gates and flashing lights mean stop and wait until the gates are fully raised and lights stop flashing.
• Crossbucks (the X-shaped sign) mean the same as a yield - slow, look, listen, and be prepared to stop.
• Stop signs at a crossing require a complete stop.
• Pavement markings (an X and RR) warn of the crossing ahead.

Traps

• Driving around a lowered gate - never do this.
• Assuming a train is moving slowly because it looks far away; trains can appear closer and faster than they seem.
• Stopping too close to the tracks, where a passing train can strike the vehicle.

If you get stuck

If your vehicle stalls on the tracks, get everyone out and away from the tracks immediately, then call for help. Do not try to restart the vehicle while people remain inside.

Rule of thumb: stop at least 15 feet back, look both ways twice, and never start across unless you can clear the far side.