Who has to take the CDL general knowledge test?

The manual says the general knowledge test is taken by all applicants. Whatever class or endorsements you want, this test is required. Check your state for its exact rules.

How many questions are on the general knowledge test?

Your state sets the number of questions and the passing score. Check your state's CDL manual. See our guide on how many questions are on the CDL test for more.

What sections of the manual should I study for it?

Section 2, Driving Safely, is the core. Section 3 says you must understand basic cargo safety rules to get a CDL, so read it too. Section 2 also has basic hazmat rules, but the hazmat endorsement test uses Section 9.

CDL General Knowledge Test: Topics and Numbers to Know

The CDL general knowledge test is the knowledge test every CDL applicant takes. The manual says it is "taken by all applicants," so you cannot skip it, and it is where most of your permit prep time should go.

Who needs the general knowledge test?

Everyone who wants a CDL. That is true for any class of license, and it is true whether or not you want any endorsements. The other knowledge tests, like air brakes or hazmat, depend on the truck and the load. This one does not.

Some of the other tests are added on top of it. See which CDL tests you need for how they stack up.

Your state sets the number of questions and the passing score. Check your state's CDL manual, and read how many questions are on the CDL test for what to expect.

What the test covers

Section 2 of the manual, Driving Safely, is the main source. It says this section has "knowledge and safe driving information that all commercial drivers should know." The manual lists these topics:

Vehicle inspection
Basic control of your vehicle
Shifting gears
Seeing
Communicating
Space management
Controlling your speed
Seeing hazards
Distracted driving
Aggressive drivers and road rage
Night driving and driver fatigue
Driving in fog
Winter driving
Hot weather driving
Railroad-highway crossings
Mountain driving
Driving emergencies
Antilock braking systems
Skid control and recovery
Accident procedures
Fires
Alcohol, other drugs, and driving
Hazardous materials rules

Section 3, Transporting Cargo Safely, says you "must understand basic cargo safety rules to get a CDL." Plan to study it with Section 2.

Section 2 does not have air brake, combination vehicle, doubles or passenger information. Those have their own sections and tests. If you need a hazmat endorsement, study Section 9 as well.

The numbers drivers miss

All of these come straight from the manual. The stopping, following, warning device and railroad numbers are in Section 2. The cargo numbers are in Section 3. The alcohol rule is in Section 1, under CDL disqualifications.

Topic	The number or rule
Following distance, below 40 mph	At least 1 second for each 10 feet of vehicle length
Following distance, at greater speeds	Add 1 second
40-foot vehicle	4 seconds, or 5 seconds over 40 mph
60-foot rig	6 seconds, or 7 seconds over 40 mph
How far ahead to look	Most good drivers look at least 12 to 15 seconds ahead
Total stopping distance at 55 mph	A minimum of 419 feet, in ideal conditions
Perception distance at 55 mph	142 feet (1¾ seconds)
Reaction distance at 55 mph	61 feet
Braking distance at 55 mph	About 216 feet
Double the speed, 20 to 40 mph	Impact and braking distance are 4 times greater
Triple the speed, 20 to 60 mph	9 times greater
Wet road	Reduce speed by about one-third
Packed snow	Reduce speed by a half or more
Hydroplaning	Can start at speeds as low as 30 mph if there is a lot of water
Parked on a two-lane or undivided road	Warning devices within 10 feet of the front or rear corners, and 100 feet behind and ahead
Hill or curve blocks the view	Place a device back beyond it so drivers can see the vehicle within 500 feet. Move the rear-most triangle back down the road
Emergency warning devices	3 red reflective triangles, 6 fusees or 3 liquid burning flares
Required stop at a crossing with no stop line	No closer than 15 feet, no farther than 50 feet from the nearest rail of the nearest track
Time to clear a crossing, tractor-trailer	At least 14 seconds for one track, more than 15 for two
Cargo tie-downs	At least one for each 10 feet of cargo, and never fewer than two
First cargo check	Within the first 50 miles
Later cargo checks	After 3 hours or 150 miles, and after every break
Alcohol and a CMV	Illegal at a BAC of .04% or more

Mirrors, signals and hazard lights

Check your mirrors before any trip. The manual says mirror adjustment "can only be checked accurately when the trailer(s) are straight." Adjust each mirror to show some part of your vehicle, so you have a reference point.

Convex mirrors show a wider area. But everything looks smaller and farther away than it really is.

Signal early and signal continuously. Use your four-way flashers when you stop at the side of the road, and when you stop at a railroad crossing where a stop is required.

Railroad crossing rules

A full stop is required when the nature of the cargo makes a stop mandatory under state or federal rules, or when the law otherwise requires it. When you stop, check for traffic behind you, stop gradually, and turn on your four-way flashers.

Never race a train. Do not shift gears while crossing the tracks. Do not stop on the tracks. If you get stuck, get out and away from the tracks, then call 911 or the emergency number posted at the crossing.

Test yourself

Try 10 exam-style questions built from the official CDL manual.

Traps on the test

Adding the extra second. The 1 second per 10 feet rule changes at speeds over 40 mph. Add 1 second. A 40-foot rig needs 4 seconds below 40 mph and 5 above.
Stopping distance has three parts. Perception, reaction and braking. Total stopping distance is all three added together.
Speed and braking distance. Double the speed and braking distance is 4 times longer, not 2 times.
Empty trucks. They do not brake better. The manual says empty trucks need greater stopping distances because an empty vehicle has less traction.
Hydroplaning. Do not use the brakes. Release the accelerator and push in the clutch.
Tie-down counts. A 20-foot load needs at least 2. A tiny load still needs at least 2.
Warning devices. Hold the triangles between you and oncoming traffic as you walk them out, so drivers can see you.
Passive versus active crossings. Passive has no traffic control device. Active has flashing red lights, with or without bells, or lights with bells and gates.

How to study it in a week

Day one, read Section 2 up to Seeing Hazards. Day two, memorize the following distance, stopping distance and speed numbers from the table. Day three, read the rest of Section 2, from distracted driving through mountain driving. Day four, read driving emergencies, ABS, skids, accident procedures, fires and alcohol. Also read the alcohol rule in Section 1.3.

Day five, read Section 3 on cargo. Day six, write the table from memory and fix what you miss. Day seven, take a full practice test, then read why each wrong answer is wrong.

Short on time? Start with the General Knowledge practice test. Missed questions show you which section to reread first.