roadwise.Open study app

Alaska driving lesson · Speed, Following Distance & Highways

Speed, impact & stopping distance

A 3-minute lesson from the Alaska course. Read the rules and examples, follow the handbook page references, and check your understanding before you move on.

Study this lesson in the app Back to the course
Read time
3 minutes
Course unit
Speed, Following Distance & Highways
Checkpoint questions
6
Source pages
33, 34, 68, 86

Speed doesn't add danger in a straight line. Double your speed and the impact and braking distance don't double; they quadruple. Respect that power every time you speed up.

Impact and braking distance compared to 20 mph

Impact and braking distance compared to 20 mph
SpeedImpact and braking distance
40 mph (double)4 times greater
60 mph (triple)9 times greater
80 mph16 times greater
Handbook p. 33 ↗

Know the rule

Both the striking power and the braking distance grow this way. Speed adjusted to traffic, road and weather and managed by a considerate driver need not be dangerous.

Handbook p. 33 ↗

Total stopping distance (handbook chart)

Total stopping distance (handbook chart)
SpeedChart segmentsTotal
20 mph22 ft + 37 ft59 ft
40 mph44 ft + 112 ft156 ft
60 mph66 ft + 226 ft292 ft
Handbook p. 86 ↗
3/4 second

Time it takes to react and step on the brake; at 50 mph you travel another 55 feet in that time

Handbook p. 86 ↗

Know the rule

Once you hit the brakes at 50 mph, you may go another 160 feet or more before you stop.

Handbook p. 86 ↗

Know the rule

A motor-driven cycle's speed is limited by how far its headlamp reveals a person or vehicle.

Handbook p. 34 ↗

Motor-driven cycle headlamp limits

Motor-driven cycle headlamp limits
Headlamp reveals atSpeed allowed
100 feet20 mph or less
200 feet21 to 29 mph
300 feet30 mph or more
Handbook p. 34 ↗

Know the rule

Speed is a direct contributor to crash severity because kinetic energy = 1/2 mass x velocity squared.

Handbook p. 68 ↗

Put it into practice

You usually drive a road at 40 mph but you're running late and do 60. Compared to 20 mph, your braking distance and impact were 4 times greater; now they're 9 times greater.

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.

How much greater is a vehicle's impact and braking distance at 40 mph compared to 20 mph?
  1. 2 times greater
  2. 6 times greater
  3. 4 times greater
  4. 8 times greater

Answer: 4 times greater

Doubling speed from 20 to 40 mph makes impact and braking distance 4 times greater.

Handbook p. 33 ↗
How much greater is a vehicle's impact and braking distance at 60 mph compared to 20 mph?
  1. 3 times greater
  2. 4 times greater
  3. 12 times greater
  4. 9 times greater

Answer: 9 times greater

Tripling speed from 20 to 60 mph makes impact and braking distance 9 times greater.

Handbook p. 33 ↗
How much greater is a vehicle's impact and braking distance at 80 mph compared to 20 mph?
  1. 16 times greater
  2. 9 times greater
  3. 20 times greater
  4. 12 times greater

Answer: 16 times greater

At 80 mph, impact and braking distance are 16 times greater than at 20 mph.

Handbook p. 33 ↗
If a motor-driven cycle's headlamp reveals a person or vehicle at only 100 feet, what is the maximum speed allowed?
  1. 30 mph or less
  2. 20 mph or less
  3. 21 to 29 mph
  4. 40 mph or less

Answer: 20 mph or less

A 100-foot headlamp reveal distance limits motor-driven cycle speed to 20 mph or less.

Handbook p. 34 ↗
If a motor-driven cycle's headlamp reveals a person or vehicle at 300 feet, what speed is allowed?
  1. 20 mph or less
  2. 21 to 29 mph
  3. 30 mph or more
  4. 15 mph or less

Answer: 30 mph or more

A 300-foot reveal distance allows speeds of 30 mph or more.

Handbook p. 34 ↗
Doubling your speed from 20 to 40 mph doubles your vehicle's braking distance.
  1. True
  2. False

Answer: False

Doubling speed from 20 to 40 mph makes braking distance 4 times greater, not just double.

Handbook p. 33 ↗
Take the lesson checkpoint in the app

More in Speed, Following Distance & Highways

All Alaska lessons