Key points
The Three Second Rule is an easy way to tell if you are following too closely, and it works at any speed.
Source: Handbook p. 64
“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.”
Montana Driver Manual, Handbook p. 64You are following too closely if you reach the mark before you finish counting.
Source: Handbook p. 64
“You are following too closely if you pass the mark before you finish counting.”
Montana Driver Manual, Handbook p. 64In some situations, such as on slippery roads, you may need a four second following distance.
Source: Handbook p. 65
“In these situations, you may need a foursecond following distance to be safe. ■ On slippery roads - As you need more distance to stop your vehicle on slippery roads, you must leave more space in front of you.”
Montana Driver Manual, Handbook p. 65If you are being tailgated and there is a right lane, move over to the right.
Source: Handbook p. 65
“If you are being followed too closely and there is a right lane, move over to the right.”
Montana Driver Manual, Handbook p. 65You need a gap of about four seconds anytime you want to merge with other traffic.
Source: Handbook p. 66
“You need a gap of about four seconds anytime you want to merge with other traffic.”
Montana Driver Manual, Handbook p. 66At 55 mph you need over 1600 feet, about one third of a mile, to pass safely.
Source: Handbook p. 67
“At 55 mph you will travel over 800 feet in 10 seconds. So will an oncoming vehicle. That means you need over 1600 feet or about one-third of a mile to pass safely.”
Montana Driver Manual, Handbook p. 67Do not start to pass within one third of a mile of a hill or curve.
Source: Handbook p. 67
“This means you should not start to pass if you are within one-third of a mile of a hill or a curve.”
Montana Driver Manual, Handbook p. 67It is safe to return to your lane when you can see both headlights of the passed vehicle in your rearview mirror.
Source: Handbook p. 67
“When you can see both headlights of the vehicle you just passed in your rearview mirror, it is safe to return to the driving lane.”
Montana Driver Manual, Handbook p. 67When splitting the difference between two hazards, leave a little more room on the more dangerous side, such as the side an oncoming tractor trailer will pass.
Source: Handbook p. 66
“However, if one is more dangerous than the other, leave a little more space on the danger side. For example, if the oncoming vehicle is a tractor-trailer, leave a little more room on the side that the truck will pass.”
Montana Driver Manual, Handbook p. 66It is illegal to sound your horn when approaching or passing a horse.
Source: Handbook p. 68
“It is illegal to sound your horn when approaching or passing a horse.”
Montana Driver Manual, Handbook p. 68
Numbers to know
| Number | What it means | Manual |
|---|---|---|
| 3 seconds | follow no closer than this behind the vehicle ahead | Handbook p. 64 |
| 4 seconds | gap needed to merge with other traffic | Handbook p. 66 |
| 10 seconds | time needed to pass at 55 mph | Handbook p. 66 |
| 1600 feet | clear road needed to pass, about one third of a mile | Handbook p. 67 |
| 55 mph | the speed these passing figures assume | Handbook p. 67 |
3 questions from the Montana practice test
1. What following interval does Montana's Three-Second Rule use at any speed?
- Ten seconds only on interstate highways
- Exactly one second behind the vehicle ahead
- A distance of three vehicle lengths
- At least three seconds between reaching the same fixed point
Show answer
At least three seconds between reaching the same fixed point. The Three-Second Rule is a time-based check that works at any speed. Watch the vehicle ahead pass a fixed object, count one-one-thousand through three-one-thousand, and make sure your vehicle does not reach that object before the count ends. One second leaves too little reaction and braking time. Vehicle lengths change with car size and speed, so they are not the manual's measure. Ten seconds is associated with passing at 55 mph, not ordinary following. Pick a sign or pole and count rather than guessing by appearance.
2. How much clear road does the Montana manual say you need to pass safely?
- About 200 feet
- Over 1,600 feet, about one third of a mile
- About 400 feet
- About five miles
Show answer
Over 1,600 feet, about one third of a mile. At 55 mph you travel over 800 feet in the roughly 10 seconds a pass takes, and so does an oncoming vehicle. That means you need over 1,600 feet, about one third of a mile, of clear road to pass safely. It is hard to judge the speed of oncoming vehicles at that distance, so if you are not sure, wait. You should also not start to pass within one third of a mile of a hill or a curve, because your view of oncoming traffic is blocked.
3. Under Montana's Split the Difference Rule, how should you position your vehicle when passing between parked cars and an oncoming tractor-trailer?
- Leave a little more room on the side that the truck will pass
- Move closer to the truck to stay away from the parked cars
- Drive on the shoulder until the truck is gone
- Keep exactly equal distance from both hazards
Show answer
Leave a little more room on the side that the truck will pass. Montana's Split the Difference Rule says to steer a middle course between two hazards, such as oncoming and parked vehicles. However, if one is more dangerous than the other, leave a little more space on the danger side. The manual's own example is an oncoming tractor-trailer: leave a little more room on the side that the truck will pass. Moving toward the truck reduces that cushion, the shoulder is not a travel path, and rigidly equal spacing ignores the greater danger.
Practice this topic
Lock it in with safe driving questions from the free Montana practice test. Every answer comes with a plain English explanation.
Source: the Montana Driver Manual, Chapter 5: How to Drive Safely. 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.