Night, fog, rain and flash floods

Key points

1. At night, drive slowly enough to stop within the distance you can see ahead.

   Source: Handbook p. 108

   “always drive slowly enough so you can stop within the distance you can see ahead. This distance is about”
   Idaho Driver's Handbook, Handbook p. 108

2. You can see about 350 feet with high beams and about 100 feet with low beams.

   Source: Handbook p. 109

   “350 feet when using the high beams of your headlights and about 100 feet when using the low beams.”
   Idaho Driver's Handbook, Handbook p. 109

3. Dim headlamps 500 feet before meeting and 200 feet before overtaking another vehicle.

   Source: Handbook p. 43

   “Headlamps must be dimmed 500 feet before meeting and 200 feet before overtaking another vehicle.”
   Idaho Driver's Handbook, Handbook p. 43

4. Turn on headlights in the daytime when vision is 500 feet or less; low beams are best.

   Source: Handbook p. 110

   “You are required to turn on your headlights in the daytime when vision is reduced to 500 feet or less. Low beams are best at such times.”
   Idaho Driver's Handbook, Handbook p. 110

5. Most tires grip wet roads up to 35 mph; at 55 mph they may lose all contact with the road.

   Source: Handbook p. 111

   “At speeds up to 35 miles per hour, most tires grip the road surface even when it's wet. As speed increases, the tires can't grip the road as well. At 55 miles per hour, the tires may lose all contact with the road.”
   Idaho Driver's Handbook, Handbook p. 111

6. Do not use cruise control on wet or icy roads.

   Source: Handbook p. 110

   “For safety reasons, you should not use cruise control if the road is wet and/or icy.”
   Idaho Driver's Handbook, Handbook p. 110

7. Small streams can swell to over 12 inches deep and 80 feet wide in under 5 minutes.

   Source: Handbook p. 112

   “small streams a few feet wide by a few inches deep can swell to over 12 inches deep and 80 feet wide in less than five minutes.”
   Idaho Driver's Handbook, Handbook p. 112

8. Fast moving water 2 feet deep can wash away a vehicle.

   Source: Handbook p. 112

   “Fast-moving water two feet deep can wash away a vehicle”
   Idaho Driver's Handbook, Handbook p. 112

Numbers to know

3 questions from the Idaho practice test

1. 1. How far ahead must Idaho low beams illuminate the roadway?

   1. At least 350 feet
   2. At least 200 feet
   3. At least 100 feet
   4. At least 500 feet
   Show answer

   At least 100 feet. Low beams are required to light the roadway at least 100 feet ahead. The handbook assigns 350 feet to the visibility expected from high beams for people and vehicles, so using that larger number for low beams confuses the two settings. A 200-foot or 500-foot requirement is not the stated low-beam figure. Before driving at night, confirm that the lamps are aimed properly and that the low-beam pattern gives the required forward view without blinding other road users.

2. 2. When must Idaho drivers dim their headlamps before meeting an oncoming vehicle?

   1. Only after the vehicles are side by side
   2. 200 feet before meeting the vehicle
   3. 100 feet before meeting the vehicle
   4. 500 feet before meeting the vehicle
   Show answer

   500 feet before meeting the vehicle. Idaho's lighting rule uses two different distances, so the direction of travel matters. An approaching vehicle must receive low beams beginning 500 feet before the vehicles meet. The 200-foot figure applies when overtaking another vehicle, not when meeting traffic head-on. Waiting until the cars are beside each other risks glare at the exact moment both drivers need clear vision. Remember the pairing: 500 feet for meeting, 200 feet for passing from behind.

3. 3. What speed principle applies when ice, snow, rain, or rough pavement affects the roadway?

   1. The posted limit always permits the same speed
   2. Drive at a reasonable and prudent speed for the conditions
   3. Use the minimum posted speed even when traction is poor
   4. Follow the fastest vehicle to avoid impeding traffic
   Show answer

   Drive at a reasonable and prudent speed for the conditions. Idaho's basic rule requires a speed that is reasonable and prudent at all times, including when the surface, visibility, curves, intersections, or surrounding traffic create additional risk. A posted limit is not a guarantee that full speed is safe. The minimum-speed and fastest-vehicle choices can pressure a driver into going too quickly, while a fixed-limit approach ignores changing conditions. Treat the posted number as an upper boundary and adjust downward whenever the road demands it.

Source: the Idaho Driver's Handbook, Sharing the Road. This lesson is a plain English summary, not the law itself; where it differs, the manual and the statute govern. Last checked 2026-09-27.