Iowa CDL General Knowledge Test key terms

The total ground covered from the moment a hazard is seen until the vehicle comes to a complete stop, combining perception distance, reaction distance, and braking distance.

The distance a vehicle travels while the driver's eyes and brain recognize that a hazard exists ahead, before any physical action is taken.

The distance traveled between the moment a driver decides to act and the moment the foot actually reaches and presses the brake pedal or accelerator.

The distance a vehicle travels from the instant the brakes are applied until it stops, affected by speed, weight, brake condition, and road surface traction.

The gap a driver keeps behind the vehicle ahead, measured in seconds by counting after that vehicle passes a fixed object; one second per ten feet of vehicle length plus one.

The safety margin of clear space kept around a commercial vehicle so that a sudden stop, lane change, or evasive move by others does not force a collision.

A planned path of travel, such as an empty lane or shoulder, that a driver identifies in advance and can use if the space ahead closes suddenly.

The skill of scanning far ahead and to the sides to spot developing problems, such as merging traffic, road work, or brake lights, before they become emergencies.

Continuously searching the roadway 12 to 15 seconds ahead of the vehicle, and checking mirrors regularly, to identify changing conditions early enough to respond smoothly.

A routine glance at both flat and convex mirrors, done every few seconds and before any turn, lane change, or stop, to confirm what is beside and behind the vehicle.

An area alongside or behind a commercial vehicle that cannot be seen in the mirrors, where a car may hide; drivers must know its size and check by turning the head.

The large areas around a truck or bus, including front, rear, and both sides, where other drivers cannot see the commercial driver or be seen in the mirrors.

A systematic walk-around check of tires, brakes, lights, fluids, coupling devices, and cargo securement performed before driving to confirm the vehicle is safe and legal.

A three-part check of a vehicle's air brake system covering leakage rate, low-air warning activation, and spring brake pop-out, done during the pre-trip inspection.

A light and buzzer that must activate before air pressure drops below 60 psi, warning the driver that braking power is being lost and the vehicle must be stopped safely.

A parking brake held released by air pressure; when pressure falls too low, heavy springs apply the brakes automatically, bringing the vehicle to a controlled stop.

Loss of braking power caused by overheating the brakes through repeated or prolonged use, common on long downgrades; controlled by gearing down and using intermittent braking.

A device that uses engine compression to slow the vehicle without using the service brakes, helping prevent brake fade on long or steep downgrades.

The engine-driven pump that builds and maintains air pressure in the brake system; it must recover pressure quickly enough to keep the vehicle safely operable.

A mechanical or spring-applied brake, separate from the service brakes, used to hold a parked vehicle in place and available as an emergency stopping aid.

The combination of fifth wheel, kingpin, locking jaws, and safety latch that connects a tractor to a semitrailer; it must be inspected and pull-tested before driving.

The horseshoe-shaped plate on the tractor that locks onto the trailer kingpin, supporting the front of the semitrailer and allowing it to pivot during turns.

The vertical pin mounted under the front of a semitrailer that is gripped by the fifth wheel locking jaws to hold the trailer to the tractor.

After coupling, the driver tugs the tractor forward gently with the trailer brakes set to confirm the fifth wheel jaws are locked and will not release.

The tendency of the rear wheels of a long vehicle or trailer to follow a shorter path than the front wheels, so turns must be made wider to keep the trailer off curbs.

The extra space the front and rear corners of a vehicle sweep through during a turn; a driver must allow for it to avoid hitting poles, signs, or nearby vehicles.

The technique for turning right in a large vehicle: check mirrors, signal early, swing wide while staying in the proper lane, and watch the trailer's rear wheels clear the corner.

Choosing the correct transmission gear for the road speed and load, keeping the engine in its power band and using a lower gear on downgrades to control speed.

A shifting method for non-synchronized manual transmissions: press the clutch, shift to neutral, release, press again, then engage the next gear to match speeds.

Moving up or down through the gears one at a time in order rather than skipping gears, which is required in many heavy transmissions to avoid damage.

Any activity that pulls attention from the road, such as phone use, eating, adjusting a GPS, or reading a map; texting and handheld phone use are prohibited for commercial drivers.

Physical or mental tiredness that slows reaction time and judgment; drivers must rest, follow hours-of-service limits, and stop when drowsy rather than push on.

Operating after dark, when visibility drops and glare from oncoming headlights impairs vision; drivers should slow down, dim lights for traffic, and watch for unlit hazards.

Loss of tire traction on a slippery surface; the driver should stop braking, steer in the direction the vehicle needs to go, and avoid sudden corrections.

A condition where tires ride on a thin film of water and lose contact with the pavement, causing loss of steering and braking control; slow down in heavy rain.

The use of tiedowns, straps, chains, and blocking to keep cargo from shifting or falling; the system must meet minimum working load limits and be checked during the trip.

A strap, chain, cable, or rope used with an anchor point and tensioning device to hold cargo to the vehicle; the required number depends on cargo length and weight.

Placing cargo so that axle and gross weight limits are not exceeded and the load stays balanced, since too much weight on one axle or side harms steering and braking.

The maximum weight allowed on a single axle or axle group, set by law; exceeding it is illegal and can cause tire failure or loss of control.

A diamond-shaped warning sign placed on a vehicle carrying regulated hazardous materials, showing the hazard class and identifying the load to emergency responders.

The bill of lading or manifest listing the hazardous materials aboard, including proper shipping name, class, and quantity; it must be kept within reach and shown to authorities.

A reference carried by hazardous materials drivers that lists protective actions, evacuation distances, and first aid for each hazard class in an incident.