Idaho driving lesson · Weather & Special Conditions
Fog, rain, hydroplaning, and flash floods
A 3-minute lesson from the Idaho course. Read the rules and examples, follow the handbook page references, and check your understanding before you move on.
Reduced visibility and water on the road can be as dangerous as ice. It's safest not to drive in fog, dust storms, or heavy rain at all; if you must, slow down and make yourself visible.
Know the rule
You must turn on headlights in daytime when visibility is 500 feet or less. Low beams are best in these conditions.
If conditions get too bad, pull off the road and stop. Don't creep along, and don't use emergency flashers while moving; others may think you're stopped.
Tires riding on a film of water like water skis. Most tires grip wet roads up to 35 mph; at 55 mph they may lose all contact. You can't brake, accelerate, or turn.
A light rain begins after weeks of dry weather. The pavement is at its slickest now, as oil and water mix. Slow down, increase following distance, and turn cruise control off.
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.
At speeds around 55 mph on a wet road, tires may:
only slip on curves
only be affected on gravel roads
grip normally as long as tread is good
lose all contact with the road
Answer: lose all contact with the road
At about 55 mph, tires can hydroplane and lose contact with the road.