General Knowledge
What this domain covers
The General Knowledge domain tests the core rules you apply before and while driving any commercial motor vehicle (CMV): pre-trip inspection duties, basic control, shifting, backing, speed and space management, hazard perception, emergency handling, railroad crossings, and cargo securement. Ohio’s CDL General Knowledge test draws on federal CMV standards and state traffic law, so expect questions on vehicle classes, alcohol rules, and safe operating limits.
Core rules to know
- Vehicle classes: Class A is a combination with a GCWR of 26,001 lb or more and a towed unit over 10,000 lb. Class B is a single vehicle of 26,001 lb or more, or a combination towing 10,000 lb or less. Class C covers vehicles of 26,001 lb or less built for 16 or more passengers or used for placarded hazmat.
- Alcohol: Ohio applies the federal CDL threshold: 0.04% BAC. Refusing a required chemical test in a CMV carries at least a one-year CDL disqualification for a first offense.
- Following distance: Below 40 mph, allow one second per 10 feet of vehicle length. Above 40 mph, add one extra second.
- Railroad crossings: When a stop is required, stop 15 to 50 feet from the nearest rail, never shift gears while crossing, and cross only when you can clear the tracks completely.
- Cargo: Secure loads against shifting and falling; check tiedowns before departure and again during the trip.
Worked example
A 60-foot combination travels at 55 mph. One second per 10 feet gives 6 seconds. Because the speed is above 40 mph, add 1 second, for a minimum 7-second following gap. At 30 mph, the same vehicle needs 6 seconds. The extra second at highway speed buys perception and reaction distance, not just braking distance.
Traps that cost marks
- Treating the posted limit as a safe speed for a loaded CMV; it is only the maximum for ideal conditions.
- Misusing the railroad stop zone: stop no closer than 15 feet and no farther than 50 feet from the nearest rail.
- Pumping or fanning air brakes; use steady pressure and controlled stops unless the manufacturer’s procedure says otherwise.
- Confusing total stopping distance with braking distance; total includes perception, reaction, and braking distance.