Following distance, passing and sharing the road

Key points

1. Use the three second rule to check your following distance; it works at any speed.

   Source: Handbook p. 23

   “There is an easy way to tell if you are following too closely. It is called the “three-second rule,” and it works at any speed.”
   New Mexico Driver Manual, Handbook p. 23

2. You may need a 4 second following distance on slippery roads and when following motorcycles, among other situations.

   Source: Handbook p. 24

   “For example, you may need a four second following distance to be safe; (1) on slippery roads, (2) when following motorcycles,”
   New Mexico Driver Manual, Handbook p. 24

3. To merge or change lanes you need a gap of about 4 seconds.

   Source: Handbook p. 24

   “You need a four-second gap whenever you change lanes, enter a roadway or when your lane merges with another travel lane.”
   New Mexico Driver Manual, Handbook p. 24

4. At 55 mph you need about 10 seconds to pass, so you need a 10 second gap in oncoming traffic.

   Source: Handbook p. 25

   “At a speed of 55 mph, you need about 10 seconds to pass. That means you need a 10 second gap in oncoming traffic and sight-distance to pass.”
   New Mexico Driver Manual, Handbook p. 25

5. Do not start to pass within one third of a mile of a hill or curve.

   Source: Handbook p. 25

   “This means you should not start to pass if you are within one-third of a mile of a hill or curve.”
   New Mexico Driver Manual, Handbook p. 25

6. It is safe to return to your lane when you see both headlights of the passed vehicle in your mirror.

   Source: Handbook p. 25

   “When you can see both headlights of the vehicle you just passed in your rear-view mirror, it is safe to return to the driving lane.”
   New Mexico Driver Manual, Handbook p. 25

7. When passing a bicyclist, try to leave at least 5 feet.

   Source: Handbook p. 25

   “Keep a safe distance when passing a bicyclist, trying for at least five feet, and passing them only when safe and legal to do so.”
   New Mexico Driver Manual, Handbook p. 25

8. A car at 55 mph stops in about 400 feet, but a large truck could take almost 800 feet.

   Source: Handbook p. 27

   “An average car going 55 mph can stop in about 400 feet. But a large truck could take almost 800 feet to stop.”
   New Mexico Driver Manual, Handbook p. 27

9. If you cannot see the truck driver in the side mirror, the driver cannot see you.

   Source: Handbook p. 27

   “In general, if you can't see the driver in the side mirror, the driver can't see you.”
   New Mexico Driver Manual, Handbook p. 27

Numbers to know

3 questions from the New Mexico practice test

1. 1. What following-distance method does the manual say works at any speed?

   1. A fixed one-car-length rule
   2. The three-second rule
   3. The ten-minute mirror rule
   4. Matching the speedometer number in feet
   Show answer

   The three-second rule. The manual uses the three-second rule to judge space behind the vehicle ahead at any speed. Watch the lead vehicle pass a fixed object, count the seconds until your vehicle reaches it, and drop back if you arrive before finishing the count. A fixed car length changes meaning as speed changes, and the mirror and speedometer formulas are not the method described. Increase the time gap beyond three seconds when conditions such as slippery roads, a trailer, or a railroad crossing call for more room.

2. 2. According to the three-second rule, what should you do if you pass the marker before finishing the count?

   1. Drop back and count again at another spot
   2. Keep the same gap because the rule is only for highways
   3. Brake hard immediately at the marker
   4. Change lanes without checking traffic
   Show answer

   Drop back and count again at another spot. Passing the marker before the count ends means the following gap is too short. The manual directs the driver to drop back and count again at another stationary point, repeating the process until the gap is at least three seconds. Keeping the same distance ignores the test, and hard braking at the marker can create a rear-end conflict. A lane change is unrelated unless traffic conditions separately call for it. Use a sign or pole as the reference, count steadily, and build the space before the vehicle ahead needs to brake.

3. 3. An average car at 55 mph can stop in about 400 feet. About how far could a large truck take to stop at the same speed?

   1. About 200 feet
   2. About 400 feet, the same as a car
   3. Almost 800 feet
   4. About 1,500 feet
   Show answer

   Almost 800 feet. The manual says a large truck could take almost 800 feet to stop from 55 mph, about twice the car's 400 feet. Two hundred feet is less than a car needs, and saying the truck stops in the same 400 feet ignores that big rigs take longer to stop. Fifteen hundred feet is not the manual's figure. This is why you should never pull in front of a big rig and then slow down or stop suddenly.

Source: the New Mexico Driver Manual, 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.