CDL Class A practice test

Answer: 12–15 seconds. The CDL manual says to look 12 to 15 seconds ahead — about a quarter mile at highway speed — so you can spot hazards early.

Answer: 4 seconds. Below 40 mph, leave at least 1 second for every 10 feet of vehicle length: 40 ft ÷ 10 = 4 seconds. Above 40 mph, add 1 more second.

Answer: 5 seconds. 1 second per 10 feet of length (4 seconds) plus 1 extra second for speeds above 40 mph = 5 seconds.

Answer: Perception distance + reaction distance + braking distance. Total stopping distance = perception distance + reaction distance + braking distance. Vehicles with air brakes also add brake lag.

Answer: 30 mph. On a wet road, tires can lose contact and hydroplane at speeds as low as 30 mph, especially with low tire pressure or worn tread.

Answer: Within 10 ft of the rear, 100 ft behind, and 100 ft ahead in the shoulder or lane you are in. On a two-lane or undivided road: one within 10 feet of the rear corner on the traffic side, one about 100 feet behind, and one about 100 feet ahead. On a one-way or divided highway: 10, 100 and 200 feet behind.

Answer: 4/32 inch. The CDL manual's inspection standard is at least 4/32 inch of tread in every major groove on front tires and 2/32 inch on other tires.

Answer: 10 degrees (about 2 inches at the rim of a 20-inch wheel). Steering wheel play of more than 10 degrees — about 2 inches of movement at the rim of a 20-inch steering wheel — can make it hard to steer.

Answer: 0.04%. Federal rules disqualify a CDL holder driving a commercial motor vehicle with a BAC of 0.04% or more — half the usual limit for car drivers.

Answer: Within the first 50 miles. Check cargo and tie-downs within the first 50 miles, then every 3 hours or 150 miles, whichever comes first, and after every break.

Answer: 10 feet of cargo. The CDL manual calls for at least one tie-down for every 10 feet of cargo, and always at least two tie-downs, however small the cargo.

Answer: Before you start down the grade. Shift down before you start the grade. Trying to downshift once speed builds can leave you unable to get into a lower gear.

Answer: Brake firmly until about 5 mph below your safe speed, release, and repeat when you reach the safe speed. Once in the right low gear, apply the brakes hard enough to slow to about 5 mph below your safe speed, then release. When you are back at the safe speed, repeat. Long, light braking overheats the brakes.

Answer: Use the escape ramp. Escape ramps are built to stop runaway vehicles safely. If your brakes fail on a grade, use one.

Answer: Keep the rear of the vehicle close to the curb so others cannot pass on the right, and swing wide as you complete the turn if needed. Turn slowly, keep the rear close to the curb to stop other vehicles passing on your right, and if you must swing wide, do it as you complete the turn.

Answer: Within 500 feet. Use low beams within 500 feet of an oncoming vehicle, and when following another vehicle closely.

Answer: Smaller and farther away than they are. Convex mirrors show a wider area but make things look smaller and farther away than they really are.

Answer: B:C fires. CMVs carry an extinguisher rated B:C, for flammable liquids and electrical fires. Never use water on a fuel or electrical fire.

Answer: Take your foot off the accelerator (and push in the clutch on a manual). For a drive-wheel acceleration skid, stop accelerating so the wheels can roll again, and push in the clutch if you have one so the engine does not keep driving them.

Answer: Sleep. Caffeine, fresh air and music only mask fatigue for a short time. The only cure is sleep.

Answer: It has less traction, so the wheels lock more easily. An empty vehicle has less weight on the tires and so less traction. Stiff suspension and strong brakes can lock the wheels, so stopping can take longer.

Answer: Not move. Pump the brake pedal three times, then press firmly and hold for five seconds. If the pedal moves, there may be a leak or other problem; get it fixed before driving.

Answer: Before you enter the curve. Slow to a safe speed before entering the curve. Braking in a curve can lock the wheels and cause a skid. The posted speed may be too fast for a truck.

Answer: An empty vehicle is taller than a loaded one. Weight compresses the suspension, so a loaded vehicle sits lower. If you passed under a bridge when loaded, you may not clear it empty.

Answer: Between 15 and 50 feet from the nearest rail. When a stop is required, stop within 50 feet but not closer than 15 feet to the nearest rail, then listen and look in both directions.

Answer: Not shift gears. Pick a gear that lets you cross without shifting. Missing a shift on the tracks could stall the vehicle there.

Answer: 14 seconds. The CDL manual says a typical tractor-trailer takes about 14 seconds to clear a single track, and more than 15 seconds for a double track.

Answer: Faster than stopping, if you can do it safely. Top-heavy vehicles can usually steer around a hazard faster than they can stop. Don't brake while turning sharply, or you may skid.

Answer: Avoid braking until your speed has dropped to about 20 mph, then brake gently. Keep one set of wheels on the pavement if you can, avoid braking until speed drops to about 20 mph, then brake gently. Return to the road when it is safe.

Answer: Hold the steering wheel firmly and stay off the brake until the vehicle slows. Hold the wheel firmly, stay off the brakes until the vehicle has slowed, then brake gently, pull off the road and stop.

Answer: No — federal rules prohibit texting and hand-held phone use while driving a CMV. FMCSA rules prohibit CMV drivers from texting and from using a hand-held mobile phone while driving, including while stopped temporarily in traffic. Violations can lead to fines and disqualification.

Answer: The maximum total weight specified by the manufacturer for a single vehicle and its load. GVWR is the manufacturer's maximum loaded weight for a single vehicle. GCWR is the maximum for a combination.

Answer: Only when the engine has cooled. Never remove the radiator cap on a hot engine. Hot coolant under pressure can spray out and cause severe burns.

Answer: Bridges and overpasses. Bridges freeze before the rest of the road because cold air passes above and below them. Be careful when the temperature is near freezing.

Answer: It is thin and clear enough that the road looks only wet. Black ice is a thin layer that is clear enough to see the road underneath, so the road just looks wet. Watch for ice building on mirrors, antennas and wipers.

Answer: Slow down and use low-beam headlights. The best advice is not to drive in fog. If you must, slow down and use low beams; high beams reflect off the fog and make it harder to see.

Answer: Backing toward the driver's side when possible and using a helper. Back toward the driver's side so you can see better, back slowly, and use a helper when you can. Agree on hand signals first.

Answer: Right away, and put out warning devices within 10 minutes. Turn on the four-way emergency flashers when you stop, and place your warning triangles within 10 minutes.

Answer: You are disqualified from driving a CMV, as if you had tested positive. Under implied consent, CDL holders are considered to have agreed to alcohol testing. Refusing leads to disqualification.

Answer: A Hazardous Materials (H) endorsement. Drivers of vehicles carrying hazardous materials that require placards must have the H endorsement, which includes a knowledge test and a TSA security threat assessment.

Answer: Lugging the engine in too high a gear. Climbing in too high a gear lugs the engine and builds heat. Downshift to keep engine speed in the recommended range and watch the temperature gauge.

Answer: 26,001 pounds or more. You need a CDL for a single vehicle with a GVWR of 26,001 pounds or more, or a combination with a GCWR of 26,001 pounds or more.

Answer: 1 year. A first offense such as driving a CMV at .04% BAC or higher, refusing an alcohol test, or leaving the scene of a CMV crash costs your CDL for at least 1 year.

Answer: 3 years. The usual 1-year disqualification rises to at least 3 years when the offense happens in a CMV placarded for hazardous materials.

Answer: Loss of the CDL for life. A second major offense brings a lifetime CDL disqualification.

Answer: 15 mph or more above the posted limit. Serious traffic violations include excessive speeding of 15 mph or more over the limit, reckless driving, improper lane changes and following too closely.

Answer: 60 days. Two serious violations within 3 years mean at least 60 days; three or more within 3 years mean at least 120 days.

Answer: 90 days. The first out-of-service order violation costs at least 90 days; two in 10 years cost at least 1 year; three or more in 10 years cost at least 3 years.

Answer: T. The T endorsement covers double/triple trailers. N is tank, P is passenger, and X is the combined tank and hazardous materials endorsement.

Answer: 4 hours. You may never drink on duty, or drink any intoxicating beverage, regardless of alcohol content, within 4 hours before going on duty.

Answer: One-fourth or more of the leaves are missing. If 1/4 or more of the leaves in any leaf spring are missing, the vehicle is put out of service, though any spring defect can be dangerous.

Answer: It can let poisonous fumes into the cab or sleeper berth. A broken exhaust system can let poison fumes into the cab or sleeper berth. Look for loose, broken, missing or leaking exhaust parts.

Answer: 3 red reflective warning triangles. Required warning devices are 3 red reflective triangles, 6 fuses, or 3 liquid-burning flares, along with a fire extinguisher and spare fuses.

Answer: The nuts are loose. Rust around wheel nuts may mean the nuts are loose, so check their tightness.

Answer: The ABS is not working properly. The ABS light should come on and then go off. If it stays on, the ABS is not working properly.

Answer: Set the parking brake, put the vehicle in a low gear, and gently pull forward against it. With the parking brake set and the vehicle in a low gear, gently pull forward to make sure the brake holds. If it does not hold, get it fixed.

Answer: Defects were noted and certified as repaired, or repairs were not needed. Sign the report only if the defects noted were certified as repaired or not needed. You, not the mechanic, are responsible for the vehicle's safe operation.

Answer: Partly engage the clutch before taking your right foot off the brake. Partly engage the clutch before you take your right foot off the brake, and use the parking brake if needed to keep from rolling back.

Answer: When the road is wet, icy, or snow covered. On poor traction the retarder may cause the drive wheels to skid, so turn it off whenever the road is wet, icy or snow covered.

Answer: Select a low range. Selecting a low range keeps the transmission from shifting up beyond the selected gear and gives greater engine braking on downgrades.

Answer: The trailer(s) are straight. Check mirror adjustment before each trip with the trailer straight, and set each mirror to show part of the vehicle as a reference point.

Answer: It is the best way to keep others from trying to pass you. Signal early, signal continuously until the turn is finished, and cancel the signal afterward. Signaling early keeps others from trying to pass you.

Answer: No; do not direct traffic, because it could cause a crash and you could be blamed. Do not signal other drivers that it is safe to pass. It could cause an accident and you could be blamed.

Answer: Move the rearmost triangle back down the road so warning is provided. Place warning devices back beyond any hill, curve or obstruction that blocks the view within 500 feet, moving the rearmost triangle back.

Answer: 1 3/4 seconds. Average perception time for an alert driver is 1 3/4 seconds. Average reaction time is 3/4 second to 1 second.

Answer: 4 times longer. Doubling speed from 20 to 40 mph makes the impact and the braking distance 4 times greater. Tripling to 60 mph makes them 9 times greater.

Answer: One-third (for example, from 55 to about 35 mph). Wet roads can double stopping distance. Reduce speed by about 1/3 on wet roads, by half or more on packed snow, and to a crawl on ice.

Answer: Water mixes with oil left on the road by vehicles. Right after rain begins, the water mixes with oil left on the road, making it very slippery until continued rain washes the oil away.

Answer: You should always be able to stop within the distance you can see ahead. Always be able to stop within the distance you can see. Fog, rain and night driving with low beams may require you to slow down.

Answer: The engine is near the governed rpm and the transmission is in a lower gear. Use engine braking as the main way to control speed on downgrades. It is strongest near governed rpm in the lower gears.

Answer: Another driver may change lanes into you, and you may be trapped when you need to change lanes. Another driver may suddenly turn into you, and you may have no room when you need to change lanes. Find an open spot away from other traffic.

Answer: Repaving or packed snow may have reduced the clearance since the height was posted. Repaving or packed snow can reduce clearance after the height was posted. If you doubt you can clear, go slowly or take another route.

Answer: Drive a little closer to the center of the road. Some roads make a vehicle tilt toward roadside objects. Where this is a problem, drive a little closer to the center of the road.

Answer: The right turn lane (the outside one). Always take the right lane of two turning lanes. Starting in the inside lane may force you to swing right during the turn.

Answer: The ends of the vehicle may drag or get hung up. Space under a heavily loaded vehicle can be very small. Drainage channels can make the ends of some vehicles drag, so cross carefully.

Answer: A red triangle with an orange center. Slow vehicles such as farm and construction machinery may display the slow moving vehicle emblem, a red triangle with an orange center.

Answer: Car-top luggage and out-of-state license plates. Confused drivers often change direction or stop without warning. Clues to tourists include car-top luggage and out-of-state plates.

Answer: It involves physical and mental distraction at the same time. Texting requires looking at a small screen and using your hands, so it combines physical and mental distraction.

Answer: Give them plenty of room and keep a safe following distance. Give a distracted driver plenty of room and maintain a safe following distance. Be very careful passing, because they may drift in front of you.

Answer: About 250 feet. With low beams you can see about 250 feet ahead, and with high beams about 350 to 500 feet, so drive slowly enough to stop within that range.

Answer: Only half the light they should. Dirty headlights may give only half the light they should, which cuts your vision and makes it harder for others to see you.

Answer: Keep the interior light off and the instrument lights as low as you can while still reading the gauges. A bright cab makes it harder to see outside. Keep the interior light off and dim the instrument lights as low as you can while still reading them.

Answer: Stop driving and sleep for the night or take a 15–20 minute nap. Trying to push on when tired is a major cause of fatal accidents. Stop and go to sleep for the night or take a 15 to 20 minute nap.

Answer: There is no longer any spray coming from other vehicles' tires. A lack of spray from other vehicles indicates ice has formed. Ice on your mirrors or wiper blades is another clue.

Answer: The engine may overheat and stop. Remove ice from the radiator shutters and do not close the winterfront too tightly, or the engine may overheat and stop.

Answer: Use a low gear and keep light pressure on the brakes while crossing. Slow down, use a low gear, and keep light pressure on the brakes to keep water and mud out. Afterward, keep light pressure briefly to dry them and make a test stop.

Answer: Every 2 hours or every 100 miles. In very hot weather, check tire mounting and air pressure every 2 hours or 100 miles.

Answer: A passive crossing. At a passive crossing there are no lights or gates; the decision to stop or proceed is entirely yours. Active crossings have lights, bells and/or gates.

Answer: Round and black-on-yellow. The round, black-on-yellow advance warning sign tells you to slow down, look and listen, and be ready to stop for a train.

Answer: Until the gates go up and the lights have stopped flashing. Stop when the lights begin to flash and before the gate lowers. Remain stopped until the gates go up and the lights stop flashing.

Answer: Get out of the vehicle and away from the tracks. Get out and away from the tracks, then call 911 or the emergency number posted at the crossing and give the location, including the DOT number if posted.

Answer: Overheated brakes that need harder and harder pressure to give the same stopping power. Brakes that get too hot start to fade, so you must press harder and harder for the same stopping power. If you keep braking hard, they can fade until you cannot stop.

Answer: They stop doing their share, so the other brakes overheat and fade. Every brake must do its share. Brakes out of adjustment quit working first, leaving the others to overheat and fade, so check adjustment often.

Answer: They have low-friction parts, streamlined shapes, and stronger engines, so less drag holds them back downhill. The old rule was to use the same gear down as up. Modern trucks have less friction and air drag, so they may need lower gears going down than going up.

Answer: About 3 seconds. Brake hard enough to feel a definite slowdown until you are about 5 mph below your safe speed; this application should last about 3 seconds.

Answer: Countersteer (turn the wheel back the other way). Emergency steering and countersteering are two parts of one action. Be ready to turn back once you pass the obstacle, and do not brake while turning.

Answer: Without anti-lock brake systems (ABS). Stab braking means braking fully, releasing when the wheels lock, and reapplying once they roll. It can only be done without ABS.

Answer: Downshift, pump the brakes, and use the parking brake while looking for an escape route. With lost hydraulic pressure, downshift, pump the pedal, use the separate parking brake carefully, and look for an escape route.

Answer: Drive and brake normally, since you still have regular brakes, and get the system serviced soon. If ABS fails you still have normal brakes. Drive normally, but get the ABS serviced soon.

Answer: Let the vehicle slow down by easing off the turning and braking. In a front-wheel skid the front end keeps going straight no matter how you steer. Stop turning and braking so hard, and slow down without skidding.

Answer: Protect the area so another accident does not happen in the same spot. The first step is to keep another accident from happening there: move your vehicle aside if you can, turn on flashers and set out triangles.

Answer: Not move a severely injured person unless fire or traffic makes it necessary. Do not move a severely injured person unless fire or traffic danger requires it. Stop heavy bleeding with direct pressure and keep the person warm.

Answer: In an open area away from buildings, trees, and other vehicles, but not into a service station. Get off the road and stop in an open area away from anything that might catch fire. Do not pull into a service station, and notify emergency services.

Answer: Keep them shut, because opening them feeds the fire oxygen. Keep the van doors shut, especially with hazardous cargo. Opening them supplies oxygen and can make the fire burn very fast.

Answer: At the source or base of the fire. Stay as far from the fire as possible, position yourself upwind, and aim at the source or base of the fire, not up in the flames.

Answer: Cool it; lots of water may be required. A burning tire must be cooled, and it may take a lot of water. Keep going until whatever was burning has cooled, since it can restart.

Answer: The part that controls judgment and self-control. Alcohol first affects judgment and self-control, which can keep drinkers from knowing they are getting drunk.

Answer: Yes, if the doctor says it will not affect safe driving ability. Possession and use of a drug given by a doctor is allowed if the doctor says it will not affect safe driving. Watch warning labels on all medicines.

Answer: 4 identical placards, on the front, rear, and both sides. A placarded vehicle needs at least 4 identical placards on the front, rear and both sides, readable from all four directions.

Answer: On the driver's seat. Keep hazmat shipping papers in a pouch on the driver's door or in clear view within reach while driving, and on the driver's seat when you are out of the vehicle.

Answer: Contain the product, communicate the risk, and ensure safe drivers and equipment. Hazmat rules exist to contain the product, communicate the risk through papers, labels and placards, and ensure safe drivers and equipment.

Answer: Class 3 – Flammable. Class 3 covers flammable liquids such as gasoline and acetone. Class 8 corrosives include hydrochloric acid and battery fluid.

Answer: Poor traction, so the drive wheels spin easily. Too little weight on the drive axles means poor traction and spinning wheels. Too much weight on the steering axle causes hard steering.

Answer: Hard steering and damage to the steering axle and tires. Overloading the steering axle makes steering hard and can damage the axle and tires; underloading it makes the steering too light to steer safely.

Answer: One-half the weight of the article or group of articles. The combined working load limit of the tie-downs securing an article must be at least one-half times the weight of that article or group of articles.

Answer: To protect people from spilled cargo and to protect the cargo from weather. Covers protect people from spilled cargo and protect cargo from weather. Check covers in your mirrors, since a flapping cover can tear loose.

Answer: That you do not exceed gross weight and axle weight limits. You cannot inspect sealed loads, but you should check that you do not exceed gross weight and axle weight limits.

Answer: It can be a very unstable load with a high center of gravity. Suspended meat can be very unstable with a high center of gravity, so go slowly on sharp curves such as off ramps and on ramps.

Answer: They have a high center of gravity and the load can shift. Dry bulk tanks have a high center of gravity and a load that can shift, so be extremely cautious on curves and sharp turns.

Answer: 45 seconds. With the engine at operating rpm, pressure should rise from 85 to 100 psi within about 45 seconds in dual air systems.

Answer: 125 psi. The governor usually cuts out at about 125 psi and cuts the compressor back in at about 100 psi.

Answer: 150 psi. The safety valve is usually set at 150 psi to protect the tank and system from too much pressure.

Answer: 60 psi. A low-pressure warning signal (light, buzzer or wig-wag) must activate before air pressure drops below 60 psi in the model CDL manual. A few state manuals, such as California's, use 55 psi — use the figure in your state manual.

Answer: 20 to 45 psi. Spring brakes usually apply automatically somewhere between 20 and 45 psi. Stop safely before this happens.

Answer: 2 psi per minute. Brakes released: under 2 psi per minute for a single vehicle, under 3 psi for a combination. Brakes applied (after the initial drop): under 3 psi single, under 4 psi combination.

Answer: 4 psi per minute. For a combination vehicle with the brakes fully applied, leakage should be under 4 psi per minute (under 3 psi for a single vehicle).

Answer: 1 inch. If a slack adjuster moves more than about 1 inch where the push rod attaches, it probably needs adjustment.

Answer: To remove water and compressor oil that can freeze or damage the brakes. Compressed air carries water and oil into the tanks. Drain manually operated tanks at the end of each day so the sludge cannot freeze or ruin brake parts.

Answer: Apply the brakes all the way, release when the wheels lock, and reapply as soon as the wheels start rolling. Stab braking (for vehicles without antilock brakes): brake fully, release when the wheels lock up, reapply once they roll again. Releasing too briefly can keep the vehicle sliding.

Answer: 32 feet. Air takes a moment to flow to the brakes. At 55 mph this brake lag adds about 32 feet to the total stopping distance.

Answer: When the brakes are very hot, or very wet in freezing temperatures. Hot brakes can be damaged by the parking brake, and wet brakes can freeze to the drums in cold weather. Use wheel chocks instead until the brakes cool or dry.

Answer: The primary system usually operates the rear axle(s) and the secondary the front axle (and sometimes one rear axle). Dual systems split the brakes so a failure in one still leaves some braking. Typically the primary system works the regular brakes on the rear axle(s) and the secondary works the front axle.

Answer: Brake fade. Brake fade happens when brakes get too hot. Prevent it by using a low gear and the brakes only in firm applications.

Answer: Antilock braking systems (ABS). Federal rules require ABS on truck tractors with air brakes built on or after March 1, 1997, and on air-braked trailers built on or after March 1, 1998.

Answer: Stop and park safely as soon as possible. Low air warns that the brakes may soon stop working normally and the spring brakes may lock. Stop and safely park while you still have control, then find the leak.

Answer: Reduce the risk of ice in the brake valves and other parts in cold weather. The alcohol evaporator puts alcohol into the air system to help stop water freezing in valves and lines in cold weather. Tanks still need regular draining.

Answer: How much air pressure is in the air tanks. The supply pressure gauge shows tank pressure. An application pressure gauge, if fitted, shows how much pressure you are sending to the brakes.

Answer: Service, parking and emergency brakes. Air brakes combine the service brake (normal stopping), the parking brake, and the emergency brake system, which uses parts of the other two when the service system fails.

Answer: The foot valve (brake pedal). Pressing the brake pedal (foot valve) sends air to the brake chambers. Releasing it lets that air out.

Answer: The S-cam, turned by the slack adjuster and push rod. Air pushes the push rod, which turns the slack adjuster and brake camshaft. The S-cam twists and forces the shoes apart against the inside of the drum.

Answer: Air pressure. Powerful springs apply spring brakes; air pressure holds them back. If air pressure is lost, the springs put the brakes on.

Answer: Applying and releasing the brakes repeatedly, which uses air faster than the compressor can replace it. Each brake application uses air. Fanning (rapidly applying and releasing) can drop air pressure below a safe level.

Answer: Still have normal brakes but no antilock function; get the ABS repaired. ABS is an addition to normal brakes. If it fails, the regular brakes still work normally, but the wheels can lock in hard stops. Get it serviced soon.

Answer: The engine, through gears or a V-belt. The air compressor is driven by the engine through gears or a V-belt, and may be air-cooled or cooled by the engine cooling system.

Answer: Keeps air from flowing back out if the compressor develops a leak. A one-way check valve lets air into the tank but stops it from leaking back out if the compressor or line fails.

Answer: Applying the brakes as hard as you can without locking the wheels, keeping steering wheel movements small. Controlled braking: brake as hard as possible without locking the wheels. If you need to steer or the wheels lock, release and reapply when you can.

Answer: 450 feet. Perception (about 142 ft) + reaction (61 ft) + brake lag (32 ft) + braking (about 216 ft) gives roughly 450 feet — longer than a football field.

Answer: With the parking brake set, gently pull against it in a low gear. Set the parking brake and gently try to pull forward in a low gear. The vehicle should not move.

Answer: Check that they work and drain tanks as your vehicle requires. Automatic drains remove most water and oil, but check that they are working. Manual valves must be drained by hand, usually at the end of each day.

Answer: Low air pressure or brakes out of adjustment. If braking power is poor, check the air pressure and brake adjustment. Brakes out of adjustment are a common cause of weak braking and brake fade.

Answer: The other system still provides some braking, but you should stop safely and get it fixed. The two systems are independent, so one can keep providing some braking if the other fails. Stop safely and have it repaired.

Answer: Normal operating pressure (up to governor cut-out, about 125 psi), with the low-air warning off. Let the pressure build to normal — up to the governor cut-out, about 125 psi — and make sure the low-pressure warning has gone off before moving.

Answer: Before pressure drops below 60 psi. The low air warning must come on before pressure falls below 60 psi (55 psi in a few state manuals, such as California's). Keep fanning: the spring brakes should apply between 20 and 45 psi.

Answer: Air or the engine cooling system. The compressor may be air cooled or cooled by the engine cooling system.

Answer: Check the oil level before driving. A compressor may have its own oil supply or use engine oil. If it has its own supply, check the oil level before driving.

Answer: Turning a quarter turn or pulling a cable. Manual drains are opened by turning a quarter turn or pulling a cable. You must drain these tanks yourself at the end of each day of driving.

Answer: In the bottom of the air tank. Water and compressor oil collect in the bottom of the air tank, which is why each tank has a drain valve at the bottom.

Answer: Every day. Check the alcohol container and fill it as needed every day during cold weather.

Answer: Yes, daily drainage is still needed to get rid of water and oil. An alcohol evaporator reduces ice risk, but daily tank drainage is still needed to remove water and oil unless the system has automatic drains.

Answer: The first tank the air compressor pumps air to. The safety valve sits in the first tank the compressor pumps air to and protects the tank and system from too much pressure.

Answer: Applies more air pressure to the brakes. The brake pedal (foot or treadle valve) controls air pressure: pressing harder applies more pressure, letting up reduces it.

Answer: S-cam drum brake. Foundation brakes are used at each wheel, and the S-cam drum brake is the most common type. Wedge and disc brakes are less common.

Answer: Pushes a wedge directly between the ends of two brake shoes. The wedge is pushed between the ends of the two shoes, forcing them apart and against the inside of the drum.

Answer: A power screw. Air acts on a brake chamber and slack adjuster, which turns a power screw instead of an S-cam.

Answer: A gauge for each half of the system, or one gauge with two needles. A dual system has a gauge for each half of the system, or a single gauge with two needles.

Answer: How much air pressure you are applying to the brakes. The application gauge shows the pressure being applied to the brakes. Not all vehicles have one.

Answer: The brakes are fading, so slow down and use a lower gear. Rising application pressure for the same speed means brake fade. Slow down and use a lower gear.

Answer: Dropping a mechanical arm into the driver's view. A wig wag drops a mechanical arm into your view when system pressure falls too low.

Answer: 80 to 85 psi. Large buses commonly have low-pressure warnings set to signal at 80 to 85 psi.

Answer: An electric switch that works by air pressure. The stop light switch is an electric switch worked by air pressure that turns on the brake lights when you apply the air brakes.

Answer: Cuts normal air pressure to the front brakes by half. In the slippery position, the limiting valve cuts the normal air pressure to the front brakes by half, which reduces stopping power.

Answer: Normal. Front wheel braking is good under all conditions, and front wheel skids from braking are not likely even on ice. Keep the control in normal.

Answer: 60 psi or more. Automatic limiting valves reduce front brake air except during very hard applications of 60 psi or more. The driver cannot control them.

Answer: Air pressure can eventually leak away. Air can leak away over time, so parking and emergency brakes must be held on mechanically, usually by spring brakes.

Answer: The brakes being in adjustment. If brakes are not adjusted properly, neither the regular brakes nor the emergency/parking brakes will work right.

Answer: Yellow, diamond-shaped push-pull knob. Newer vehicles use a yellow, diamond-shaped push-pull knob to control the parking (spring) brakes.

Answer: The combined forces of the springs and air pressure could damage the brakes. Pressing the pedal with the spring brakes on can damage the brakes through the combined force of springs and air. Make it a habit not to do it.

Answer: Apply the spring brakes gradually with a control handle. A modulating valve is a spring-loaded dash control that applies the spring brakes gradually, so you can control them if the service brakes fail.

Answer: Move the lever as far as it will go and hold it with the locking device. To park, move the modulating lever as far as it goes and lock it in place.

Answer: There is only enough air in the separate tank to release the brakes a few times. The separate tank holds only enough air for a few releases, so plan carefully or you may be stopped in a dangerous spot.

Answer: Check the certification label for the date of manufacture. Check the certification label for the date of manufacture. On older towed units, look under the vehicle for the ECU and wheel speed sensor wires.

Answer: On the left side, at either the front or rear corner. Tractors, trucks, and buses have the lamp on the instrument panel. Trailers have it on the left side, front or rear corner.

Answer: 5 mph. Newer systems show the lamp briefly for a bulb check. On older systems it could stay on until you are driving over 5 mph.

Answer: ABS only activates when the wheels are about to lock up. ABS adds to your normal brakes. It does not increase or decrease normal braking ability and works only when wheels are about to lock up.

Answer: 100 psi. Allow time for at least 100 psi to build in both systems, watching both gauges (or needles).

Answer: Either the front or rear brakes will not work fully, so stopping takes longer. With one system low, either the front or rear brakes are not fully operating, so it takes longer to stop. Stop safely and have it fixed.

Answer: The condition and tightness of the compressor drive belt. If the compressor is belt-driven, check that the belt is in good condition and properly tight.

Answer: Release the parking brakes. Release the parking brakes so the slack adjusters can move, with the wheels chocked so the vehicle cannot roll.

Answer: Out-of-adjustment brakes. Out-of-adjustment brakes are the most common roadside inspection problem, so check the slack adjusters.

Answer: Automatic slack adjusters. Vehicles built since 1994 have automatic slack adjusters, which still must be checked.

Answer: Take the vehicle to a repair facility as soon as possible. Manually adjusting an automatic adjuster usually masks a mechanical problem. Use it only as a temporary emergency fix and get the vehicle repaired soon.

Answer: One-half the width of the friction area. Drums or discs must not have cracks longer than half the width of the friction area.

Answer: 3 minutes. Single air systems should build from about 50 to 90 psi within 3 minutes. Dual systems should build from 85 to 100 psi within 45 seconds.

Answer: 5 mph. Move forward at about 5 mph and brake firmly. Note any pulling to one side, unusual feel, or delayed stopping.

Answer: When the engine rpm is down close to idle. Control the pedal for a smooth stop and do not push in the clutch until engine rpm is close to idle. When stopped, select a starting gear.

Answer: 1/2 second or more. Hydraulic brakes work instantly, but air brakes take 1/2 second or more for the air to reach the brakes. This delay is brake lag.

Answer: Perception, reaction, brake lag, and braking distance. Perception distance + reaction distance + brake lag distance + braking distance = total stopping distance.

Answer: Chemical changes in the brake lining that reduce friction, and expansion of the brake drums. Overheating changes the lining chemically, reducing friction, and expands the drums so the shoes must travel farther and press with less force.

Answer: They stop doing their share, so the other brakes overheat and fade. Brakes out of adjustment quit doing their share first, overloading the others. Brakes can go out of adjustment quickly when hot, so check often.

Answer: Only a supplement to the braking effect of the engine. Get into the correct low gear first. The brakes only supplement engine braking on a long or steep downgrade.

Answer: 5 mph. Apply the brakes hard enough to feel a definite slowdown, and release them when speed is about 5 mph below your safe speed.

Answer: 3 seconds. Each application, from your safe speed down to about 5 mph below it, should last about 3 seconds.

Answer: Wait until you reach 40 mph, then brake down to 35 mph and release. Do not brake until you reach 40 mph, then slow to 35 mph and release. Repeat until the bottom of the grade.

Answer: The spring brakes do not work on all axles. Spring brakes do not act on all axles, so a heavy vehicle stops slowly. Stop while you still have enough air to use the foot brake.

Answer: Use the brakes lightly while driving in a low gear to heat and dry them. Wet brakes can freeze if set in freezing weather. Dry them by braking lightly in a low gear, and use wheel chocks on a level surface.

Answer: Let up on the brakes, if you can safely do so. Tractor-only ABS helps keep steering control, but watch the trailer and ease off the brakes if it starts to swing out.

Answer: When you always drive a straight truck or combination with working ABS on all axles. The one exception to normal braking: with working ABS on all axles, you can fully apply the brakes in an emergency stop.

Answer: Sudden emergency braking. A failed warning means you could lose air without knowing it, which can cause sudden emergency braking in a single-circuit system.

Answer: Uses parts of the service and parking brake systems to stop the vehicle in a brake system failure. The emergency system is not separate hardware. It uses parts of the service and parking brake systems.

Answer: A tractor pulling triple trailers, especially the last trailer. Rearward amplification makes the last trailer swing most. Triples are the most likely to roll over, then doubles, then a tractor-semitrailer.

Answer: Red. The emergency (supply) line is usually red and the service (control) line is usually blue, to help you avoid crossing them.

Answer: Red eight-sided (octagon) knob. The trailer air supply control is usually a red eight-sided knob. Push it in to supply air to the trailer; pull it out to shut off air and put on the trailer emergency brakes.

Answer: 20 to 45 psi (depending on the manufacturer). The tractor protection valve keeps air in the tractor if the trailer breaks away or leaks badly. It closes automatically when pressure falls to between 20 and 45 psi, depending on the make.

Answer: No — air can leak away and release the brakes; use the parking brakes. Never park using the trailer hand valve. All the air might leak away and the brakes release. Use the parking brakes.

Answer: The trailer is raised slightly when the tractor backs under it. Set the trailer height so the trailer will be lifted slightly as the tractor backs under it. Too high and it may not couple correctly; too low and the tractor may strike the trailer nose.

Answer: That there is no space between them. Use a flashlight to check that there is no space between the upper and lower fifth wheel, and that the locking jaws are closed around the shank of the kingpin, not its head.

Answer: With the trailer brakes locked, pull the tractor gently forward in low gear. The tug test: with the trailer brakes locked, pull gently forward in a low gear to make sure the trailer is locked to the tractor.

Answer: The rear wheels following a different, shorter path than the front wheels in a turn. In a turn, the rear wheels of a combination follow a shorter path than the front wheels. Longer vehicles off-track more, so allow room at corners.

Answer: Release the brakes so the trailer wheels can regain traction. Trailer skids usually come from locked trailer wheels. Release the brakes to let the wheels grip again, and do not use the trailer hand brake to straighten the rig.

Answer: Drive away without working trailer brakes. With crossed lines, supply air goes to the service line. A trailer with spring brakes would stay braked, but an older trailer without spring brakes could be driven away with no trailer brakes.

Answer: Fully raised and the crank handle secured. Raise the landing gear all the way and secure the crank handle in its bracket. Partly raised gear can catch on railroad tracks or bumps.

Answer: It makes firm contact with the ground. Lower the landing gear until it makes firm contact with the ground. Don't lift too much weight off the tractor, which makes it harder to recouple.

Answer: Keep cargo as close to the ground as possible and go slowly around turns. Keep the cargo low and centered, and go slowly around turns and ramps. Posted speeds can be too fast for loaded trucks.

Answer: Steer gently and smoothly. Sudden steering movements are amplified at the rear trailer and can roll it over. Steer gently, and look far enough ahead to avoid sudden moves.

Answer: Put the trailer emergency brakes on. If the emergency (supply) line breaks or the trailer breaks away, the loss of pressure puts the trailer emergency brakes on.

Answer: Locked (after supplying air, pull out the trailer air supply knob). Connect the air lines, supply air to charge the trailer, then pull out the air supply knob so the trailer brakes are locked before you back under it.

Answer: With the trailer brakes released, open the emergency line shut-off at the rear of the last trailer and listen for air. Set the tractor parking brake, supply air to the trailers, open the emergency line shut-off at the back of the last trailer: you should hear air escaping. Then close it and check the service line the same way.

Answer: Charge the trailer, push in the supply knob, then pull it out and gently try to pull forward — the trailer should not move. With the trailer air supply knob pulled out, the trailer emergency brakes should be on. Pull forward gently; the trailer should not move.

Answer: No — braking only the trailer can make it skid. Don't use the trailer hand valve while driving: braking only the trailer can make it skid. Use it to test the trailer brakes, not for normal stops or parking.

Answer: Keep dirt and water out of the air lines. Dummy couplers or a dead-end coupler keep dirt and water out of the lines when they are not connected to a trailer.

Answer: Open on the front trailers and closed on the last trailer. Shut-off valves let air pass through to the next trailer, so they are open on all trailers except the last, where they are closed.

Answer: Next to the tractor. Put the heaviest trailer first, right behind the tractor. A lighter trailer at the rear is less likely to whip and roll over.

Answer: Locked in place, and not so far forward that the cab or frame can strike the trailer or landing gear in turns. Check the slide is locked and positioned so the tractor frame won't hit the landing gear and the cab won't hit the trailer during turns.

Answer: A yellow ABS malfunction lamp on the left side of the trailer. Trailers built on or after March 1, 1998 must have a yellow ABS malfunction lamp on the left side, near the rear corner.

Answer: Lack of grease can cause steering problems from friction between the tractor and trailer. Poor lubrication causes friction between the fifth wheel and trailer that can make steering difficult.

Answer: Can take longer to stop than a fully loaded combination. Bobtail tractors have little weight on the drive axles and can take longer to stop than a loaded tractor-trailer because of reduced traction.

Answer: The ground can support the trailer. Park on firm, level ground that can support the trailer's weight on its landing gear, then chock and secure the vehicle.

Answer: The tractor directly in front of the trailer. Put the tractor directly in front of the trailer, never back under at an angle, which could push the trailer sideways and break the landing gear.

Answer: The tractor protection valve closes and the trailer air supply knob pops out. As pressure falls to 20–45 psi, the tractor protection valve should close, popping the supply knob from 'normal' to 'emergency' and protecting the tractor's air if the trailer leaks.

Answer: Turn wide as you complete the turn. Turning wide as you complete the turn is better than swinging wide to the left before starting, because it keeps drivers from passing you on the right.

Answer: In the opposite direction from where you want the trailer to go. Backing a car or straight truck, you turn the top of the wheel the way you want to go. With a trailer, you turn the wheel in the opposite direction, then turn it back to follow the trailer.

Answer: So you can hear the brakes. Shut the engine off so you can hear the brakes. Apply and release the trailer brakes and listen for them to apply and for air to escape on release.

Answer: Let up on the brakes (if you can safely do so) until you gain control. Trailer-only ABS makes the trailer less likely to swing out. If you lose steering control or start a tractor jackknife, let up on the brakes until you regain control.

Answer: Only to test the trailer brakes. Use the trailer hand valve only to test the trailer brakes. Using it while driving can make the trailer skid.

Answer: Only as long as there is air pressure in the trailer air tank. Trailers without spring brakes have emergency brakes that work from stored air. They hold only as long as there is air in the tank, so always chock the wheels when parking them.

Answer: On the left side, either on the front or rear corner. Trailers have yellow ABS malfunction lamps on the left side, either on the front or rear corner.

Answer: The DOT number, if posted. Check signposts or the signal housing for emergency notification information, and give the crossing location using all identifiable landmarks, especially the DOT number if posted.

Answer: Look under the vehicle for the ECU and wheel speed sensor wires coming from the back of the brakes. For older units it may be hard to tell. Look under the vehicle for the ECU and wheel speed sensor wires coming from the back of the brakes.

Answer: A single-axle tractor pulling a long trailer with its landing gear set for a tandem-axle tractor. A single-axle tractor pulling a long trailer whose landing gear is set for a tandem-axle tractor has reduced clearance and can hang up on raised crossings.

Answer: Drive slowly enough to see obstacles with your headlights before it is too late to change lanes or stop gently. Sudden lane changes can tip a trailer. At night, drive slowly enough to see obstacles in time to change lanes or stop gently.

Answer: Ten times as likely. Piling up cargo raises the center of gravity. Fully loaded rigs are ten times more likely to roll over in a crash than empty rigs.

Answer: All of the brakes on the vehicle, including the trailer(s). The foot brake sends air to all brakes, including the trailers. There is much less danger of a skid or jackknife using just the foot brake.

Answer: Every day. Water and oil buildup can keep the brakes from working right. Drain each tank every day; even with automatic drains, open the drains to make sure.

Answer: Very stiff suspension springs and strong brakes give poor traction and can make the wheels lock up. Large combination vehicles take longer to stop when empty. Stiff springs and strong brakes give poor traction and may cause bouncing, making wheel lockup very easy.

Answer: Turn the crank in low gear a few extra turns to lift some weight off the tractor, without lifting the trailer off the fifth wheel. For a loaded trailer, a few extra turns in low gear take some weight off the tractor. This makes it easier to unlatch the fifth wheel and to couple next time.

Answer: The shank of the kingpin. Look into the back of the fifth wheel to make sure the jaws have closed around the shank of the kingpin, not the head.

Answer: "Normal". Older vehicles may have a lever. The "normal" position is for pulling a trailer, and the "emergency" position shuts off the air and applies the trailer emergency brakes.

Answer: Seeing it in your mirrors. Any time you brake hard, check the mirrors to make sure the trailer is staying where it should be. Once it swings out of your lane, a jackknife is very difficult to prevent.

Answer: It supplies air to the trailer air tanks and controls the emergency brakes. First, the emergency line supplies air to the trailer air tanks. Second, it controls the emergency brakes on combination vehicles.

Answer: With the plug down to prevent moisture from entering it. Hang the electrical cable with the plug down to keep moisture out, and support the lines so they are not damaged while driving the tractor.

Answer: To the driver's side so you can see. Try to back in a straight line. If you must back on a curve, back toward the driver's side so you can see.

Answer: With the tractor frame still under the trailer. Pull forward until the fifth wheel comes out from under the trailer, but stop with the tractor frame under the trailer. This keeps the trailer from falling if the landing gear collapses or sinks.

Answer: The air line connections. If the lines are crossed, supply air goes to the service line instead of charging the trailer tanks, so there is no air to release the spring brakes. Check the air line connections.

Answer: With normal air pressure and parking brakes released, move forward slowly and apply the trailer brakes with the hand control. Move forward slowly and apply the trailer brakes with the hand control (trolley valve), if equipped. You should feel the brakes come on.

Answer: Brake the same way, regardless of whether you have ABS on the tractor, the trailer, or both. Brake as you always have: use only the force needed, brake the same way whether ABS is on the tractor, the trailer or both, and back off if needed to stay in control.

Answer: The fifth wheel just touches the trailer. Back slowly until the fifth wheel just touches the trailer, without hitting it. Then secure the tractor and check trailer height before connecting air lines.

Answer: Control line or signal line. The service line, also called the control line or signal line, carries air controlled by the foot brake or trailer hand brake.

Answer: Properly connected to glad hands, no air leaks, and secured with enough slack for turns. Air lines should be properly connected, free of leaks and damage, and secured with enough slack for turns.

Answer: To stop other drivers from passing you on the right. Steer the front end wide enough to clear the curb, but keep the rear close to the curb so other drivers cannot pass you on the right.

Answer: 3.5 times as easily as a five-axle tractor. Because of rearward amplification, the last trailer of triples can be rolled 3.5 times as easily as a five-axle tractor.

Answer: When you try to put the brakes on. A service line leak may go unnoticed until you brake. Then the leak quickly lowers tank pressure, and if it drops low enough the trailer emergency brakes come on.

Answer: Turning the top of the steering wheel in the direction of the drift. Correct drift immediately. As soon as the trailer gets off the proper path, turn the top of the steering wheel in the direction of the drift.

Answer: Lowest reverse gear. Use the lowest reverse gear and back slowly to avoid hitting the kingpin too hard. Stop when the kingpin is locked into the fifth wheel.

Answer: More than half. The manual states that more than half of truck driver deaths in crashes are the result of truck rollovers.

Answer: That it is not so far forward that the tractor frame will hit the landing gear, or the cab hit the trailer, during turns. Check that all locking pins are present and locked, and that the fifth wheel is not so far forward that the frame hits the landing gear or the cab hits the trailer in turns.

Answer: Lets the air out of the trailer emergency line, causing the trailer emergency brakes to come on. When it closes, the tractor protection valve stops air leaving the tractor and lets air out of the trailer emergency line, so the trailer emergency brakes come on.

Answer: Keeps air in the tractor or truck brake system if the trailer breaks away or develops a bad leak. The tractor protection valve keeps air in the tractor or truck brake system if the trailer breaks away or develops a bad leak.

Answer: Empty or lightly loaded. When trailer wheels lock up, the trailer tends to swing around. This is more likely when the trailer is empty or lightly loaded.

Answer: "Trailer air supply" control valve in the cab. The trailer air supply control valve in the cab lets you open and shut the tractor protection valve.

Answer: To ease pressure on the fifth wheel locking jaws so the release lever is easier to pull. Backing gently eases pressure on the locking jaws. Setting the parking brakes while the tractor pushes against the kingpin holds the rig with pressure off the jaws.

Answer: Tilted down toward the end of the tractor, jaws open, and safety unlocking handle in the automatic lock position. Before coupling, the fifth wheel should be tilted down toward the end of the tractor, jaws open, and the safety unlocking handle in the automatic lock position.

Answer: 1 second for each 10 feet of vehicle length, plus another second if going over 40 mph. Following far enough back lets you avoid sudden steering. Use at least 1 second for each 10 feet of vehicle length, plus another second over 40 mph.

Answer: Begin in the low gear range, then switch to the high gear range once it is free of weight. Use the low gear range (if equipped) to begin raising the landing gear, then switch to high once it is free of weight. Raise it all the way and secure the crank handle.

Answer: The rear trailer is twice as likely to turn over as the tractor. Rearward amplification describes the crack-the-whip effect. A value of 2.0 means the rear trailer is twice as likely to turn over as the tractor.

Answer: Clean the couplers and rubber seals. The rubber seal on each coupler prevents air from escaping. Clean the couplers and rubber seals before making a connection.

Answer: Converter dollies and trailers built before 1975. Newer trailers have spring brakes, but converter dollies and trailers built before 1975 are not required to have them.

Answer: The tractor may strike and damage the trailer nose. The trailer should be raised slightly by the tractor as you back under it. If it is too low, the tractor may strike and damage the trailer nose.

Answer: The emergency (supply) line from the tractor. Each trailer and converter dolly has one or more air tanks. They are filled by the emergency (supply) line from the tractor.

Answer: Trolley valve or Johnson bar. The trailer hand valve, also called the trolley valve or Johnson bar, works the trailer brakes.

Answer: The rear wheels of the last trailer. Longer vehicles off-track more. The rear wheels of the trailer off-track more than the tractor's, and with more than one trailer, the last trailer's rear wheels off-track the most.

Answer: ABS does not necessarily shorten stopping distance, but it helps you keep control during hard braking. ABS only activates when wheels are about to lock up. It does not necessarily shorten stopping distance but helps you keep the vehicle under control.

Answer: So someone else will not move the truck while you are under it. Secure the vehicle: transmission in neutral, parking brakes on, engine off, and take the key so no one moves the truck while you are under it.

Answer: A low-slung unit such as a lowboy or car carrier. Trailers with low underneath clearance can get stuck on raised crossings, including lowboys, car carriers, moving vans and possum-belly livestock trailers.

Answer: The trailer brakes to be applied more quickly than would otherwise be possible. Service line pressure changes with how hard you brake. It is connected to relay valves, which apply the trailer brakes faster than would otherwise be possible.

Answer: Press the two seals together with the couplers at a 90 degree angle to each other. Press the two seals together with the couplers at a 90 degree angle, then turn the glad hand attached to the hose to join and lock them.

Answer: You might push the trailer sideways and break the landing gear. Put the tractor directly in front of the trailer. Backing at an angle might push the trailer sideways and break the landing gear.

Answer: Use wheel chocks to keep the trailer from moving. Air stored in a trailer without spring brakes can leak away and release the brakes. Use wheel chocks to keep it from moving.

Answer: Between the rear of the tractor frame and the landing gear. Check for enough clearance between the rear of the tractor frame and the landing gear so the tractor will not hit the landing gear in a sharp turn. Also check clearance between the tractor tires and the trailer nose.