About the Alabama CDL Knowledge Test
The test is taken in person at an Alabama ALEA Driver License office. It is multiple choice, untimed, and covers material from the Alabama Commercial Driver's License Manual — the same document this guide is based on. There is no online testing option.
If you fail, you can retake the test. There is no mandatory waiting period between attempts, though each attempt costs $5. Most people who study thoroughly pass on their first try.
✓ How This Guide Works
Each section below covers one part of the CDL manual. Expand it to see the key concepts and numbers you need to memorize. The sections marked High Priority have the most questions on the real exam — study those first.
CDL Manual — Section by Section
Overview of CDL classes, endorsements, and restrictions. Foundational knowledge — few direct test questions, but important context.
- Class A: combinations over 26,001 lbs GCWR with towed unit over 10,000 lbs
- Class B: single vehicle over 26,001 lbs GVWR
- Class C: 16+ passengers or HazMat requiring placards
- Endorsements: H (HazMat), N (Tanker), T (Doubles/Triples), P (Passenger), S (School Bus)
- You can only hold one CDL from one state at a time
The largest section and the most heavily tested. Covers space management, visibility, communication, speed, and emergency handling.
- Following distance: 1 second per 10 feet of vehicle length at speeds under 40 mph; add 1 second for speeds over 40 mph
- Stopping distance: At 55 mph — perception (61 ft) + reaction (61 ft) + braking (170 ft) = approximately 292 feet
- Low beam headlights: See 250 feet ahead. Never outrun your headlights.
- High beam headlights: See 500 feet ahead
- Check mirrors every 5–8 seconds while driving
- Blind spots (no-zones) exist directly behind, directly in front, and on both sides of a truck
- Right turns: swing wide to the right, not left — cutting the corner causes rollovers
- In a skid: take your foot off the brake or accelerator, steer in the direction you want to go
- Emergency stops on highways: signal, check mirrors, brake gradually, pull off completely
- Work zone speed limits apply even when workers are not present
Covers weight limits, cargo securement, and load balance. Commonly tested — know the numbers cold.
- Maximum gross weight: 80,000 lbs (federal limit on interstate highways)
- Max single axle: 20,000 lbs; Max tandem axle: 34,000 lbs
- Cargo must be inspected within the first 50 miles, then every 3 hours or 150 miles
- Cargo should be distributed so 60% of weight is on the front axles
- Blocking and bracing must prevent cargo from shifting forward, backward, or sideways
- Tiedowns: at least 1 per 10 feet of cargo, never fewer than 2
- Oversize loads require permits, escort vehicles, and may have restricted travel hours
- Dry bulk cargo (grain, sand) is prone to shifting — drives like a liquid load when loose
Pre-trip inspection is tested on both the knowledge test and the skills test. Know the 7-step process and what you're checking at each step.
- 7 steps: (1) Approach, (2) Engine compartment, (3) Inside cab, (4) Start engine/check gauges, (5) Lights, (6) Walkaround, (7) Check signal lights
- Brakes: check slack adjusters, brake drums, hoses, and brake lining thickness
- Tires: minimum 4/32" tread depth on front axles; 2/32" on other axles
- Steering wheel: no more than 10° of play (2" on a 20" wheel)
- During walkaround: check all lights, mirrors, reflectors, mudflaps, and landing gear
- On combination vehicles: also check coupling devices, air/electrical lines, kingpin, and fifth wheel
- Enroute: check cargo, tires, brakes, and coupling devices at each stop
Covers upshifting and downshifting techniques for both manual and automatic transmissions.
- Double clutching required on most manual transmissions — release clutch, shift to neutral, re-engage, shift to next gear
- Timing shifts by engine RPM, not by feel or sound
- Downshift before descending a grade — never rely solely on brakes on a long descent
- Stab braking: apply brakes fully, release before wheels lock, repeat — for vehicles without ABS
- ABS does NOT shorten stopping distance — it only prevents wheel lockup to maintain steering control
- Jake brakes (engine brakes) provide additional braking on downgrades — must be off in wet conditions on some routes
Critical for Class A applicants. Covers coupling/uncoupling, rearward amplification, and trailer handling.
- Rearward amplification: the rear of a double or triple trailer swings further than the cab on a turn — the more trailers, the more amplification
- Trailer brakes: never use hand valve to park (spring brakes should hold) — hand valve is for testing only
- Fifth wheel: must be fully locked with no gap between kingpin and fifth wheel jaws
- Coupling sequence: inspect fifth wheel → back slowly → connect air lines → check/test connection → raise landing gear
- Uncoupling: park on level ground → chock wheels → lower landing gear → disconnect lines → release kingpin
- Converter dollies: used to convert semi-trailers into full trailers for doubles/triples
- If trailer brakes fail: trailer may jackknife or push the tractor out of lane
Required only if you're pursuing the T (Doubles/Triples) endorsement — separate knowledge test.
- The rear trailer of a double has the most rearward amplification — most dangerous in a turn or emergency
- Inspect converter dolly before coupling — must have correct hitch rating
- Longest combination: triple 28-foot trailers = 105 feet total
- Some states restrict doubles/triples on certain highways — check route permits
- Always place the heaviest trailer directly behind the tractor
Required for the N (Tank) endorsement. Covers liquid surge, loading, and emergency procedures.
- Liquid surge: liquid in a partially filled tank moves with momentum — braking causes forward surge, turning causes side surge
- Never drive a tanker more than 80% full — liquid needs room to expand
- High center of gravity makes tankers prone to rollover — slow down significantly before turns
- Baffled tanks have bulkheads with holes — reduce surge but don't eliminate it
- Unbaffled tanks (milk tankers, food tanks) have maximum surge — require very smooth driving
- Check tank outlets, valves, and dome covers before every trip
Required for H endorsement. TSA background check required separately. Extensive rules — these are the most commonly missed questions.
- 9 HazMat classes: Explosives, Gases, Flammable Liquids, Flammable Solids, Oxidizers, Poisons, Radioactive, Corrosives, Miscellaneous
- Shipping papers: must list proper shipping name, hazard class, ID number, and packing group
- Shipping papers location: within reach while driving; on the seat or in the door pouch
- Placards required when carrying 1,001 lbs or more of a placardable material
- Some materials require placards in ANY amount (Class A/B explosives, poison gas, radioactive, etc.)
- No HazMat through tunnels or near crowds without checking route restrictions
- Park 300 feet from crowds or fires; 5 feet from road edge
One of the most tested sections. If you have air brakes on your test vehicle, you must know these numbers perfectly.
- Normal operating air pressure: 100–125 psi
- Low pressure warning: activates at 60 psi
- Spring brakes activate: between 20–45 psi (automatic parking brake)
- Air leakage test: with engine off and brakes released, pressure should not drop more than 3 psi per minute for single vehicles; 4 psi for combinations
- Applied leakage test: with brakes applied, should not drop more than 4 psi per minute (single) or 6 psi (combination)
- Governor cuts in at 100 psi and cuts out at 125 psi
- S-cam brakes most common; wedge brakes and disc brakes also used
- Never pump air brakes — you'll deplete the reservoir
- Brake fade: caused by overheating from excessive use on downgrades — test brakes before long descents
Specific to vehicles with air brakes — tested on both knowledge and skills exam.
- Build pressure to governor cutout (around 125 psi) before moving
- Low air warning test: fan down brakes to 60 psi — warning light/buzzer should activate
- Spring brake test: fan down further to 20–45 psi — spring brakes should activate automatically
- Static pressure test: key off, note pressure, wait 1 minute — should not drop more than 2 psi
- Check air lines for leaks: listen for hissing, check connections at all couplings
- Drain air tanks daily to remove water — water freezes in cold weather and causes brake failure
Zero-tolerance rules — multiple questions on this topic guaranteed.
- BAC limit in a CMV: 0.04% (half the regular 0.08% limit)
- Illegal to drive within 4 hours of consuming alcohol
- Refusal to take a BAC test = automatic disqualification
- Out-of-service for 24 hours if found with BAC of 0.02–0.039%
- Hours of Service: 11 hours max driving after 10 consecutive off-duty hours
- 14-hour window: cannot drive after 14 hours on-duty from start of shift
- 30-minute break required after 8 hours of driving
- 60/70-hour rule: cannot drive after 60 hours on-duty in 7 days (or 70 hours in 8 days)
- Log books or ELD (Electronic Logging Device) required on most interstate trips
Top 10 Numbers to Memorize
These specific values appear on the knowledge test repeatedly. Know every one of them.
| Rule | Number |
|---|---|
| CDL knowledge test passing score | 80% (40/50) |
| BAC limit for CDL holders in a CMV | 0.04% |
| Normal air brake operating pressure | 100–125 psi |
| Low air pressure warning activation | 60 psi |
| Spring brakes activate below | 20–45 psi |
| Maximum daily driving hours (HOS) | 11 hours |
| On-duty window before mandatory reset | 14 hours |
| Required break after 8 hours driving | 30 minutes |
| Max federal gross vehicle weight | 80,000 lbs |
| Cargo inspection interval (after first 50 mi) | Every 3 hrs / 150 mi |
Study Strategy — Pass on Your First Try
📖 The 3-Pass Method
Pass 1: Read the full Alabama CDL manual once without stopping — just for familiarity. Pass 2: Go section by section using this guide and write down the key numbers. Pass 3: Take practice tests until you're scoring 90%+ consistently. Only then book your appointment at ALEA.
Most people who fail the knowledge test made the same mistake: they skimmed the manual instead of studying it. The test is specifically designed to catch people who read quickly without absorbing the specific numbers — brake pressures, stopping distances, cargo inspection intervals, BAC limits.
📝 Focus Your Study Time
Sections 2 (Driving Safely), 4 (Pre-Trip Inspection), 10 (Air Brakes), and 12 (Alcohol/HOS) account for the majority of test questions. If your study time is limited, go deep on those four sections first, then fill in the rest.