CDL General Knowledge Test · CDL General Knowledge Test
CDL General Knowledge Test: Night, Fog, Winter, and Hot Weather Concepts
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Overview
This chapter covers driving when you cannot see well or when weather makes the vehicle and road act differently: at night, in fog, in winter, and in very hot weather. In each case you need to slow down and check your vehicle more carefully.
At night, people see less sharply and are blinded by glare. Low beams let you see only about 250 feet ahead, so drive slowly enough to stop within your headlight range. Dim your lights within 500 feet of an oncoming vehicle or one you are following. In fog, the best choice is to pull off and wait. If you must drive, slow down before you enter it, use low beams and fog lights, and avoid passing.
In winter, check coolant, defrosters, wipers, tires, and chains, and watch for black ice, which makes the road look only wet. Bridges freeze before the road. After deep water, keep light pressure on the brakes to dry them. In very hot weather, check tires every 2 hours or 100 miles, never let air out of hot tires, and never remove the radiator cap until the system has cooled.
Key concepts
Dimming headlights
Dim your high beams within 500 feet of an oncoming vehicle and when following another vehicle within 500 feet. Use high beams when it is safe and legal.
Memory tip500 feet, coming or going.
Source: New York State DMV Commercial Driver's Manual (CDL-10), Section 2 · as of 2026
Driving in fog
Pull off to a rest area or truck stop if you can. If you must drive, slow down before entering the fog, use low beams and fog lights, turn on four-way flashers, and avoid passing.
Memory tipLow beams cut through fog. High beams bounce back.
Black ice
A thin layer of ice clear enough to see the road through it, so the road looks wet. Watch for it any time the temperature is below freezing and the road looks wet.
Memory tipFreezing and wet-looking means black ice.
Wet brakes
Water can make brakes weak, uneven, or grabby. After deep water, keep light pressure on the brakes for a short distance to dry them, then make a test stop when it is safe.
Memory tipLight pressure dries them, then test.
Hot weather tires
Inspect tires every 2 hours or every 100 miles in very hot weather. Pressure rises with heat, so do not let air out. If a tire is too hot to touch, stay stopped until it cools.
Memory tipHot tire: wait, do not deflate.
Source: New York State DMV Commercial Driver's Manual (CDL-10), Section 2 · as of 2026
Radiator cap safety
Never remove the radiator cap or any part of the pressurized cooling system until it has cooled. Steam and boiling water can spray out and cause severe burns.
Memory tipIf you cannot touch the cap bare-handed, leave it closed.
Often tested
- Dim your lights within 500 feet of an oncoming vehicle or a vehicle you follow.
- Drive slowly enough to stop within the range of your headlights.
- In fog, use low beams and fog lights, and avoid passing.
- Bridges freeze before the road.
- Never let air out of hot tires.
- Never remove the radiator cap until the system has cooled.
3 sample questions
Verified practice questions from this unit.
Question 1. When should you dim your high beams?
- ① Within 200 feet of an oncoming vehicle
- ② Only when the other driver flashes their lights
- ③ Within 500 feet of an oncoming vehicle, and when following a vehicle within 500 feet
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Answer: ③ Within 500 feet of an oncoming vehicle, and when following a vehicle within 500 feet
Key point: Dim lights within 500 feet
Dim your lights within 500 feet of an oncoming vehicle and when following another vehicle within 500 feet. Use high beams when it is safe and legal.
Wrong choices
- Within 200 feet of an oncoming vehicle: 200 feet is too late. The other driver is already blinded.
- Only when the other driver flashes their lights: You must dim even if they do not flash.
Question 2. If you must drive in fog, which lights should you use?
- ① Low-beam headlights and fog lights
- ② High-beam headlights
- ③ Parking lights only
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Answer: ① Low-beam headlights and fog lights
Key point: Fog: low beams and fog lights
The best advice for fog is to pull off and wait. If you must drive, slow down before you enter the fog, use low beams and fog lights even in daytime, turn on your four-way flashers, and avoid passing.
Wrong choices
- High-beam headlights: High beams reflect off the fog and make it harder to see.
- Parking lights only: Parking lights make you hard for others to see.
Question 3. On a very hot day, your tire pressure reads higher than normal. What should you do?
- ① Let some air out to bring it back to normal
- ② Do not let air out. The pressure will drop when the tire cools.
- ③ Drive faster so air flow cools the tires
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Answer: ② Do not let air out. The pressure will drop when the tire cools.
Key point: Never let air out of hot tires
Air pressure rises with temperature. Do not let air out, or the pressure will be too low when the tire cools. If a tire is too hot to touch, stay stopped until it cools, or it may blow out or catch fire.
Wrong choices
- Let some air out to bring it back to normal: Then the tire will be under-inflated once it cools.
- Drive faster so air flow cools the tires: Higher speed makes tires hotter.