CDL Audio Study Guide

Stopping distance

Total stopping distance is three things added together: perception distance, reaction distance, and braking distance. At highway speed a large vehicle can take the length of a football field or more to stop, so leave plenty of room.

Following distance

Use one second of following distance for every ten feet of vehicle length at speeds under forty miles per hour. Above forty, add one more second. A sixty-foot combination needs at least seven seconds of space.

Downgrades and brake fade

On a long downgrade, your main brake is a low gear, not the brake pedal. Riding the brakes overheats them and causes brake fade, where they stop working. Pick your low gear before you start down.

Skids and blowouts

If a tire blows out, hold the wheel firmly, stay off the brake, and let the vehicle slow before easing off the road. To stop a braking skid, get off the brake so the wheels roll again, then steer where you want to go.

Alcohol

For a commercial driver the legal limit is a blood alcohol level of point zero four percent, half the limit for a regular driver. Any detectable alcohol can put you out of service.

Wet roads

Slow down when it rains. Hydroplaning, where your tires ride on a film of water, can start at speeds as low as thirty miles per hour when there is standing water.

The governor

The air compressor is controlled by the governor. It stops pumping, called cut out, at about one hundred twenty-five pounds per square inch, and starts again, called cut in, at about one hundred pounds.

Low air warning

The low air pressure warning light and buzzer must come on before pressure drops below sixty pounds per square inch. If it comes on, stop and park safely as soon as you can.

Spring brakes

If pressure keeps falling, the spring brakes come on automatically, usually between twenty and forty-five pounds. That is why you never wait once the low air warning starts.

The leak test

With the engine off and brakes released, a single vehicle should lose less than two pounds of air per minute, and a combination less than three. With the brakes pushed and held, the limits are three and four.

Draining tanks

Water and oil collect at the bottom of the air tanks and must be drained. If tanks have automatic drains, still check them. Water can freeze and knock out your brakes in cold weather.

Stopping distance

Air brakes add a little brake lag, about half a second before they take hold, on top of perception and reaction distance. Plan for the extra room.

Coupling

The fifth wheel jaws must close fully around the trailer kingpin, and the locking lever must be in place. Check the connection by pulling forward gently in low gear against the locked trailer brakes.

The trailer hand valve

The trailer hand valve, sometimes called the trolley valve, is only for testing. Never use it for parking, because the air could leak out and release the brakes. Always use the parking brakes to hold a parked rig.

Off-tracking

When you turn, the rear trailer wheels follow a tighter path than the tractor. This off-tracking means you must swing wide enough that the trailer clears curbs, poles, and other vehicles.

Rollover

A loaded trailer has a high center of gravity and rolls over easily. Keep the cargo low and centered, and take ramps and curves well below the posted car speed.

Glad hands

The air lines connect at the glad hands. Keep the service and emergency lines matched correctly, and keep the seals clean so they do not leak.

The endorsement

To get the hazmat endorsement you must pass the knowledge test and complete a Transportation Security Administration background check, including fingerprinting. The test alone is not enough.

When to placard

Most hazardous materials require placards once you are carrying one thousand one pounds or more in total. The most dangerous materials, in Table 1, require placards in any amount.

Placard placement

Placards go on all four sides of the vehicle, front, rear, and both sides, and must be readable from each direction. The shipper provides the placards and the shipping papers.

Shipping papers

Hazmat shipping papers must be within your reach while driving, usually in a pouch on the door, and on the driver's seat when you step out of the cab.

Smoking and parking

Never smoke within twenty-five feet of a placarded vehicle carrying flammables or explosives. With explosives, never park within three hundred feet of a bridge, tunnel, building, or open fire.

If it leaks

If your load is leaking, do not touch it and do not try to identify it by smell. Keep people away, and send someone with the shipping papers to get help.

Why inspect

You inspect for safety and because federal rules require it. A problem found in the yard is cheaper and safer than one found on the highway.

Steering play

Free play in the steering wheel should be small, no more than about ten degrees, which is roughly two inches of movement at the rim before the wheels move. More than that is a serious defect.

Tires

Steer tires need at least four thirty-seconds of an inch of tread. Other tires need at least two thirty-seconds. Check for even wear, proper inflation, and no cuts or bulges.

Leaks and fluids

Look under the vehicle for fresh puddles. Check engine oil, coolant, and power steering fluid levels, and look at the belts and hoses in the engine compartment.

Lights and equipment

All required lights and reflectors must work and be clean. You must carry emergency equipment: a charged fire extinguisher, spare electrical fuses unless the vehicle has breakers, and warning triangles.

Shapes

An eight-sided red sign always means stop. A downward triangle means yield. A round yellow sign means a railroad crossing is ahead. A diamond is a warning. A pennant on the left of the road means no passing.

Colors

Red means stop or prohibited. Yellow warns of a hazard ahead. Orange marks construction and work zones. Green gives directions and distances. Blue points to services like fuel and food. Brown marks parks and recreation.

Warning signs for trucks

A truck on a downhill grade sign means pick a low gear now. A low clearance sign means stop if your vehicle is taller than the number shown. A slippery-when-wet sign means slow down and avoid hard braking.

Railroad crossings

The X-shaped crossbuck marks the crossing itself and works like a yield sign. Buses and placarded hazmat vehicles must stop, look, and listen before crossing.

Do not enter and wrong way

A do not enter sign means the road ahead is one-way against you. A wrong way sign, placed farther in, means you are already headed into oncoming traffic. Get off the roadway safely right away.