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CDL glossary
The English words you will see on the test, explained. Tap a card to flip it.
All ·
281
General Knowledge
Air Brakes
Combination Vehicles
Doubles and Triples (T)
Tank Vehicles (N)
Hazardous Materials (H)
Passenger (P)
School Bus (S)
Skills test guide
CMV
General Knowledge · Flip ↻
Commercial motor vehicle: a truck or bus that needs a CDL.
GVWR
General Knowledge · Flip ↻
Gross vehicle weight rating: the loaded weight set by the maker for one vehicle.
GCWR
General Knowledge · Flip ↻
Gross combination weight rating: the rated weight of a power unit plus trailers.
CLP
General Knowledge · Flip ↻
Commercial learner's permit: lets you practice with a qualified CDL holder beside you.
ELDT
General Knowledge · Flip ↻
Entry-level driver training, required from a registered provider before some skills tests.
BAC
General Knowledge · Flip ↻
Blood alcohol concentration. The limit for a CMV driver is 0.04%.
Out-of-service
General Knowledge · Flip ↻
An order that stops a driver or vehicle until the problem is fixed.
Disqualification
General Knowledge · Flip ↻
Loss of the right to drive a CMV for a period of time.
Pre-trip inspection
General Knowledge · Flip ↻
A full check of the vehicle before driving, often taught as seven steps.
Tread depth
General Knowledge · Flip ↻
Minimum 4/32 inch on front tires and 2/32 inch on others.
Lug nuts
General Knowledge · Flip ↻
Nuts that hold the wheel. Rust streaks around them can mean they are loose.
Leaf spring
General Knowledge · Flip ↻
Part of the suspension. Missing or broken leaves are a defect.
Reflective triangles
General Knowledge · Flip ↻
Warning devices you set out when stopped on the road. You need three.
Double clutching
General Knowledge · Flip ↻
Shifting by releasing the clutch in neutral between gears.
Downshift
General Knowledge · Flip ↻
Shifting to a lower gear, before a hill or curve.
Retarder
General Knowledge · Flip ↻
A device that helps slow the vehicle and reduces brake wear.
Convex mirror
General Knowledge · Flip ↻
A curved mirror with a wider view. Things look smaller and farther away.
Blind spot
General Knowledge · Flip ↻
An area around the vehicle you cannot see in your mirrors.
Following distance
General Knowledge · Flip ↻
At least 1 second per 10 feet of vehicle length; add 1 second above 40 mph.
Perception distance
General Knowledge · Flip ↻
Distance traveled from seeing a hazard until your brain recognizes it.
Reaction distance
General Knowledge · Flip ↻
Distance traveled from recognizing the hazard until your foot hits the brake.
Braking distance
General Knowledge · Flip ↻
Distance traveled from pressing the brake until the vehicle stops.
Traction
General Knowledge · Flip ↻
The grip between the tires and the road.
Black ice
General Knowledge · Flip ↻
A thin, clear layer of ice that makes the road look only wet.
Hydroplaning
General Knowledge · Flip ↻
Tires lose contact with the road and ride on water.
Center of gravity
General Knowledge · Flip ↻
The point where the weight is centered. A high one makes rollover more likely.
Off-tracking
General Knowledge · Flip ↻
Rear wheels follow a shorter path than front wheels in a turn.
Hazard
General Knowledge · Flip ↻
Any road condition or road user that is a possible danger.
Distracted driving
General Knowledge · Flip ↻
Anything that takes your eyes, hands or mind off driving.
Hours of service
General Knowledge · Flip ↻
Federal limits on driving and on-duty time to prevent fatigue.
Crossbuck
General Knowledge · Flip ↻
The X-shaped sign at a railroad crossing.
Escape ramp
General Knowledge · Flip ↻
A ramp on steep grades to stop runaway vehicles.
Brake fade
General Knowledge · Flip ↻
Loss of braking power from overheated brakes.
Counter-steer
General Knowledge · Flip ↻
Turning the wheel back after an evasive turn to stay in control.
Stab braking
General Knowledge · Flip ↻
Brake fully, release when wheels lock, re-apply when they roll (no ABS).
Controlled braking
General Knowledge · Flip ↻
Brake as hard as you can without locking the wheels.
Blowout
General Knowledge · Flip ↻
A sudden tire failure. Hold the wheel firmly and stay off the brake.
Skid
General Knowledge · Flip ↻
When tires lose grip. The most common cause is over-braking.
Jackknife
General Knowledge · Flip ↻
The trailer swings out and folds toward the tractor.
Placard
General Knowledge · Flip ↻
A diamond sign on the vehicle that identifies hazardous materials.
Shipping papers
General Knowledge · Flip ↻
Documents that describe the cargo, required for hazmat.
Tie-down
General Knowledge · Flip ↻
Chain, strap or other device used to secure cargo.
Header board
General Knowledge · Flip ↻
A front-end board that protects you from cargo shifting forward.
Blocking and bracing
General Knowledge · Flip ↻
Pieces placed against cargo to stop it from moving.
Air compressor
Air Brakes · Flip ↻
Pumps air into the storage tanks.
Governor
Air Brakes · Flip ↻
Controls when the compressor pumps air: cut-out about 125 psi, cut-in about 100 psi.
Air tank drain
Air Brakes · Flip ↻
Valve that removes water and oil from the tanks.
Alcohol evaporator
Air Brakes · Flip ↻
Puts alcohol into the air to reduce ice in cold weather.
Safety valve
Air Brakes · Flip ↻
Opens at 150 psi to protect the tanks from too much pressure.
Foot valve
Air Brakes · Flip ↻
The brake pedal, also called the treadle valve.
S-cam
Air Brakes · Flip ↻
An S-shaped cam that forces the brake shoes against the drum.
Slack adjuster
Air Brakes · Flip ↻
Links the push rod to the camshaft. More than about 1 inch of play needs adjustment.
Brake chamber
Air Brakes · Flip ↻
The part where air pushes the push rod to apply the brakes.
Supply pressure gauge
Air Brakes · Flip ↻
Shows the air pressure in the tanks.
Application pressure gauge
Air Brakes · Flip ↻
Shows how much air you are applying to the brakes.
Low air pressure warning
Air Brakes · Flip ↻
Light or buzzer that must come on before tank pressure falls below 55 psi (check your state manual).
Wig wag
Air Brakes · Flip ↻
A mechanical arm that drops into view when air pressure is low.
Spring brakes
Air Brakes · Flip ↻
Held off by air; come on by spring force when pressure drops to 20–45 psi.
Dual air brake system
Air Brakes · Flip ↻
Two separate air systems (primary and secondary) with one set of controls.
Leakage rate
Air Brakes · Flip ↻
Air lost per minute; checked with brakes released and applied.
Brake lag
Air Brakes · Flip ↻
Delay of about half a second for air to reach the brakes.
ABS
Air Brakes · Flip ↻
Anti-lock braking system; keeps wheels from locking in hard braking.
Wheel chocks
Air Brakes · Flip ↻
Blocks placed against tires to keep a parked vehicle from rolling.
Fifth wheel
Combination Vehicles · Flip ↻
The coupling plate on the tractor that the trailer rests on.
Kingpin
Combination Vehicles · Flip ↻
The pin under the trailer that locks into the fifth wheel jaws.
Locking jaws
Combination Vehicles · Flip ↻
Close around the shank of the kingpin.
Landing gear
Combination Vehicles · Flip ↻
Legs that support the front of an uncoupled trailer.
Glad hands
Combination Vehicles · Flip ↻
Couplers that connect the service and emergency air lines.
Service line
Combination Vehicles · Flip ↻
The control or signal line, often blue.
Emergency line
Combination Vehicles · Flip ↻
The supply line, often red. Losing it applies the trailer emergency brakes.
Tractor protection valve
Combination Vehicles · Flip ↻
Keeps air in the tractor if the trailer breaks away or leaks badly.
Trailer air supply
Combination Vehicles · Flip ↻
Red eight-sided knob. Push in to supply air; pull out to apply trailer emergency brakes.
Trailer hand valve
Combination Vehicles · Flip ↻
Also trolley valve or Johnson bar. Use only to test trailer brakes.
Relay valve
Combination Vehicles · Flip ↻
Lets the trailer brakes apply more quickly.
Dummy couplers
Combination Vehicles · Flip ↻
Keep dirt and water out of air lines that are not connected.
Shut-off valves
Combination Vehicles · Flip ↻
Cut-out cocks. Open, except at the back of the last trailer.
Converter dolly
Combination Vehicles · Flip ↻
A gear with a fifth wheel used to connect a second trailer.
Rearward amplification
Combination Vehicles · Flip ↻
Crack-the-whip effect: the last trailer is most likely to roll over.
Bobtail
Combination Vehicles · Flip ↻
A tractor driving without a trailer. Can be hard to stop smoothly.
Crossed air lines
Combination Vehicles · Flip ↻
Service and emergency lines connected the wrong way; test the trailer brakes.
Cut-out pressure
Air Brakes · Flip ↻
Tank pressure (about 125 psi) at which the governor stops the compressor from pumping.
Cut-in pressure
Air Brakes · Flip ↻
Tank pressure (about 100 psi) at which the governor lets the compressor pump again.
Service brake
Air Brakes · Flip ↻
The brake system you apply with the brake pedal in normal driving.
Emergency brake
Air Brakes · Flip ↻
System that uses parts of the service and parking brakes to stop the vehicle if the brakes fail.
Treadle valve
Air Brakes · Flip ↻
Another name for the brake pedal (foot valve) in an air brake system.
Foundation brakes
Air Brakes · Flip ↻
The brakes at each wheel, such as S-cam drum, wedge or disc brakes.
Brake drum
Air Brakes · Flip ↻
Round part at each axle end that the wheel bolts to; shoes press inside it to stop.
Brake lining
Air Brakes · Flip ↻
Friction material on the brake shoes or pads.
Push rod
Air Brakes · Flip ↻
Rod pushed out of the brake chamber by air; it moves the slack adjuster.
Wedge brakes
Air Brakes · Flip ↻
Brakes where the push rod drives a wedge between two shoes to spread them.
Disc brakes
Air Brakes · Flip ↻
Air brakes that use a power screw to clamp a rotor between caliper pads.
Power screw
Air Brakes · Flip ↻
Part in air disc brakes that clamps the rotor, like a large C-clamp.
Front brake limiting valve
Air Brakes · Flip ↻
Old (pre-1975) valve that cut front brake air by half on "slippery"; keep it on "normal."
Stop light switch
Air Brakes · Flip ↻
Electric switch worked by air pressure that turns on the brake lights.
Modulating control valve
Air Brakes · Flip ↻
Dash lever that applies the spring brakes gradually if the service brakes fail.
Dual parking control valves
Air Brakes · Flip ↻
Valves (often on buses) that use a separate tank to release spring brakes a few times in an emergency.
Primary system
Air Brakes · Flip ↻
Half of a dual air system; usually works the rear axle brakes.
Secondary system
Air Brakes · Flip ↻
Half of a dual air system; usually works the front axle brakes.
Automatic slack adjuster
Air Brakes · Flip ↻
Slack adjuster that adjusts itself during full brake applications; required since 1994 but must still be checked.
Fanning the brakes
Air Brakes · Flip ↻
Stepping on and off the brake pedal to lower air pressure during the air brake check.
Brake lag distance
Air Brakes · Flip ↻
Distance traveled while air flows to the brakes; about 32 feet at 55 mph.
ECU
Air Brakes · Flip ↻
Electronic control unit of the ABS, found under the vehicle.
Wheel speed sensor
Air Brakes · Flip ↻
ABS sensor at the wheel that tells the computer a wheel is about to lock.
Snub braking
Air Brakes · Flip ↻
Downhill technique: brake to about 5 mph below safe speed (about 3 seconds), release, repeat.
Air storage tanks
Air Brakes · Flip ↻
Tanks (reservoirs) that hold compressed air for the brakes.
Crack-the-whip
Combination Vehicles · Flip ↻
The whip-like swing of the rear trailer after a quick steering move; it can roll the last trailer.
Trailer jackknife
Combination Vehicles · Flip ↻
A skid where locked trailer wheels make the trailer swing out; fix it by releasing the brakes.
Lowboy
Combination Vehicles · Flip ↻
A low-slung trailer that can get stuck on raised railroad crossings.
Possum-belly
Combination Vehicles · Flip ↻
A livestock trailer with a low, dropped belly; can hang up on raised crossings.
Trolley valve
Combination Vehicles · Flip ↻
Another name for the trailer hand valve (Johnson bar); applies only the trailer brakes, for testing.
Cut-out cocks
Combination Vehicles · Flip ↻
Another name for shut-off valves at the rear of trailers that tow other trailers.
Glide plate
Combination Vehicles · Flip ↻
The flat plate under the trailer nose that rests on the fifth wheel; holds the kingpin.
Sliding fifth wheel
Combination Vehicles · Flip ↻
A fifth wheel that can move forward or back on the tractor; must be locked with all pins in place.
Safety latch
Combination Vehicles · Flip ↻
The catch that holds the fifth wheel locking lever in the lock position.
Pintle hook
Combination Vehicles · Flip ↻
A hook on the towing unit that holds the round eye of a trailer or dolly drawbar.
Drawbar
Combination Vehicles · Flip ↻
The tow bar of a trailer or dolly, ending in an eye that couples to a pintle hook or ball.
Gooseneck hitch
Combination Vehicles · Flip ↻
A ball hitch mounted in a truck bed; the trailer coupler clamps over it.
Safety chains
Combination Vehicles · Flip ↻
Chains linking trailer and tow vehicle as a backup; required by law on all trailers.
Breakaway brake switch
Combination Vehicles · Flip ↻
A switch with a lanyard that applies trailer brakes if the trailer separates.
ABS malfunction lamp
Combination Vehicles · Flip ↻
Yellow lamp on the left side of a trailer or dolly that shows the unit has ABS and reports faults.
Converter gear
Doubles and Triples (T) · Flip ↻
Another name for a converter dolly.
Double bottom
Doubles and Triples (T) · Flip ↻
A rig with two trailers (a set of doubles).
Petcock
Doubles and Triples (T) · Flip ↻
A small drain valve on the dolly air tank; open it to release dolly brakes, close it after coupling.
Dead axle
Doubles and Triples (T) · Flip ↻
An axle with no engine power; doubles and triples pull many, raising skid risk.
Endorsement
General Knowledge · Flip ↻
A letter added to a CDL that allows a special vehicle or cargo (T, N, P, H, X, S).
Restriction
General Knowledge · Flip ↻
A code on a CDL that limits what you may drive (for example L = no air brakes).
Interstate commerce
General Knowledge · Flip ↻
Driving across state or national lines, or carrying cargo/passengers on a trip that crosses them.
Intrastate commerce
General Knowledge · Flip ↻
Driving only inside one state, with no part of the trip or cargo crossing state lines.
Excepted
General Knowledge · Flip ↻
Driving only in activities that do not require a federal medical certificate.
Non-excepted
General Knowledge · Flip ↻
Driving that requires a current medical examiner's certificate. Most interstate drivers.
Self-certification
General Knowledge · Flip ↻
Your statement to the state about which of the four types of commerce you drive in.
Medical Examiner's Certificate
General Knowledge · Flip ↻
The "DOT card" (MCSA-5876) from a National Registry examiner; valid up to 24 months.
Medical variance
General Knowledge · Flip ↻
An FMCSA waiver or exemption for a medical condition; shown with the V code.
National Registry
General Knowledge · Flip ↻
The FMCSA list of certified medical examiners allowed to do DOT physicals.
Training Provider Registry
General Knowledge · Flip ↻
The FMCSA list of schools allowed to give ELDT.
Implied consent
General Knowledge · Flip ↻
By driving a CMV you have already agreed to alcohol testing.
Serious traffic violation
General Knowledge · Flip ↻
Offenses like speeding 15+ mph over, reckless driving, following too closely; 2 in 3 years = 60 days.
Out-of-service order
General Knowledge · Flip ↻
An order stopping a driver or vehicle; violating one means disqualification.
Drug and Alcohol Clearinghouse
General Knowledge · Flip ↻
FMCSA national database of CDL drug and alcohol testing violations (since 2020).
CDLIS
General Knowledge · Flip ↻
Commercial Driver's License Information System: links all states' CDL records.
Hardship license
General Knowledge · Flip ↻
A limited license for necessity; never allowed for driving a CMV while suspended.
Security threat assessment
General Knowledge · Flip ↻
The TSA background check (fingerprints, records) required for the H endorsement.
After-trip inspection
General Knowledge · Flip ↻
A check at the end of the trip or day, often with a written vehicle condition report.
DVIR
General Knowledge · Flip ↻
Driver vehicle inspection report: written report of defects found on the vehicle.
Spring hanger
General Knowledge · Flip ↻
A bracket that holds a leaf spring to the frame; cracks or movement are defects.
Torque rod
General Knowledge · Flip ↻
A suspension rod that keeps the axle in position.
Tie rod
General Knowledge · Flip ↻
A steering part that connects the front wheels.
Steering wheel play
General Knowledge · Flip ↻
Free movement before the wheels turn; more than 10 degrees (about 2 in. on a 20-in. wheel) is too much.
Lock ring
General Knowledge · Flip ↻
A ring that holds a tire on a split rim; bent or cracked rings are dangerous.
Valve stem
General Knowledge · Flip ↻
The tube used to fill a tire with air; cuts or cracks are a defect.
Retread
General Knowledge · Flip ↻
A tire with new tread added; not allowed on the front wheels of a bus.
Splash guards
General Knowledge · Flip ↻
Mud flaps behind the wheels; must be present and not drag or rub tires.
Interaxle differential lock
General Knowledge · Flip ↻
A control that locks the two drive axles together for traction.
Governor cut-out
General Knowledge · Flip ↻
The air pressure (about 120–140 psi) where the compressor stops pumping.
Synchronized transmission
General Knowledge · Flip ↻
A manual transmission that matches gear speeds for you, so double clutching is not needed.
Tachometer
General Knowledge · Flip ↻
Gauge that shows engine speed in revolutions per minute (rpm).
Progressive shifting
General Knowledge · Flip ↻
Shifting where the upshift rpm gets higher as you move up through the gears.
Auxiliary transmission
General Knowledge · Flip ↻
An extra gearbox that gives more gear ratios, usually controlled by a knob or switch on the gearshift.
Multi-speed rear axle
General Knowledge · Flip ↻
A drive axle with two or more gear ranges for extra gears.
Engine braking
General Knowledge · Flip ↻
Slowing the vehicle with engine resistance in a low gear; strongest near governed rpm.
Total stopping distance
General Knowledge · Flip ↻
Perception distance + reaction distance + braking distance; at least 419 ft at 55 mph.
Wet ice
General Knowledge · Flip ↻
Ice that is slightly melting; much more slippery than dry ice.
Four-way emergency flashers
General Knowledge · Flip ↻
All turn signals flashing together; used when stopped or moving very slowly.
Emergency warning devices
General Knowledge · Flip ↻
Reflective triangles placed within 10 minutes when stopped on or beside a road.
Tailgating
General Knowledge · Flip ↻
Following another vehicle too closely.
Overhead clearance
General Knowledge · Flip ↻
The space between the top of your vehicle and objects above it, like bridges or wires.
Work zone
General Knowledge · Flip ↻
A road construction or maintenance area; speeding is the top cause of injury and death there.
Maximum Safe Speed
General Knowledge · Flip ↻
A posted sign (often on downgrades) showing a speed you must never exceed.
Blind side
General Knowledge · Flip ↻
The right side of the vehicle, where the driver sees the least, especially when backing.
Move-over law
General Knowledge · Flip ↻
A state law requiring drivers to slow down and, if safe, change to a lane not next to a stopped emergency vehicle or work zone.
Drop-off
General Knowledge · Flip ↻
A sharp drop in height at the edge of the pavement that can tilt a vehicle.
Foreign objects
General Knowledge · Flip ↻
Things that have fallen on the road and can damage tires, rims, and brake or electrical lines.
Slow-moving vehicle symbol
General Knowledge · Flip ↻
A red triangle with an orange center shown on slow vehicles like farm or construction machines.
Conflict
General Knowledge · Flip ↻
A situation where you must change speed and/or direction to avoid hitting someone.
Physical distraction
General Knowledge · Flip ↻
A distraction that takes your hands off the wheel or eyes off the road.
Mental distraction
General Knowledge · Flip ↻
A distraction that takes your mind off driving, such as a conversation or daydreaming.
Hand-held mobile telephone use
General Knowledge · Flip ↻
Holding a phone to talk, dialing by pressing more than one button, or leaving your belted seated position to reach a phone.
Hands-free
General Knowledge · Flip ↻
A phone setup you can use without holding it, such as an earpiece, speakerphone or voice dialing.
Texting
General Knowledge · Flip ↻
Manually entering text into, or reading text from, an electronic device (SMS, e-mail, instant messages, web pages).
Safety-critical event
General Knowledge · Flip ↻
A crash, near-crash or unintended lane departure.
Civil penalty
General Knowledge · Flip ↻
A money fine; up to $2,750 per driver violation and up to $11,000 for employers under the phone/texting rules.
Aggressive driving
General Knowledge · Flip ↻
Driving in a selfish, bold or pushy way without regard for the rights or safety of others.
Road rage
General Knowledge · Flip ↻
Driving with intent to harm others, or physically assaulting a driver or vehicle.
Glare
General Knowledge · Flip ↻
Bright light that can blind you for a short time; recovery can take several seconds.
Fatigue
General Knowledge · Flip ↻
Physical or mental tiredness that, like alcohol, impairs vision and judgment.
Drowsy driving
General Knowledge · Flip ↻
Driving while sleepy; a leading cause of crashes. The only safe cure is sleep.
Corrective lenses
General Knowledge · Flip ↻
Glasses or contact lenses; if your license requires them, driving without them is illegal.
Low beams
General Knowledge · Flip ↻
Dimmed headlights; you can see about 250 feet ahead.
High beams
General Knowledge · Flip ↻
Bright headlights; you can see about 350–500 feet. Dim within 500 feet of other vehicles.
Clearance lights
General Knowledge · Flip ↻
Lights that show the width and height of a large vehicle.
Winterfront
General Knowledge · Flip ↻
A cover on the front grille that reduces cold air to the radiator; if closed too tightly the engine can overheat.
Radiator shutters
General Knowledge · Flip ↻
Slats in front of the radiator that control air flow; if they freeze shut the engine can overheat.
Carbon monoxide
General Knowledge · Flip ↻
A poisonous gas from exhaust leaks that causes sleepiness and can kill.
Tire chains
General Knowledge · Flip ↻
Chains put on drive tires for traction in snow and ice; carry extra cross-links.
Wet brakes
General Knowledge · Flip ↻
Brakes soaked by water; they can be weak, uneven or grab, causing lockups, pulling or jackknife.
Bleeding tar
General Knowledge · Flip ↻
Tar that rises to the road surface in very hot weather, making very slippery spots.
Radiator cap
General Knowledge · Flip ↻
The cap on the pressurized cooling system; never remove it until the system has cooled.
Coolant recovery container
General Knowledge · Flip ↻
A see-through tank that lets you check coolant while the engine is hot.
Passive crossing
General Knowledge · Flip ↻
A railroad crossing with no lights, bells or gates; the driver decides alone.
Active crossing
General Knowledge · Flip ↻
A railroad crossing with flashing lights, bells and/or gates.
Advance warning sign
General Knowledge · Flip ↻
Round black-on-yellow sign before a railroad crossing.
DOT number (crossing)
General Knowledge · Flip ↻
ID number posted at a rail crossing; give it when reporting an emergency.
Over-braking
General Knowledge · Flip ↻
Braking so hard the wheels lock; a cause of skids.
Over-steering
General Knowledge · Flip ↻
Turning the wheels more sharply than the vehicle can turn.
Over-acceleration
General Knowledge · Flip ↻
Giving the drive wheels so much power that they spin.
Skid pad
General Knowledge · Flip ↻
Practice area for learning skid control.
B:C extinguisher
General Knowledge · Flip ↻
Fire extinguisher for electrical fires and burning liquids.
A:B:C extinguisher
General Knowledge · Flip ↻
Extinguisher that also works on wood, paper and cloth.
Controlled substance
General Knowledge · Flip ↻
A drug regulated by law; being under its influence on duty is prohibited.
Hazard class
General Knowledge · Flip ↻
One of 9 hazmat groups (e.g., 1 explosives, 3 flammable, 8 corrosives).
Identification number
General Knowledge · Flip ↻
4-digit hazmat code, after UN or NA, used by first responders.
ERG
General Knowledge · Flip ↻
Emergency Response Guidebook from U.S. DOT; lists hazmat and ID numbers.
ORM-D
General Knowledge · Flip ↻
Other Regulated Material–Domestic, e.g., hair spray, charcoal.
Axle weight
General Knowledge · Flip ↻
Weight one axle or set of axles puts on the ground.
Tire load
General Knowledge · Flip ↻
Maximum safe weight a tire can carry at a set pressure; printed on the sidewall.
Bridge formula
General Knowledge · Flip ↻
Rule allowing less weight on axles that are closer together.
Aggregate working load limit
General Knowledge · Flip ↻
Total rated strength of all tie-downs; must be at least half the cargo weight.
Headache rack
General Knowledge · Flip ↻
Another name for the front-end header board that protects the driver.
False bulkhead
General Knowledge · Flip ↻
Movable wall used to keep a partial load (e.g., livestock) bunched together.
Dry bulk
General Knowledge · Flip ↻
Loose dry cargo in a tank (e.g., grain, cement); high center of gravity.
Oversized load
General Knowledge · Flip ↻
Over-length, over-width or overweight load needing special permits.
Tank vehicle
Tank Vehicles (N) · Flip ↻
A vehicle hauling liquid or gas in tanks over 119 gal each and 1,000 gal total; needs the N endorsement.
Liquid surge
Tank Vehicles (N) · Flip ↻
Movement of liquid in a partly filled tank that pushes the vehicle.
Bulkhead
Tank Vehicles (N) · Flip ↻
A solid wall that divides a tank into smaller tanks.
Baffle
Tank Vehicles (N) · Flip ↻
A bulkhead with holes that slows front-to-back surge.
Smooth bore tank
Tank Vehicles (N) · Flip ↻
A tank with no baffles inside, often used for food such as milk.
Outage
Tank Vehicles (N) · Flip ↻
Space left in a tank so the liquid can expand.
Proper shipping name
Hazardous Materials (H) · Flip ↻
The official name shown in regular (Roman) type in the Hazardous Materials Table.
Packing group
Hazardous Materials (H) · Flip ↻
Roman numeral I, II or III showing the degree of danger for packaging.
Reportable quantity (RQ)
Hazardous Materials (H) · Flip ↻
Amount of a hazardous substance in one package that must be reported if spilled.
Shipper’s certification
Hazardous Materials (H) · Flip ↻
Signed statement that the shipment was prepared according to the rules.
Bulk packaging
Hazardous Materials (H) · Flip ↻
A single container over 119 gallons (liquid), over 882 lb (solid) or over 1,000 lb water capacity (gas).
Cargo tank
Hazardous Materials (H) · Flip ↻
Bulk packaging permanently attached to a vehicle; loaded and unloaded on the vehicle.
Portable tank
Hazardous Materials (H) · Flip ↻
Bulk packaging not permanently attached; loaded and unloaded off the vehicle.
Safe haven
Hazardous Materials (H) · Flip ↻
Approved place to leave a vehicle loaded with explosives unattended.
Transport index
Hazardous Materials (H) · Flip ↻
Number on Radioactive II/III labels showing how much control is needed; total per vehicle 50 or less.
Poison inhalation hazard (PIH)
Hazardous Materials (H) · Flip ↻
Material dangerous to breathe; always needs POISON GAS/POISON INHALATION HAZARD placards.
Marine pollutant
Hazardous Materials (H) · Flip ↻
Chemical toxic to sea life; bulk packages show a white triangle with a crossed-out fish.
Consignee
Hazardous Materials (H) · Flip ↻
The business or person a shipment is delivered to.
Technical name
Hazardous Materials (H) · Flip ↻
Recognized chemical name required with generic (G) shipping names.
Uniform Hazardous Waste Manifest
Hazardous Materials (H) · Flip ↻
Hand-signed shipping paper that must travel with hazardous waste.
CHEMTREC
Hazardous Materials (H) · Flip ↻
Chemical Transportation Emergency Center, 24-hour line (800) 424-9300.
National Response Center
Hazardous Materials (H) · Flip ↻
24-hour federal line (800) 424-8802 for reporting serious hazmat incidents.
Non-ferrous
Hazardous Materials (H) · Flip ↻
Metal with no iron; required (or non-metal) for 1.1–1.3 floor liners.
Passenger endorsement
Passenger (P) · Flip ↻
The P endorsement on a CDL, needed to drive a bus for 16 or more people including the driver.
Standee line
Passenger (P) · Flip ↻
A 2-inch floor line (or other marking); standing riders must stay behind it, never forward of the rear of the driver's seat.
Hazard label
Passenger (P) · Flip ↻
A 4-inch diamond-shaped label showing the hazard class of a material; there are 9 kinds.
Brake-door interlock
Passenger (P) · Flip ↻
Transit bus system that applies the brakes and holds the throttle at idle while the rear door is open.
Roof hatch
Passenger (P) · Flip ↻
An emergency exit in the bus roof; some may be locked partly open for air.
Charter bus
Passenger (P) · Flip ↻
A bus hired by a group for a trip; riders should board only at departure time.
Danger zone
School Bus (S) · Flip ↻
Area around a school bus where children are most at risk: up to 30 ft in front, 10 ft at the sides and rear.
Flat mirror
School Bus (S) · Flip ↻
Outside mirror at the front corners; should show 200 ft (4 bus lengths) behind, the sides and the rear tires.
Crossover mirror
School Bus (S) · Flip ↻
Front-corner mirror showing the area directly in front of the bus and the service door area.
Stop arm
School Bus (S) · Flip ↻
The stop signal arm that swings out from the bus side when the red lights are on.
Crossing control arm
School Bus (S) · Flip ↻
An arm on the front bumper that swings out so crossing students must walk farther ahead of the bus.
Alternating flashing lights
School Bus (S) · Flip ↻
Amber lights warn of a coming stop (at least 200 ft before); red lights mean the bus is stopped and loading.
Handrail hang-up
School Bus (S) · Flip ↻
When clothing, straps or body parts get caught in the handrail or door as a student exits.
Post-trip inspection
School Bus (S) · Flip ↻
Walk-through and walk-around after the route to find students, left items, open windows/doors, problems and damage.
Containment area
School Bus (S) · Flip ↻
Space beyond the tracks needed to fully clear them; rule of thumb: bus length plus 15 ft.
Tail swing
School Bus (S) · Flip ↻
The rear of the bus swinging out the opposite way in a turn; up to 3 ft on a school bus.
Strobe light
School Bus (S) · Flip ↻
Roof-mounted white flashing light used when visibility is limited.
Lookout
School Bus (S) · Flip ↻
A person who warns the driver of obstacles, people and vehicles while backing, without giving backing directions.
Evacuation
School Bus (S) · Flip ↻
Getting all students off the bus to a safe place; mandatory for fire, a stall at a rail crossing, a shifting bus, imminent collision or a hazmat spill.
Three points of contact
Skills test guide · Flip ↻
Two hands and one foot (or two feet and one hand) touching the vehicle when climbing in or out.
Unsafe act
Skills test guide · Flip ↻
A dangerous action during a skills test, such as not setting the parking brake; it can cause automatic failure.
Encroachment
Skills test guide · Flip ↻
Touching or crossing an exercise line or cone with any part of the vehicle (except mirrors and high special parts).
Pull-up
Skills test guide · Flip ↻
Pulling forward during a backing exercise to correct position; extra pull-ups are errors.
Look
Skills test guide · Flip ↻
Getting out, opening the door, or leaving your seat to check the vehicle's position during backing.
Final position
Skills test guide · Flip ↻
Where the vehicle must end up at the end of a backing exercise, inside the boundaries.
Straight-line backing
Skills test guide · Flip ↻
Basic control exercise: backing straight through an alley of cones.
Offset backing
Skills test guide · Flip ↻
Basic control exercise: backing from one lane into a parallel alley and stopping in a 3-foot box.
Unsafe coasting
Skills test guide · Flip ↻
Being out of gear (clutch down or in neutral) for more than the length of the vehicle.
Sight glass
Skills test guide · Flip ↻
A small clear window on a reservoir that shows the fluid level.
Rust trails
Skills test guide · Flip ↻
Rust streaks from lug nuts or rims that can show they are loose.
Cotter pin
Skills test guide · Flip ↻
A split metal pin that keeps a nut or bolt from coming loose.
U-bolt
Skills test guide · Flip ↻
A U-shaped bolt that clamps the springs to the axle.
Apron
Skills test guide · Flip ↻
The flat plate under the front of a semi-trailer, around the kingpin, that rests on the fifth wheel.
Drawbar ring
Skills test guide · Flip ↻
The ring (eye) on the trailer tongue that couples into a pintle hook.
Breakaway cable
Skills test guide · Flip ↻
A cable that applies the trailer brakes if the trailer separates.
Tandem release
Skills test guide · Flip ↻
The lever and pins that lock a sliding trailer axle group in place.
DEF
Skills test guide · Flip ↻
Diesel Exhaust Fluid, a liquid used to clean diesel exhaust; it has its own tank and dash light.