CDL general knowledge test: what is on it and how to study
The topics Section 2 covers, the numbers that come up again and again, and a study order that gets most drivers to 90% in about ten days.
The general knowledge test is the one every CDL applicant takes, and the one that decides whether you leave the office with a permit. It has 50 questions, you need 40 right, and almost every question comes from Section 2 of the CDL manual, with a handful from Section 1 on the permit rules. Section 2 is about 50 pages. Here is what is in it and how to work through it.
What Section 2 covers
| Part | Topic | What the questions ask |
|---|---|---|
| 2.1 | Vehicle inspection | The seven-step pre-trip, what to look for on tyres, brakes, lights, coupling, and the limits that take a vehicle off the road |
| 2.2 to 2.3 | Basic control and shifting | Backing with a helper, upshifting and downshifting by engine speed and road speed, retarders |
| 2.4 to 2.5 | Seeing and communicating | Mirror checks, scanning 12 to 15 seconds ahead, signalling, when to use the horn and flashers |
| 2.6 to 2.7 | Space and speed | Following distance, the rules for turning, stopping distance, speed on curves and downgrades, hydroplaning |
| 2.8 to 2.9 | Hazards and distraction | Spotting hazards early, aggressive drivers, mobile phones |
| 2.10 to 2.13 | Night, fog, winter, hot weather | Reduced visibility, tyre chains, bleeding tar, checking tyres in heat |
| 2.14 to 2.16 | Railroad crossings, mountains, emergencies | Stopping at crossings, brake fade, escape ramps, steering out of a skid, what to do when brakes fail |
| 2.17 to 2.20 | Skids, accidents, fires | Drive-wheel skids, protecting the scene, the right extinguisher for each fire |
| 2.21 to 2.23 | Alcohol, drugs, fatigue | The 0.04 limit, the out-of-service rule, warning signs of fatigue |
| 2.24 | Hazardous materials rules | What every driver must know even without the endorsement: placards, when a load needs them |
The numbers that keep coming back
A short list carries a large share of the test. Learn these exactly.
- Following distance: one second for every 10 feet of vehicle length below 40 mph, plus one second above 40 mph. A 60-foot rig at 55 mph needs 7 seconds.
- Looking ahead: 12 to 15 seconds, which is about a quarter of a mile at highway speed.
- Alcohol: 0.04% blood alcohol is the limit for driving a commercial vehicle. Any detectable alcohol puts you out of service for 24 hours.
- Tyre tread: 4/32 of an inch on the steer tyres, 2/32 on all others.
- Stopping: total stopping distance is perception plus reaction plus braking distance; doubling speed roughly quadruples braking distance.
- Hydroplaning: can start at speeds as low as 30 mph with little tread or standing water.
- Railroad crossings: buses and placarded hazmat vehicles stop 15 to 50 feet from the nearest rail; do not shift gears while crossing.
- Mirrors and signals: signal before turning, at least 100 feet before a turn in town; turn the signal off after the turn.
- Fires: a B:C extinguisher for electrical and fuel fires; never use water on an electrical or petrol fire.
- Fatigue and hours: the danger hours are midnight to 6 a.m. and mid afternoon; the hours-of-service rules are in Section 1 and your state's supplement.
A ten-day study order
- Days 1 to 2: inspection. The pre-trip is the largest single topic and it reappears on the skills test. Learn the seven steps and the tyre, brake and coupling limits.
- Days 3 to 4: space, speed and seeing. This is where the following-distance and stopping-distance questions live.
- Day 5: hazards, night, weather. Fast to read, easy points.
- Day 6: emergencies, skids, fires, crossings. Procedures, not numbers; read them in order.
- Day 7: alcohol, drugs, fatigue, hazmat basics, Section 1 permit rules.
- Days 8 to 10: mock exams. Full 50-question sets. After each one, read the manual paragraph behind every miss, not just the explanation.
Expect your first mock exam to land in the 70s. Most drivers who follow the order are at 90% by the third.
The general knowledge practice test has ten free questions from the PassRig bank with the manual section on each. The app has the rest, in full-length mock exams.