Ohio CDL General Knowledge key terms

The maximum total weight a single vehicle is designed to carry, including the vehicle itself, fuel, passengers, and cargo, as specified by the manufacturer.

The maximum allowable combined weight of a towing vehicle plus its trailer and all cargo, set by the manufacturer of the power unit.

The portion of a vehicle's total weight carried by one axle or axle group; Ohio and federal limits apply per axle as well as overall.

How cargo weight is spread across axles and the ground; poor distribution can overload an axle, lighten steering tires, or reduce braking traction.

A horseshoe-shaped coupling plate mounted on the tractor that locks onto the trailer kingpin, allowing the trailer to pivot while towing.

The vertical steel pin under a trailer's front that locks into the tractor's fifth wheel, forming the main towing connection.

Retractable legs under a trailer's front that support it when uncoupled; they must be fully raised and secured before towing.

A braking system powered by compressed air, in which loss of pressure causes brakes to apply on most heavy vehicles, providing a fail-safe design.

Loss of braking power caused by overheating from repeated or prolonged use, common on long downgrades; downshifting and controlled braking help prevent it.

The linkage that connects a brake chamber pushrod to the brake shoe; excessive pushrod travel means brakes are out of adjustment and unsafe.

A device that uses engine compression to slow the vehicle on grades; it does not replace service brakes but reduces their heat buildup.

Selecting a lower gear before a downgrade so the engine helps control speed and service brakes are used less, reducing overheating risk.

A systematic check of the vehicle's critical parts before driving, including brakes, tires, lights, coupling devices, and fluid levels, to catch defects early.

Side-to-side movement of a trailer, often caused by improper weight distribution, excessive speed, or steering corrections; easing off the accelerator helps regain control.

The tendency of a trailer's rear wheels to follow a path inside the tractor's front wheels during a turn, requiring wider turns and extra clearance.

The outward sweep of the rear of a long vehicle during a turn, which can strike nearby objects, pedestrians, or vehicles if not allowed for.

A combination in which a powered tractor unit tows a semi-trailer through a fifth-wheel coupling, articulated so the units pivot separately.

The total distance traveled from the moment a hazard is seen until the vehicle stops, combining perception distance, reaction distance, and braking distance.

The gap kept behind the vehicle ahead; heavy vehicles need at least one second per ten feet of vehicle length plus an extra second at higher speeds.

Choosing a safe speed based on road, weather, traffic, and load conditions, staying below the posted limit when conditions require.

The safety margin kept around the vehicle on all sides so there is room to react and maneuver if another road user makes a mistake.

Areas around a large vehicle that the driver cannot see in the mirrors; other drivers lingering there are a major collision risk.

Setting mirrors so the driver can see the sides and rear of the vehicle and trailer, checked before every trip and after coupling.

Federal rules limiting driving time and requiring rest periods for commercial drivers, tracked in a log or electronic logging device.

An electronic system that automatically records driving time and engine data to help drivers comply with hours-of-service rules.

Physical or mental tiredness that impairs judgment and reaction time; drivers must rest rather than push through drowsiness.

Cargo that poses risks such as fire, explosion, or toxicity; it requires special placards, handling, and often a hazardous materials endorsement.

A diamond-shaped warning sign placed on vehicles carrying hazardous materials, identifying the hazard class to emergency responders and the public.

An intersection where a road crosses train tracks; drivers must slow, look both ways, and never stop on the tracks.

Loss of tire traction on a slippery surface; the driver should ease off the accelerator and steer in the direction the vehicle needs to go rather than brake hard.

A condition in which tires ride on a film of water and lose contact with the road, reducing steering and braking control at higher speeds.

An entrance or exit connecting a highway to another road; drivers must adjust speed to the ramp's curve and posted advisory speed.

A crash in which the vehicle tips onto its side or roof; high center of gravity, speed in curves, and abrupt steering are common causes.

A sequence confirming that the air brake system holds pressure, does not leak excessively, and that warning signals operate correctly.

The measured thickness of rubber above the tire's wear indicators; minimum legal depth must be maintained on steering and other tires.

Connecting the tractor to the trailer, including locking the fifth wheel, attaching air lines and electrical cords, and raising the landing gear.