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Driving in fog, snow, ice and through water

General Knowledge4 minManual section 2.12, 2.13.2

Fog, slippery roads and deep water all reduce your control. Learn the best advice for fog, how to adjust speed, space, turning and braking on slippery roads, how to spot ice, and how to handle wet brakes.

Fog

Fog can form at any time. It is often unexpected and visibility can get worse very fast. Watch for fog and be ready to slow down. Do not assume fog will thin out after you drive into it.

The best advice for fog is: don't drive in it. It is better to pull off into a rest area or truck stop until visibility improves. If you must drive:

  • Obey all fog-related warning signs.
  • Slow down before you enter fog.
  • Use low-beam headlights and fog lights, even in daytime, and watch for drivers who forgot their lights. (High beams reflect off fog and make it worse.)
  • Turn on your 4-way flashers so drivers coming up behind you notice you sooner.
  • Watch for vehicles on the roadside. Taillights or headlights ahead may not show where the road is; that vehicle may be off the road.
  • Use roadside reflectors as guides to see how the road curves ahead.
  • Listen for traffic you cannot see.
  • Avoid passing.
  • Do not stop on the side of the road unless absolutely necessary.

Driving on slippery roads

  • Slippery surfaces: drive slowly and smoothly. If it is very slippery, you should not drive at all; stop at the first safe place.
  • Start gently and slowly. When you first start, get the feel of the road. Do not hurry.
  • Check for ice, especially on bridges and overpasses. A lack of spray from other vehicles' tires is a sign that the road has iced over. Look at your mirrors and wiper blades too: ice on them usually means ice on the road.
  • Adjust turning and braking. Make turns as gently as you can. Do not brake harder than needed, and do not use the engine brake or speed retarder; they can make the drive wheels skid on slippery roads.
  • Adjust speed. Do not pass slower vehicles unless needed. Go slowly and look far enough ahead to keep a steady speed, avoiding slowing down and speeding up. Take curves slower and do not brake in curves. When it warms up just enough for ice to start melting, the surface becomes even more slippery, so slow down even more.
  • Adjust space. Avoid driving side by side with other vehicles. Leave a longer following distance. If traffic is jammed ahead, slow down or stop until it clears. Try hard to see stops coming early and slow down gradually.
  • Watch for snowplows and salt and sand trucks, and give them plenty of room.

Wet brakes

In heavy rain or deep standing water your brakes get wet. Wet brakes can be weak, apply unevenly, or grab. This can cause loss of braking power, wheel lockups, pulling to one side, and a jackknife if you pull a trailer.

Avoid deep puddles or flowing water if you can. If you cannot:

  • Slow down and put the transmission in a low gear.
  • Gently apply the brakes. This presses the linings against the drums or discs and keeps mud, silt, sand and water out.
  • Raise the engine rpm and drive through, holding light brake pressure the whole way.
  • Once you are through, hold light brake pressure for a short distance so the brakes warm up and dry.
  • Make a test stop when safe: first check that nobody is behind you, then brake to confirm they work properly. If they do not, keep drying them the same way.

Caution: pressing hard on the brake while also giving gas can overheat the drums and linings.

References and scope

The topic reference is listed below. Sources support verification; the lesson itself is here. The current content needs technical and language review before public launch.

Manual reference: 2.12, 2.13.2

Official CDL handbook · Utah ↗StatesOur editorial approach

Put it into practice

Educational questions with explanations. The answer review also works without the interactive quiz.

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Review questions with answers

  1. What is the best advice for driving in fog?
    1. Use high beams so you can see farther
    2. Speed up to get through it quickly
    3. Don't; pull off at a rest area or truck stop until visibility improves
    4. Follow the vehicle ahead closely
    Show answer
    Don't; pull off at a rest area or truck stop until visibility improves

    The best advice is not to drive in fog. Pull off into a rest area or truck stop until visibility is better.

  2. If you must drive in fog, which lights should you use?
    1. Low beams and fog lights, even in daytime
    2. High beams only
    3. Parking lights only
    4. No lights in daytime
    Show answer
    Low beams and fog lights, even in daytime

    Low beams plus fog lights give the best view in fog, even during the day.

  3. Why turn on your 4-way flashers when driving in fog?
    1. To tell others you are about to stop
    2. Because it is required for all trucks at night
    3. To light up the road ahead
    4. So vehicles approaching from behind notice you sooner
    Show answer
    So vehicles approaching from behind notice you sooner

    Four-way flashers give vehicles coming up behind you a quicker chance to notice your vehicle.

  4. In fog, what is a good guide to how the road curves ahead?
    1. The taillights of the vehicle in front
    2. Roadside highway reflectors
    3. The center of your headlight beam
    4. Sounds from other trucks
    Show answer
    Roadside highway reflectors

    Use roadside reflectors to see how the road may curve. Lights ahead may belong to a vehicle that is off the road.

  5. When you enter fog, you should assume it will thin out soon. True or False?
    1. True
    2. False
    Show answer
    False

    False. Do not assume fog will thin out after you enter it. Slow down before entering, and avoid passing.

  6. Which is a sign that ice has formed on the road?
    1. Heavy spray from other vehicles' tires
    2. Wet-looking pavement in the sun
    3. A lack of spray from other vehicles
    4. Salt trucks parked at a rest area
    Show answer
    A lack of spray from other vehicles

    A lack of spray from other vehicles indicates ice has formed. Also check bridges, overpasses, mirrors and wiper blades.

  7. You notice ice building up on your mirrors and wiper blades. This most likely means:
    1. Your heater is broken
    2. The road is probably icy too
    3. You should speed up to warm the engine
    4. The temperature is rising
    Show answer
    The road is probably icy too

    If your mirrors and wiper blades have ice, the road most likely will be icy as well.

  8. On a slippery road, you should NOT use:
    1. Gentle turns
    2. A longer following distance
    3. A steady speed
    4. The engine brake or speed retarder
    Show answer
    The engine brake or speed retarder

    Do not use the engine brake or retarder on slippery surfaces; they can make the drive wheels skid.

  9. When the air warms just enough that ice starts to melt, the road surface becomes:
    1. Even more slippery, so slow down more
    2. Safe to drive at normal speed
    3. Less slippery than dry ice
    4. Better for braking
    Show answer
    Even more slippery, so slow down more

    Melting ice is even more slippery than solid ice, so slow down even more.

  10. On slippery roads you should:
    1. Drive alongside other vehicles for protection
    2. Brake firmly in curves
    3. Keep a longer following distance and avoid driving alongside others
    4. Pass slower vehicles often
    Show answer
    Keep a longer following distance and avoid driving alongside others

    Do not drive alongside other vehicles, keep a longer following distance, and slow down early for traffic jams.

  11. Which problem can wet brakes cause?
    1. Better stopping power
    2. Wheel lockups, pulling to one side, and jackknife with a trailer
    3. Higher engine temperature
    4. Louder horn
    Show answer
    Wheel lockups, pulling to one side, and jackknife with a trailer

    Water in the brakes can make them weak, apply unevenly or grab, causing lack of braking power, lockups, pulling, and jackknife.

  12. If you must drive through deep water, what should you do?
    1. Shift to neutral and coast through
    2. Speed up so you spend less time in the water
    3. Pump the brakes hard the whole time
    4. Slow down, use a low gear, and keep light pressure on the brakes
    Show answer
    Slow down, use a low gear, and keep light pressure on the brakes

    Slow down, use a low gear, gently apply brakes, raise engine rpm and cross with light brake pressure.

  13. Gently applying the brakes while crossing water helps because it:
    1. Presses linings against drums or discs and keeps mud, sand and water out
    2. Cools the brakes down
    3. Locks the wheels for better grip
    4. Raises the trailer
    Show answer
    Presses linings against drums or discs and keeps mud, sand and water out

    Light brake pressure holds the linings against the drums or discs, so mud, silt, sand and water have a harder time getting in.

  14. After you come out of water, what should you do with the brakes?
    1. Nothing; they dry by themselves
    2. Apply hard brake pressure together with the accelerator
    3. Keep light pressure for a short distance, then make a test stop when safe
    4. Pump them as fast as you can
    Show answer
    Keep light pressure for a short distance, then make a test stop when safe

    Keep light pressure on the brakes for a short distance to heat and dry them, then make a test stop. Do not use too much brake and accelerator together.

  15. In fog, you see taillights ahead of you. You should remember that:
    1. They always show exactly where the road is
    2. The vehicle may not be on the road at all
    3. You should follow them closely
    4. You can safely pass that vehicle
    Show answer
    The vehicle may not be on the road at all

    Lights ahead may not be a true indication of the road; the vehicle may be off the road. Watch for vehicles on the roadside.

  16. How should you treat snowplows and salt or sand trucks?
    1. Pass them as quickly as possible
    2. Follow them closely for the cleared lane
    3. Flash your lights so they pull over
    4. Watch for them and give them plenty of room
    Show answer
    Watch for them and give them plenty of room

    Watch for snowplows and salt and sand trucks, and give them plenty of room.