Colorado CDL General Knowledge flashcards

32 cards. Read the term and the definition here. The deck at the top of this page is optional.

Class A CDL threshold

A combination vehicle with a gross combination weight rating over 26,000 pounds, including a towed unit over 10,000 pounds, requires a Class A commercial driver's license.

Total stopping distance

Sum of perception distance, reaction distance, and braking distance. Braking distance grows with the square of speed, so faster speeds greatly lengthen the total.

Following distance rule

Allow at least one second per ten feet of vehicle length, plus one second above 40 mph. A 60-foot vehicle needs six seconds below 40 mph.

Railroad crossing stop zone

Vehicles carrying passengers or hazardous materials must stop between 15 and 50 feet from the nearest rail, then look and listen before crossing.

Steer tire tread minimum

Front steer tires on a commercial vehicle must have at least 4/32 inch of tread depth; all other tires require at least 2/32 inch.

CMV alcohol limit

A commercial driver with a blood alcohol concentration of 0.04 percent or higher is disqualified. Refusing a required chemical test also triggers disqualification.

Colorado rural interstate speed

Many rural interstate highways in Colorado are posted at 75 mph, urban areas commonly at 65 mph, and two-lane highways generally at 55 mph unless posted otherwise.

Engine braking on grades

Select a lower gear before descending a long grade and use engine braking to hold speed, avoiding continuous service brake use that causes overheating and fade.

Air pressure build-up test

With the engine at operating rpm, air pressure should rise from 85 to 100 psi within 45 seconds. A slower rise indicates a compressor or leak problem.

Static air leak limit

With the engine off and the system fully charged, pressure loss must not exceed 3 psi per minute for a single vehicle or 4 psi per minute for a combination.

Applied air leak limit

With the brake pedal held fully down, leakage must not exceed 4 psi per minute on a single vehicle or 6 psi per minute on a combination vehicle.

Low-air warning threshold

The low-air warning buzzer and light must activate before pressure falls below 60 psi. Spring brakes must fully apply between 20 and 45 psi.

Governor cut-out pressure

The governor stops compressor output at roughly 120 to 140 psi and restarts it near 100 psi. The safety valve releases near 150 psi.

Slack adjuster push test

With brakes released, push the slack adjuster by hand. Travel beyond about 1 inch on a standard chamber indicates the brakes need adjustment or repair.

Brake fade cause

Continuous service brake use on a long downgrade overheats the drums and reduces friction. Lower gears and intermittent braking preserve braking capacity.

Wet tank drain valve

The wet tank collects moisture and oil from the compressor. Drain it daily, along with the primary and secondary tanks, to prevent contamination and freeze-ups.

Fifth-wheel tug test

After coupling, set the trailer brakes and pull the tractor gently forward. The trailer should not move if the locking jaws are closed around the kingpin.

Trailer air line colors

The emergency or supply line is typically red and the service line is blue. Crossed lines cause trailer brakes to lock or fail to release properly.

Off-tracking definition

The rear wheels of a combination vehicle follow a shorter path than the front wheels, so turns require swinging wide and checking mirrors for the trailer's rear.

Rearward amplification

The whipping effect that grows toward the rear of a multi-trailer combination. It increases with speed and makes triple trailers most prone to rollover.

Trailer sway response

If the trailer begins to fishtail, release the accelerator and steer straight ahead. Hard braking during sway can worsen the oscillation and cause a jackknife.

Landing gear check

Landing gear must be fully raised before driving. Contact with the road damages the gear and can destabilize the trailer during turns or bumps.

Placard weight threshold

Placards are required when 1,001 pounds or more aggregate gross weight of a hazard class is loaded. Bulk packages require placards regardless of weight.

Hazard class number 3

Class 3 covers flammable and combustible liquids. Class 2 is gases, Class 8 is corrosives, and Class 9 is miscellaneous hazardous materials.

Shipping paper placement

Hazardous materials shipping papers must be within the driver's reach while seated, kept in a marked holder, and include the basic description and emergency phone number.

Hazmat endorsement requirement

An H or X endorsement requires a TSA security threat assessment, a knowledge test, and a valid medical certificate. The background check must be renewed.

Hazmat parking distance

Do not park a placarded vehicle within 5 feet of the traveled portion of a road, and never near an open flame, bridge, or crowded place unless attended.

Hazmat smoking rule

Smoking and open flames are prohibited within 25 feet of a vehicle carrying explosives, oxidizers, or flammable materials. Shut off the engine during fueling.

Liquid surge effect

In a partially filled tank, liquid shifts forward when braking and rearward when accelerating, lengthening stopping distance and raising rollover risk.

Baffle function

Baffles divide a tank into compartments to slow liquid movement. Baffled tanks still surge, so smooth braking and gentle steering remain necessary.

Tanker rollover risk

A tanker has a higher center of gravity than a dry van, so it tips at lower lateral acceleration. Slow down in curves and on ramps.

Tank vehicle endorsement

An N endorsement is required to drive a tank vehicle carrying more than 1,000 gallons. Hazardous materials in a tanker also require an H or X endorsement.