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 and hydroplane.

   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. At night, how far ahead should low beams allow a driver to see the roadway?

   1. About 25 feet
   2. About 100 feet
   3. About 350 feet
   4. About 1,000 feet
   Show answer

   About 100 feet. The handbook distinguishes the visibility distances produced by the two headlight settings. Low beams allow the driver to see about 100 feet ahead, while high beams extend that distance to about 350 feet. The 350-foot choice belongs to high beams, not low beams. The shorter and longer alternatives do not match the stated equipment guidance. At night, keep speed low enough to stop within the visible distance, dim when meeting or following another vehicle, and watch for unlighted road users.

2. 2. 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.

3. 3. When should you increase the normal following distance behind another vehicle?

   1. Only after the vehicle ahead activates its hazard lights
   2. At high speeds or in bad weather
   3. Only on dry roads when traffic is moving below the limit
   4. Never, if your tires have at least 2/32 inch of tread
   Show answer

   At high speeds or in bad weather. The three-second interval is a minimum starting point, not a universal maximum. Idaho specifically says to increase following distance at high speeds or in bad weather. Rain, ice, snow, and reduced visibility can make braking and judging distance more difficult, while speed increases the distance traveled during reaction time. Waiting for hazard lights is too late, and tire tread does not eliminate the need for a space cushion. Pick a fixed roadside object, count the gap, and add several seconds when conditions call for extra margin.

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.