Vehicle Systems, Hours of Service, and Non-Driving Activities
Vehicle Systems
Air brake system
The compressor charges the tanks; the governor cuts the compressor out near 125 psi and back in near 100 psi. A safety valve protects the system around 150 psi. The wet tank collects moisture and must be drained daily. The system is dual-circuit: if one circuit fails, the other still provides stopping power, which is why a sudden pressure loss is a warning, not an instant catastrophe.
ABS, retarders, and adjustment
ABS prevents wheel lockup and helps you keep steering control; it does not necessarily shorten stopping distance. A pulsing brake pedal during hard braking is normal - hold steady pressure and do not pump. Engine retarders and exhaust brakes help on grades but should be switched off on slippery surfaces, where they can cause drive-wheel skids. Slack adjusters must be checked, and excessive pushrod travel means the brake is out of adjustment.
Engine and electrical
Check coolant only when the engine is cold, and never remove a hot radiator cap. Watch oil pressure, coolant temperature, and the voltmeter or ammeter; a gauge that reads discharge means the charging system is failing. Know the warning signs for low oil pressure, overheating, and a broken belt.
Traps
Questions confuse cut-in and cut-out pressures, claim ABS shortens stopping distance, or say ABS means you should pump the pedal. Others suggest a retarder is helpful on ice.
Rule of thumb
Governor cuts out near 125 psi, cuts in near 100 psi; the low-air warning must come on before 60 psi, and spring brakes apply around 20–45 psi.
Hours of Service
The federal limits
For property-carrying interstate drivers, the core numbers are: 11 hours of driving after 10 consecutive hours off duty; a 14-hour on-duty window that starts when you come on duty and does not pause for meals, fuel, or breaks; a required 30-minute break after 8 cumulative hours of driving; and the 60-hour/7-day or 70-hour/8-day limit, reset by 34 consecutive hours off duty. Sleeper-berth splits let you divide the required 10 hours into 8/2 or 7/3 pairs. Passenger-carrying drivers work under 10-hour driving and 15-hour on-duty limits.
The log
A record of duty status covers a 24-hour period and must show each change of duty status, the location, total hours in each status, and total miles. Records are kept for six months, and an ELD handles most of this automatically. Know the four statuses: off duty, sleeper berth, driving, and on duty not driving.
Traps
The most common error is treating the 11-hour and 14-hour limits as interchangeable. The 14-hour clock keeps running during breaks - only the 30-minute break rule cares about cumulative driving. The break is required after 8 cumulative hours of driving, not 8 hours of being on duty. Another trap: the 34-hour restart is off-duty time, not a long break at a dock.
Worked example
You start at 06:00, drive until 10:00 (4 hours), load for an hour, and drive 11:00–15:00 (4 more hours). You have hit 8 cumulative driving hours, so a 30-minute break is required before any further driving, and your 14-hour window still closes at 20:00 regardless of the break.
Note: California intrastate operations follow state limits that differ from the federal ones; check the current California manual if a question specifies intrastate.
Non-Driving Activities: Fitness, Paperwork, and Conduct
Fatigue and wellness
Fatigue impairs judgment much like alcohol, and only sleep fixes it - coffee and energy drinks merely postpone the crash. Warning signs include yawning, heavy eyelids, drifting in the lane, missing exits, and tailgating without meaning to. Plan trips so you are not driving during hours when you would normally sleep, take real breaks, and treat illness, medication, and untreated sleep apnea as safety issues rather than private ones.
Alcohol and drugs
For a commercial driver the threshold is 0.04% BAC - half the private-driver limit. Refusing a test has consequences of its own. Prescription and over-the-counter drugs count: if a label warns against driving or machinery, you cannot drive. Know that alcohol can remain in your system longer than you feel its effects.
Distraction and devices
California prohibits handheld phone use and texting while driving; a hands-free setup is required for adults, and school bus and passenger drivers face stricter limits. Anything that takes your eyes off the road, including dispatch paperwork, maps, or eating, belongs in a stop, not in a moving lane.
Outside the vehicle
When you leave the cab, set the parking brake, use wheel chocks, and make yourself visible with a high-visibility vest. Use three-point contact on steps and handholds, and watch for traffic and equipment before stepping out. Secure the vehicle against movement whenever it is unattended.
Traps
Questions test 0.04% versus 0.08%, the idea that coffee cures fatigue, and whether hands-free calls are legal (they are for most drivers, but not all). Others assume a parking brake alone is enough on a slope.
Rule of thumb
If you notice two or more fatigue warning signs, stop and rest - do not try to finish the last hour.