The manual treats night driving as three problems — the driver, the roadway and the vehicle — and the knowledge test pulls from all three. Then it adds the hours of service limits, which trip more people up because they are arithmetic rather than judgment.
Drive within your headlights
The rule that generates the most night-driving questions is this: adjust your speed so your stopping distance stays inside your sight distance. If you cannot stop within the stretch of road your headlights light up, you are driving blind and you will find the hazard by hitting it.
The manual gives you the numbers to work with:
- Low beams show you roughly 250 feet of road ahead.
- High beams show you roughly 350 to 500 feet.
- Dirty headlights can cut that output by as much as half.
So on low beams your speed has to let you stop in about 250 feet — total stopping distance, meaning perception, reaction and braking together, not braking alone. That is why the manual says to use high beams whenever you legally can. Running low beams all night out of habit or courtesy is a mistake it names directly: it throws away most of your warning.
Glare, dirty glass and the night pre-trip
Glare is the other driver factor. Oncoming high beams blind you for several seconds, and the manual makes the cost concrete: at 55 mph you cover more than half a football field while your eyes recover. The fix is not to stare it down — look toward the right edge of the road and steer by it until the vehicle passes.
Dimming is the other half of that. The CDL manual tells you to dim your high beams within 500 feet of an oncoming vehicle, and within 500 feet when following one. The enforceable distance is set by state law, though: 500 feet for oncoming traffic is common, but a number of states set the following distance at 200 or 300 feet. Study your own state's figures.
Before a night run the manual wants:
- You rested and alert — not starting a trip already tired.
- Clean glasses if you wear them, and no sunglasses after dark.
- A clean windshield and clean mirrors, because road film turns oncoming headlights into a wall of glare.
- Every lamp and reflector checked. 49 CFR 393.9 requires them to be capable of operating at all times, and prohibits them being obscured by the load, its covering or dirt.
The 11-hour, 14-hour and 30-minute rules
These are federal and exact. For property-carrying drivers, 49 CFR 395.3 sets four limits:
- 10 consecutive hours off duty before you may drive at all.
- 11 hours of driving maximum in the window that follows.
- 14 consecutive hours — you may not drive after the 14th hour from coming on duty. Off-duty time taken inside that window does not push the 14 back.
- A 30-minute interruption — you may not drive after 8 cumulative hours of driving time without a consecutive 30-minute break. Since the 2020 rule that interruption can be off duty, sleeper berth, or on duty not driving, so a half-hour fuel-and-inspection stop counts.
The distinction that catches people out: the 11 counts driving time only, while the 14 counts everything from the moment you come on duty. Loading, waiting at a dock, a long lunch — all of it burns the 14 and none of it burns the 11.
The 60-hour and 70-hour limits
On top of the daily clocks, 395.3 caps the rolling week:
- 60 hours on duty in any 7 consecutive days, if your carrier does not operate every day of the week.
- 70 hours on duty in any 8 consecutive days, if it does.
Which one applies is decided by the carrier's schedule, not by you. Both count on-duty time, which 395.2 defines as all time from when you begin work, or are required to be ready to work, until you are relieved of it — much broader than driving.
You may reset the 7- or 8-day period with 34 or more consecutive hours off duty. The restart is optional; you can also simply let the oldest day roll off the back of the period.
The exceptions that trip people up
- Sleeper berth split. Property-carrying drivers may split the 10 hours into two qualifying periods: one of at least 7 consecutive hours in the sleeper berth, and another of at least 2 consecutive hours off duty, in the sleeper berth, or both. Together they must total at least 10. When they pair correctly, neither period counts against the 14-hour window — the familiar 8/2 and 7/3 splits.
- Adverse driving conditions. You may drive up to 2 additional hours, and since 2020 the on-duty window stretches by the same 2 hours, giving 13 hours of driving inside 16. But 395.2 defines the conditions narrowly: snow, ice, sleet, fog, other adverse weather, or unusual road or traffic conditions that were not known and could not reasonably have been known when you started. Rush hour you sit in every day does not qualify.
- Short-haul. A driver who stays within a 150 air-mile radius of the normal work reporting location, returns there, and is released within 14 consecutive hours is excused from the logging requirement and from the 30-minute break. The 11-hour driving limit and the 14-hour window still apply.
- Passenger-carrying drivers run different numbers. Under 395.5 it is 10 hours of driving after 8 consecutive hours off duty, with no driving after 15 hours on duty. The 60/70 limits are the same. If you are testing for a passenger or school bus endorsement, learn both sets.
Fatigue is a rule, not a feeling
Hours of service is the outer boundary. Inside it, 49 CFR 392.3 makes fatigue itself a violation: no driver may operate a commercial vehicle while their ability or alertness is so impaired, or so likely to become impaired, through fatigue or illness that it is unsafe to begin or continue. A clean log is not a defense for being unfit to drive.
The manual is blunt about the remedy. Sleep cannot be saved up in advance or borrowed against, and it recommends 7 to 8 hours in every 24. It notes that many heavy-vehicle crashes happen between midnight and 6 a.m., and that most people are least alert after midnight. Do not count on coffee, the radio or an open window — when your body needs sleep, only sleep works. If you feel sleepy, stop driving.
Where to practice these questions
Hours-of-service questions are short scenarios where one wrong figure changes the answer. CDL Prep Exam 2026: Permit runs them inside General Knowledge with an explanation after each answer, and reviews the ones you missed so the limits stop blurring together.
Before test day, do two things. Read the night driving and staying-alert sections of your own state's CDL manual — the figures above come from the AAMVA model manual every state adapts, but your state's book is what the test is written from. Then drill hours of service questions until you can rebuild 11, 14, 30 and 60/70 from memory.