Following Distance and Stopping

Key points

1. Stopping distance equals reaction distance plus braking distance.

   Source: Handbook p. 40

   “REACTION DISTANCE + BRAKING DISTANCE = STOPPING DISTANCE”
   Iowa Driver's Manual, Handbook p. 40

2. At higher speeds, it takes longer to stop.

   Source: Handbook p. 40

   “At higher speeds, it takes longer to stop.”
   Iowa Driver's Manual, Handbook p. 40

3. Use the 3 to 4 second rule to keep a safe following distance; it only works in normal traffic and good weather.

   Source: Handbook p. 41

   “using the 3- to 4-second rule will help you establish and maintain a safe following distance and provide adequate time for you to brake to a stop if necessary. This rule only works in normal traffic under good weather conditions.”
   Iowa Driver's Manual, Handbook p. 41

4. Beginning drivers should keep at least three seconds under normal conditions.

   Source: Handbook p. 41

   “An inexperienced or beginning driver should maintain at least a three-second following distance under normal driving conditions.”
   Iowa Driver's Manual, Handbook p. 41

5. At 40 mph use 4 to 5 seconds, and 6 or more on slippery roads or when your view is blocked.

   Source: Handbook p. 41

   “At speeds of 40 mph, a four- to five-second following distance is recommended. When road conditions are slippery or the vehicle in front of you blocks your view, a following distance of six or more seconds is recommended.”
   Iowa Driver's Manual, Handbook p. 41

6. Count from when the car ahead passes a landmark; your bumper should not pass it before you count to three.

   Source: Handbook p. 41

   “Watch the vehicle ahead of you pass a landmark, such as a sign, and begin slowly counting. In order to achieve a safe following distance, your front bumper should not pass the landmark before you’ve counted to three.”
   Iowa Driver's Manual, Handbook p. 41

7. To warn drivers behind you of an unexpected stop, tap your brake pedal 3 or 4 times quickly.

   Source: Handbook p. 41

   “tap your brake pedal three or four times quickly. This will let those behind you know you are about to slow down.”
   Iowa Driver's Manual, Handbook p. 41

8. With ABS, press the brake as hard as you can and keep pressing.

   Source: Handbook p. 41

   “Press on the brake pedal as hard as you can and keep pressing.”
   Iowa Driver's Manual, Handbook p. 41

9. You must stop when a visually impaired person with a cane or guide dog is walking in front of or near you.

   Source: Handbook p. 41

   “When a visually impaired person with a cane (often white or red-tipped) or guide dog is walking in front of you”
   Iowa Driver's Manual, Handbook p. 41

Numbers to know

3 questions from the Iowa practice test

1. 1. For a beginning driver in normal conditions, what following gap does the Iowa manual recommend at minimum?

   1. One second, regardless of speed
   2. At least three seconds
   3. Exactly two seconds for every driver
   4. A fixed distance of one car length
   Show answer

   At least three seconds. The three-second minimum applies to an inexperienced or beginning driver under normal driving conditions. It is a time gap, so the physical distance grows as speed increases. An experienced driver may sometimes use two seconds in normal conditions, but that does not replace the beginning-driver recommendation. Slippery roads or blocked visibility call for six or more seconds; the manual measures the gap in seconds, not car lengths. Pick a roadside object, count the seconds after the vehicle ahead passes it, and increase the gap whenever weather, speed, or sight distance worsens.

2. 2. Which following-distance rule is the safest and easiest way to judge space behind another vehicle?

   1. Keep one car length for every five mph
   2. Use the Three-Four Second Rule
   3. Stay exactly two seconds behind in all conditions
   4. Follow close enough to read the vehicle's plate
   Show answer

   Use the Three-Four Second Rule. The Iowa manual identifies the Three-Four Second Rule as the safest and easiest way to judge a following gap. It helps preserve enough room to stop if the vehicle ahead slows suddenly. A car length formula is not the method the manual names, and exactly two seconds is not suitable for every driver or condition. Reading a plate is a visual task, not a safety measure. Choose a stationary landmark, start counting when the lead vehicle passes it, and adjust farther back when weather or visibility reduces the margin.

3. 3. On ice and snow, how much greater can stopping distances be, according to the Iowa manual?

   1. Twice as great
   2. Three times as great
   3. Five times as great
   4. Up to 10 times greater
   Show answer

   Up to 10 times greater. Iowa warns that stopping distances can be as much as 10 times greater on ice and snow. That is why the handbook tells you to begin slowing long before an intersection or turn and to brake only while traveling in a straight line. The three-times figure comes from a different comparison, a car at 60 mph versus one at 30 mph, so it does not describe winter traction. Stay far behind the vehicle ahead so you never need a sudden stop, which can cause skidding.

Source: the Iowa Driver's Manual, Chapter 4: Braking and Stopping. 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.