Following distance and stopping distance

Most rear-end collisions are caused by following too closely. The space ahead of you is the easiest to control, so keep enough of it to stop if the car ahead does.

Following distance

The space cushion between your vehicle and the one ahead. Base it on traffic speed and road conditions, leaving enough room to stop if necessary.

Handbook p. 38 ↗

Know the rule

The old rule of thumb was one car length for every ten miles per hour. The "two-second rule" is easier to apply and gives a safer distance.

Handbook p. 38 ↗

Using the two-second rule:

Pick a fixed object ahead, such as a sign post, tree, overpass or bridge abutment
When the vehicle ahead passes it, count "one thousand one, one thousand two"
If you reach the object before you finish, you're too close; gradually slow down

Handbook p. 38 ↗

Car-length rule vs. two-second rule

Car-length rule vs. two-second rule
Speed	Feet per second	1 car length/10 mph	2-second rule
30 mph	44.4	60 ft back	88.8 ft back
40 mph	58.6	80 ft back	117.2 ft back
50 mph	73.3	100 ft back	146.6 ft back

Handbook p. 38 ↗

4–5 seconds

Following count when road or weather conditions aren't good, or in vehicles longer than cars

Handbook p. 38 ↗

Know the rule

Watch for brake lights ahead and a shrinking gap. If you see either, move your foot to the brake promptly so you're ready to stop.

Handbook p. 38 ↗

Stopping distance (eye to brain to foot to wheel to road)

Stopping distance (eye to brain to foot to wheel to road)
Speed	Thinking	Braking	Total
25 mph	27 ft	34.7 ft	61.7 ft
35 mph	38 ft	68 ft	106 ft
45 mph	49 ft	112.5 ft	161.5 ft
55 mph	60 ft	168 ft	228 ft
65 mph	71 ft	234.7 ft	305.7 ft

Handbook p. 39 ↗

Actual stopping distance depends on:

Your mental and physical reaction time
Type and condition of the pavement (rough dry concrete vs. slippery brick or smooth asphalt)
Type, condition, size and tread of your tires
Chassis design, weight distribution, suspension and shock absorbers
Type, condition and balance of your brakes
Wind direction and speed, such as a strong tail wind

Handbook p. 38 ↗

Know the rule

Large, wide tires may stop quicker on smooth, dry surfaces but skid or hydroplane more easily when wet. Small, narrow tires may cut through water but lose overall stopping power.

Handbook p. 39 ↗

Put it into practice

It's raining on the interstate. The car ahead passes an overpass and you count "one thousand one…" and pass it yourself. You're far too close: ease off until you have a four- or five-second gap.

Check your understanding

Read the question, decide on an answer, then open it to check the explanation. These are Roadwise study questions based on the source handbook.

What is the “two-second rule” used for?

Measuring how long to signal before a turn
Timing how long a yellow light lasts
Deciding when to merge onto a freeway
Keeping a safe following distance

Answer: Keeping a safe following distance

The two-second rule helps a driver judge a safe following distance behind the vehicle ahead.

Handbook p. 38 ↗

In poor weather or when driving a longer vehicle, how much should you extend the two-second following count?

Four or five seconds
Three seconds
Six to eight seconds
Ten seconds

Answer: Four or five seconds

In bad weather, or when driving longer vehicles, the following distance should increase to a four- or five-second count.

Handbook p. 38 ↗

At 55 mph, what is the total stopping distance (thinking plus braking) listed in the handbook's chart?

106 feet
228 feet
305.7 feet
161.5 feet

Answer: 228 feet

The stopping distance chart lists 228 feet total at 55 mph (60 feet thinking, 168 feet braking).

Handbook p. 39 ↗

Which factor does the handbook NOT list as affecting your vehicle's stopping distance?

The size of the engine
The condition of your brakes
The type and condition of your tires
Wind direction and velocity

Answer: The size of the engine

The handbook lists reaction time, pavement, tires, chassis and suspension, brakes and wind as stopping-distance factors, but not engine size.

Handbook p. 39 ↗

The old rule-of-thumb for following distance was one car length for how many mph of speed?

Every twenty-five miles per hour
Every ten miles per hour
Every fifteen miles per hour
Every five miles per hour

Answer: Every ten miles per hour

Before the two-second rule, the older formula was one car length for every ten miles per hour.

Handbook p. 38 ↗

When road and weather conditions are poor, the handbook says to increase your following distance to a three-second count.

True
False

Answer: False

False. The two-second rule applies in good and bad weather, but in poor road or weather conditions the handbook says to increase following distance to a four or five second count.

Handbook p. 38 ↗