For a truck subject to federal tire rules, what minimum major-groove tread depth applies to a tire that is not on a front wheel?
Correct answer: 2/32 inch.
The federal minimum is 2/32 inch for these other tires. The separate front-wheel requirement is 4/32 inch. Measure in a major groove, away from raised tie bars, humps and fillets.
Source: 49 CFR 393.75(c); eCFR title 49 displayed current through September 10, 2026; reviewed September 14, 2026. Also Colorado CDL Manual (06/15/23), page 16. ↗
Two tires in a dual assembly are touching each other. How should you treat this finding?
Correct answer: As a tire defect to resolve before the vehicle is driven.
Dual tires should not rub against each other or vehicle components. Matching size and apparently good tread do not cancel the need to investigate contact and correct the unsafe condition.
Source: Colorado Commercial Driver License Manual (06/15/23), Section 2; 2.1.3 Tire Problems; physical PDF page 16 (printed 16); reviewed September 14, 2026. ↗
Before climbing into a parked truck, which observation deserves investigation?
Correct answer: A fresh fluid puddle under the engine area.
The approach inspection looks for clues such as fresh leaks, damage or an unusual lean, as well as people and obstacles around the vehicle. Investigate a fresh puddle instead of discovering the problem after departure.
Source: Colorado Commercial Driver License Manual (06/15/23), Section 2; 2.1.5 Approaching the Vehicle; physical PDF page 18 (printed 18); reviewed September 14, 2026. ↗
A parking brake fails to hold during its controlled inspection test. What should happen next?
Correct answer: Have the faulty parking brake repaired before operation.
The parking brake must hold the vehicle as intended. A failed test is a defect to fix, not a reason to substitute an improvised parking routine.
Source: Colorado Commercial Driver License Manual (06/15/23), Section 2; 2.1.5 Test Parking Brakes; physical PDF page 22 (printed 22); reviewed September 14, 2026. ↗
Why should a driver pulling a trailer avoid a jerky start?
Correct answer: It can place damaging loads on the coupling and drivetrain.
A smooth, gradual start protects the coupling and other mechanical components and helps maintain control. A harsh surge is not a useful way to test a connection.
Source: Colorado Commercial Driver License Manual (06/15/23), Section 2; 2.2.1 Accelerating; physical PDF page 23 (printed 23); reviewed September 14, 2026. ↗
Before backing a truck into an unfamiliar yard, what should the driver inspect outside the cab?
Correct answer: The full path, including side space and overhead obstructions.
Walk and inspect the intended path before backing. Check the sides, overhead space and surrounding hazards, not just the patch of ground immediately behind the wheels.
Source: Colorado Commercial Driver License Manual (06/15/23), Section 2; 2.2.4 Look at Your Path; physical PDF page 23 (printed 23); reviewed September 14, 2026. ↗
Which truck transmission commonly requires double-clutching to change gears?
Correct answer: An unsynchronized manual transmission.
Most heavy-vehicle unsynchronized manual transmissions use double-clutching. A synchronized manual does not require that technique merely because it is a manual. Learn the system fitted to the actual vehicle.
Source: Colorado Commercial Driver License Manual (06/15/23), Section 2; 2.3.1 Manual Transmissions; physical PDF page 23 (printed 23); reviewed September 14, 2026. ↗
A truck has a retarder acting through the drive wheels. What does the handbook advise when those wheels have poor grip on ice?
Correct answer: Turn the retarder off to avoid provoking a drive-wheel skid.
A retarder can demand more grip than slippery drive tires have available. The handbook advises turning it off on wet, icy or snow-covered roads; understand the vehicle's instructions and use a suitably low speed.
Source: Colorado Commercial Driver License Manual (06/15/23), Section 2; 2.3.4 Retarders; physical PDF page 24 (printed 24); reviewed September 14, 2026. ↗
What is the safer way to use mirrors while a truck is moving on the highway?
Correct answer: Make brief checks and return attention to the road ahead.
Regular, quick mirror checks maintain awareness without leaving the forward road unwatched for too long. Travel continues while the driver's eyes are turned away.
Source: Colorado Commercial Driver License Manual (06/15/23), Section 2; 2.4.2 How to Use Mirrors; physical PDF page 25 (printed 25); reviewed September 14, 2026. ↗
After completing a turn, what should a truck driver do if the turn signal does not cancel itself?
Correct answer: Cancel it so other road users are not misled.
Signal early and through the maneuver, then cancel the signal when the turn is complete. A lingering signal can cause other drivers to predict a turn the truck will not make.
Source: Colorado Commercial Driver License Manual (06/15/23), Section 2; 2.5.1 Turns; physical PDF page 26 (printed 26); reviewed September 14, 2026. ↗
A covered commercial truck is disabled on a rural highway shoulder where warning devices are required. When should the driver place them?
Correct answer: As soon as possible, and no later than 10 minutes.
Ten minutes is an outside deadline, not a suggested delay. Where the requirement applies, place the devices as soon as possible. Necessary traffic stops and the rule's special exceptions are different situations.
Source: 49 CFR 392.22(b)(1); eCFR title 49 displayed current through September 10, 2026; reviewed September 14, 2026. Also Colorado CDL Manual (06/15/23), page 26. ↗
An interstate truck is stopped with fuel leaking near the shoulder. What warning-device choice avoids adding an ignition source near the leak?
Correct answer: Use reflective triangles rather than lighting a flare near the fuel.
Do not introduce a flame where it could ignite leaking flammable liquid or gas. The federal rule prohibits a flame-producing warning at a distance that would not prevent a fire or explosion; reflective triangles avoid that ignition source.
Source: 49 CFR 392.22(b)(2)(vi); eCFR title 49 displayed current through September 10, 2026; reviewed September 14, 2026. Also Colorado CDL Manual (06/15/23), page 27. ↗
Rain has made the pavement slippery but traffic is still moving quickly. What should a truck driver change?
Correct answer: Reduce speed and allow more stopping space for the available traction.
Wet pavement reduces traction and can lengthen stopping distance. Lower speed and additional space give more room to react and stop; a posted maximum is not a guarantee for the weather.
Source: Colorado Commercial Driver License Manual (06/15/23), Section 2; 2.6.2 Slippery Surfaces; physical PDF page 28 (printed 28); reviewed September 14, 2026. ↗
At night, oncoming traffic requires low beams. What should a truck driver do if the visible road becomes shorter than the truck's stopping distance?
Correct answer: Slow enough to stop within the road distance that can be seen.
Speed must fit the available view as well as the road surface. If the truck cannot stop within the illuminated road ahead, reduce speed; another driver's lights are not a reliable substitute.
Source: Colorado Commercial Driver License Manual (06/15/23), Section 2; 2.6.4 Speed and Distance Ahead; physical PDF page 29 (printed 29); reviewed September 14, 2026. ↗
A car is following a truck too closely. Which adjustment helps reduce the need for a sudden stop?
Correct answer: Open more space ahead and make speed changes gradually.
More space ahead lets you slow and react gradually. Signal planned changes early and avoid retaliatory braking or acceleration, which increases risk without controlling the tailgater.
Source: Colorado Commercial Driver License Manual (06/15/23), Section 2; 2.7.2 Dealing with Tailgaters Safely; physical PDF page 30 (printed 30); reviewed September 14, 2026. ↗
Why should a large-truck driver avoid swinging left at the start of a planned right turn?
Correct answer: A following driver may mistake it for a left turn and enter the space on the right.
An early swing left opens a tempting gap on the right and can mislead following traffic. Plan the turn slowly, monitor clearance and traffic, and do not treat the needed turning space as automatic right-of-way.
Source: Colorado Commercial Driver License Manual (06/15/23), Section 2; 2.7.6 Right Turns; Figure 2.13; physical PDF page 31 (printed 31); reviewed September 14, 2026. ↗
