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District of Columbia driving lesson · Weather & Emergency Situations

Fog & night driving

A 3-minute lesson from the District of Columbia course. Read the rules and examples, follow the handbook page references, and check your understanding before you move on.

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Read time
3 minutes
Course unit
Weather & Emergency Situations
Checkpoint questions
6
Source pages
27, 28, 29

At night you can't see as far, as soon or as much, and oncoming headlights cause glare. Fog is like a cloud at ground level. In both, slow down and use lane markings to guide you.

2.5 times

Nighttime fatal crash rate per mile compared with daytime

Handbook p. 27 ↗

Know the rule

Glare makes your pupils contract, and they take time to readjust. Avoid it by glancing back and forth between the side of the road and straight ahead; don't stare at oncoming headlights.

Handbook p. 27 ↗

For safer night driving:

  • Keep your speed low enough to stop within the distance you can see ahead
  • Use quick glances to learn lane positions and the right edge of the road
  • Keep your windshield clean; do not wear sunglasses at night
  • Stay alert; fresh, cool air helps
  • Use the road edge line as a guide; if there is none, use the center line
  • Watch carefully for signs, pedestrians and stopped vehicles
  • Do not stop on the roadway for any reason
  • Carry a red warning light or flares for unavoidable roadside stops
Handbook p. 27 ↗

Fog

A cloud at ground level. It forms when the temperature drops to the dew point and invisible water vapor condenses into suspended water droplets.

Handbook p. 29 ↗
1/4 mile or less

How far fog can reduce visibility

Handbook p. 29 ↗

If you must drive in fog:

  • Reduce speed, and slow even more when you see headlights or taillights ahead
  • Headlights may be a car in the center of the road; taillights may be a car stopped or barely moving
  • Be prepared for an emergency stop
  • Use low beams or fog lights; high beams reflect back and blind you
  • Use the road edge lines or right side of the road as a guide
  • Leave early enough that you don't need to hurry
Handbook p. 29 ↗
10 mph

If fog is so thick you can't go at least this fast, pull completely off the highway

Handbook p. 29 ↗

Know the rule

Yellow pavement markings should always be on your left, never your right. Yellow divides opposing traffic and marks the left edge; white marks the right edge of the roadway.

Handbook p. 29 ↗

Put it into practice

Dense fog rolls in and you can barely see 50 feet. Switch to low beams, slow down and follow the right edge line. If you can't keep up at least 10 mph, pull completely off at a rest area, service station or parking area.

Check your understanding

Read the question, decide on an answer, then open it to check the explanation. These are Roadwise study questions based on the source handbook.

How far can fog reduce visibility, according to the handbook?
  1. To about 3 miles
  2. To about 1 mile
  3. To about 2 miles
  4. To 1/4 mile or less

Answer: To 1/4 mile or less

Fog can reduce visibility to a quarter mile or less, creating hazardous conditions.

Handbook p. 29 ↗
The handbook says to pull completely off the highway if fog is so thick you cannot go at least what speed?
  1. 10 mph
  2. 25 mph
  3. 5 mph
  4. 35 mph

Answer: 10 mph

If fog prevents you from going at least 10 mph, pull completely off the highway or stop at a safe area.

Handbook p. 29 ↗
Which headlight setting should you use when driving in fog?
  1. High beams for maximum visibility
  2. Low beams or fog lights
  3. Parking lights only
  4. No headlights, to avoid glare

Answer: Low beams or fog lights

Use low beams or fog lights in fog; high beams reflect back and reduce your visibility.

Handbook p. 29 ↗
What color are pavement markings that indicate the left travel edge of the roadway, useful in fog or at night?
  1. White
  2. Red
  3. Yellow
  4. Blue

Answer: Yellow

Yellow pavement markings indicate the left travel edge, while white markings denote the right edge.

Handbook p. 29 ↗
Per mile driven, how does the nighttime fatal crash rate compare to the daytime rate, according to the handbook?
  1. About the same
  2. About half as high
  3. About ten times as high
  4. About 2.5 times as high

Answer: About 2.5 times as high

The handbook states the nighttime fatal crash rate is roughly 2.5 times the daytime rate per mile driven.

Handbook p. 27 ↗
Which of these does the handbook tell you NOT to do when driving at night?
  1. Wear sunglasses
  2. Use the road edge line as a guide
  3. Keep your windshield clean
  4. Glance quickly at oncoming lights

Answer: Wear sunglasses

Night driving tips include using the road edge line, keeping the windshield clean and using quick glances; do not wear sunglasses at night.

Handbook p. 27 ↗
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