Key facts, numbers, and rules you must know to pass your CDL written test.
The pre-trip inspection is a major test topic. Know the 7-step process and what to check at each step.
Pre-trip steps: (1) Approach vehicle, (2) Engine compartment, (3) Cab check/engine start, (4) Lights check, (5) Walk-around inspection, (6) Check signal lights, (7) Check air brakes
| Item | What to Check |
|---|---|
| Engine oil | Level, no leaks |
| Coolant | Level in sight glass or reservoir |
| Power steering | Fluid level, belt tension |
| Mirrors | Clean, properly adjusted, not cracked |
| Brakes | Pad thickness, no cracks in drums |
| Coupling | 5th wheel properly locked (for combo vehicles) |
Following distance: 1 second per 10 feet of vehicle length at speeds under 40 mph. Add 1 second for speeds over 40 mph. For a 60-foot truck at 55 mph: 7 seconds minimum.
Backing: Always get out and look (G.O.A.L.) before backing. Back to the driver's side whenever possible — you have better visibility.
Double clutching: The standard technique for manual transmission CMVs. Release accelerator → push clutch → move to neutral → release clutch → re-engage clutch → move to target gear.
Retarders: Engine, exhaust, and hydraulic retarders help slow vehicle without using service brakes. Turn off in slippery conditions — they can cause skids.
| Pressure Level | What Happens |
|---|---|
| 100–125 psi | Normal operation |
| ~60 psi | Low air warning (light and buzzer) |
| ~45 psi | Spring brakes activate (emergency) |
| 20–45 psi | Never drive — spring brakes engaged |
Static test: Turn off engine, build to governor cutoff (~125 psi), turn off key, time pressure drop. Should not lose more than 3 psi in 1 minute (single vehicle) or 4 psi in 1 minute (combination).
Brake fade: Caused by overheating from riding brakes downhill. Use engine braking (lower gear) on long downgrades instead.
Crack-the-whip effect: Rear trailers in double/triple combos move faster and can roll over when the front trailer would not. Always reduce speed before curves.
Rear trailer emergency: If rear trailer skids, do NOT brake. Steer to correct the front trailer first. Aggressive braking makes fishtailing worse.
Off-tracking: Rear wheels of a trailer follow a shorter path than front wheels on curves. Allow extra clearance on right turns — the rear wheels cut the corner.
9 HazMat classes: 1-Explosives, 2-Gases, 3-Flammables, 4-Flammable solids, 5-Oxidizers, 6-Poisons, 7-Radioactive, 8-Corrosives, 9-Miscellaneous
Shipping papers: Must be within reach of driver (in door pocket or on seat). Emergency responders need them if there's an accident.
Tunnel restrictions: Some HazMat loads can't go through tunnels. Check the placard and routing before planning your route.
| Rule | Limit |
|---|---|
| Max driving (property) | 11 hours after 10-hour off-duty |
| Max on-duty (property) | 14 hours from start of shift |
| Required rest break | 30-min break after 8 hours driving |
| Weekly limit (60/70 rule) | 60 hrs in 7 days OR 70 hrs in 8 days |
| Sleeper berth split | 8+2 hours (or other qualifying splits) |