Free, full Idaho CDL general knowledge test practice right here in your browser — real exam format (50 questions, 80% to pass), diagnostic and adaptive modes, spaced-repetition review, and a readiness dashboard. No signup, no paywall — your progress is saved automatically on this device.
What is 'brake lag' and why is it important?
D. The delay between pressing the brake pedal and the brakes actually applying, typically about one-half second for air brakes — Brake lag is the approximately half-second delay caused by air traveling through the system before the brakes engage. Combined with reaction time, CMV stopping distances are significantly longer than cars.
When pulling double trailers, which trailer should be placed directly behind the tractor?
C. The heavier trailer — The heavier trailer should always be placed directly behind the tractor. A heavy rear trailer creates a 'crack-the-whip' effect and increases jackknife risk.
What does a four-digit number on a placard or orange panel identify?
B. The UN/NA identification number for the hazardous material — The four-digit UN/NA identification number on a placard or orange panel identifies the specific hazardous material being transported.
A sign that one of your tires has failed is:
D. A loud bang, vibration, or the vehicle thumping or pulling to one side — A bang, sudden vibration, or pulling to one side often signals a blowout, so be ready to hold the wheel and slow down safely.
Before backing this tractor-trailer into the dock, the safest first step is to:
D. Get out and walk around to check behind and around the vehicle — Always do a walk-around (Get Out And Look) before backing, since mirrors leave blind spots and conditions can change.
What is 'fatigue' as a safety concern for CDL drivers, and what is the only safe remedy?
B. Fatigue impairs reaction time, judgment, and alertness as much as alcohol; the only remedy is actual sleep — not caffeine or brief naps under 10 minutes — Research shows that severe fatigue impairs driving as much as a BAC of 0.08%. The only effective remedy is adequate sleep. Stimulants mask fatigue temporarily but do not restore cognitive function.
The proper way to use the brakes on a long, steep downgrade is to:
B. Select a low gear and use light, intermittent (snub) braking to keep a safe speed — Choosing a low gear lets engine braking do most of the work while brief snub braking holds your speed without overheating the brakes.
CDL safety scenario 57: During an en-route inspection, what should you check after the first 50 miles?
D. Cargo securement, tires, brakes, lights, and coupling devices — Cargo securement, tires, brakes, lights, and coupling devices. Commercial drivers are expected to manage this situation before it becomes a crash risk. The CDL manual emphasizes controlling the vehicle, inspecting safety-critical systems, and correcting hazards promptly.
When must placards be removed from a vehicle?
B. When the vehicle no longer contains the hazardous material that required the placard — Placards must be removed when the hazardous material that required the placard is no longer aboard — maintaining incorrect placards can mislead emergency responders.
Under FMCSA Hours of Service rules, a property-carrying driver may drive a maximum of how many hours after 10 consecutive off-duty hours?
A. 11 hours — Property-carrying drivers may drive a maximum of 11 hours after taking 10 or more consecutive off-duty hours. This is the 11-Hour Driving Limit under FMCSA regulations.
The Idaho CDL general knowledge test has 50 questions, and you need 80% to pass — at least 40 correct answers. The practice tests on this page use the same format. The 80% passing score is a federal FMCSA standard used by every state.
80%. You can miss at most 10 of the 50 questions. The readiness dashboard on this page tracks whether you're consistently scoring above that bar.
Yes. Every practice test on this page and everything in the DMVPrep iPhone app is free — no ads, no paywall, no account.
Federal motor carrier safety regulations (FMCSA) — the same rules every state's CDL exam is drawn from. Every question in the DMVPrep app cites the regulation or handbook section it comes from.
Yes — the DMVPrep app includes all 3,745+ questions in Spanish, and the whole app works in Spanish.