1

Need for Speed?

Vehicle speed is an important factor of roadway safety. 

Students will explore how speed is related to the design 

of a street and learn that travel speed is a decision 

made by drivers. Students will discover how a driver’s 

ability to stop is related to human biology and principles 

of physics and how this translates into the distance 

needed for a driver to see a pedestrian and stop. 

Students will learn about these concepts by measuring their own reaction time then 

calculating laying out stopping distances given different conditions.

Supplies

▸ Computer projection

▸ Masking tape

▸ Calculators (1 per student pair)

▸ Standard 12-inch rulers (1 per student pair)

▸ Measuring tape x 4

▸ Scrap paper to record reaction time trials

▸ Optional: clipboards

Supplemental Materials Provided

▸ Visual aid: PowerPoint file with 11 images of

street scenes with different speed limits

(8 labeled and 3 unlabeled for guessing).

▸ Handout: 4 handouts of sample local

news stories.

▸ Handout: Science World reaction timer template

(3 per sheet).

▸ Handout: 12 handouts with sight stopping

distance activity.

Audience: 

Middle school-age 

students

Format:

60-75-minute activity

in a classroom setting

To Do in Advance

 Identify long/wide hallway or outdoor

space (at least 450 feet in length). If you

have less than 400 feet available, do not

offer the last 3 sight stopping distance 

handouts for the 50 mi/hr scenario.

 Print handouts.

 Test computer projection.

 Load PowerPoint.

 Open browser window with online street

imagery of meeting place 

(e.g., Google Streetview).

 Review “The Why and How Behind the

Concepts” in the Primer.

STEM Lessons for Pedestrian Safety: Need for Speed?

FHWA-SA-20-089
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Introduction to Concept 

and Activity

These concepts should be reinforced by 

the lesson leader the during activities.

▸ The faster someone is driving when a crash

occurs, the more severe the impacts. People

outside of vehicles are disproportionately

injured over those protected inside the vehicle.

Street designs that lead to even a small speed

reduction can result in fewer and less severe

crashes.

▸ The design of the street signals to drivers how

fast (or slow) they should be driving. The design

of streets can be changed to encourage

people to drive slower. Slower drivers need less

time than faster drivers to see and react to a

person crossing the street.

Greetings and Icebreaker (5 minutes)

Activity Part 1 (15 minutes): 

Introduce the relationship between street 

type and driving speed by expanding 

upon the Introduction to Concept.

Sample discussion: 

The speed limit tells drivers the maximum speed 

they are allowed to drive on a given road, but 

there are also cues in the design of the road 

and the surrounding environment that make it 

feel more or less comfortable for drivers to drive 

fast. Imagine that I ask you to run on a balance 

beam. How different would it then feel if I asked 

you to run on a path that had grass on each 

side? What about if that path now has buildings 

and other people walking on either side of you? 

Think about the times when you have ridden in 

a car. Do you think the driver is always traveling 

at or below the speed limit? When do you think 

they might choose to drive over the speed limit?

Show the browser window with the street-view of 

an adjacent street. Ask students what they see that 

might encourage a driver to travel faster? What 

would make drivers slow down?

Use visual aid with street images showing speed 

limits. Ask students what clues these scenes offer 

for how fast the drivers might be driving. Next, 

show the last three images while asking students 

to guess the speed and describe their reasoning. 

Activity Part 2 (15 

minutes): Next each student 

will spend a few minutes 

reading a news story about a 

traffic crash in which a person 

walking was injured or killed. 

Ask students to consider what was (or was not) 

mentioned about the factors involved in the crash 

(i.e., where, when, who) and more specifically, 

how the topic of speed was mentioned. Ask a few 

students to share their observations and then help 

synthesize key points for the group.

Key message: Speed is always a factor. Each 

street has a maximum speed limit that can be 

enforced by police/sheriffs/troopers, but it is 

still up to the person driving to decide how fast 

they should be driving given conditions such as 

weather, lighting, and the presence (or expected 

presence) of other vehicles, pedestrians, and 

bicyclists.

Optional: If your students would like an 

additional reading about the way news outlets 

cover traffic crashes, specifically crashes 

involving pedestrians and bicyclists, check out 

the academic article “Does news coverage of 

traffic crashes affect perceived blame and 

preferred solutions? Evidence from an 

experiment.” from the Transportation Research 

Interdisciplinary Perspectives. Available at: 

https://doi.org/10.1016/j.trip.2019.100073

Activity Part 3 (5 minutes):

Introduce the concept of reaction time. 

Sample discussion: 

There are two components in the 

ability of a driver to bring their vehicle 

to a stop once they see a person walking across 

the road (or some other event or object that 

requires stopping). 

First, the driver must perceive the need to stop. 

The vehicle is still traveling during the time it takes 

STEM Lessons for Pedestrian Safety: Need for Speed?
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the driver’s brain react (i.e., the eye sends a 

message to the visual cortex in the brain, which 

perceives that an event is taking place. The visual 

cortex sends a message to the motor cortex to 

initiate the foot pressing the brake pedal). 

Second, the vehicle must physically come to a 

complete stop. This is dependent upon many 

variables including the speed at which the 

vehicle is traveling, the mass of the vehicle, 

the condition of the vehicle (i.e., quality of the 

tires, brakes, gears, etc.), the condition of the 

pavement, and even the acceleration of gravity. 

Next, students will measure their reaction time and 

use those data to calculate the stopping distance 

for different conditions and speeds.

Optional: To offer more information on the 

science behind reaction time, check out the 

“Reaction Time Ruler” activity from Science 

World, available: https://www.scienceworld.ca/

resource/reaction-time-ruler/ 

Activity Part 4 (10 minutes): Ask 

students to pick a partner for the ruler 

drop reaction time test. Distribute a 

reaction timer to each pair. Remind 

students: “this activity is not simply 

measuring your reflex; it is measuring 

the response time to something that you see.” 

Directions:

▸ Each student in the pair needs to complete six

trials of the drop test – three with their right hand

and three with their left hand.

▸ Record the time on the drop timer for each trial.

Each pair should have 12 trials. When complete,

each person should calculate and record their

average drop time.

▸ Catcher rests their arm on the edge of a table

or desk and spreads their thumb and index

finger about 4 centimeters apart.

▸ Dropper holds the ruler near the highest number

and positions the 0 so that it is level within the

top of the catcher’s open fingers.

▸ Dropper releases the ruler within five seconds

and the catcher tries to pinch the ruler as fast as 

possible and then does not move their fingers.

▸ Catcher records the nearest time notch in

seconds.

▸ Repeat five more times and then switch roles.

The dropper should always vary the time of

dropping within the five-second “drop-zone.” 

If time allows, ask: What trends did you notice in 

your reaction times across the trials? What factors 

might affect someone’s reaction time, in general? 

What factors might increase the reaction time 

specifically of drivers? For context, mention that 

2 or 2.5 seconds are often used as the “standard” 

reaction time in the field of road design and 

transportation safety. How does that compare to 

what you observed today?

Optional: The distance the reaction timer 

travels before it is caught has been converted 

to time using the equation d = 1/2at2 where a is 

acceleration due to gravity. Rather than giving 

the students the conversion, you could ask them 

to solve for time using the distance on the ruler. 

Activity Part 5 (10 minutes):

Distribute a stopping distance 

calculation handout to each student 

and tell them that each sheet is 

different, but it includes the directions 

they need to complete the activity. Below is the 

equation students will see on their handout:

Stopping Sight Distance (SSD)*

SSD = vt + (v2/30[a/g])

v = velocity when brakes are applied (given on 

the handout. Students will convert from mi/hr 

to ft/s by multiplying by 1.47)

t = time to perceive the need to stop (student’s 

reaction time measured in seconds)

a = driver deceleration of the vehicle (given on 

the handout)

g = acceleration of gravity (first, ask students if 

anyone knows this number. Answer: 32.2 ft/s2)

*This equation assumes a road without grade. The

next part has an optional activity where students

can explore how grade effects SSD.

STEM Lessons for Pedestrian Safety: Need for Speed?
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Activity Part 6 (15 minutes): Ask 

students to gather their handouts and 

writing implements and move to the 

designated hallway or outdoor space. 

Mark a starting spot for each speed (20, 30, 

40, and 50 mi/hr). Students will take turns 

using the measuring tape and masking tape to 

measure and mark the stopping distance for their 

given conditions and write their name or initials 

on the tape. Ask students to compare results 

amongst themselves or ask everyone with the 

same speed to gather at their marking and report 

the deceleration assumption included in their 

calculation. If more than one student had the 

same handout, ask about their reaction time so 

students can observe the difference. 

Ask a few questions to wrap-up: What do you 

think will happen to these calculations if a driver 

is traveling uphill? Downhill? What happens when 

drivers are traveling above the posted speed 

limit (recall the images from the beginning of the 

lesson and the differences between the speeds 

shown on the floor, i.e., 30 mi/hr+ on a street that 

should be maximum 20 mi/hr)? What about in 

different weather conditions? Light conditions? If 

the driver is tired or impaired by drugs or alcohol? 

Many of these reasons are why the fields of 

road design and transportation safety assume a 

reaction time of 2 or 2.5 seconds.

Optional: Bring clipboards to the designated 

space. Present students with the revised equation 

that incorporates grade. Randomly assign 

students to incorporate a -6%, -3%, 3%, or 6% 

grade into their calculation. 

SSD = vt + (v2/2g[30 + G])

G = grade of the road (for example, for a 3% 

uphill add 0.03 to the acceleration of gravity).

Ask for volunteers to add or subtract distance 

from their original measurement on the ground.

Optional: Ask students to model the grade using 

materials available in the classroom. This will help 

them visualize the changes associated with their 

new calculations.

Notes

STEM Lessons for Pedestrian Safety: Need for Speed?
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NEWS

Student Handout: Activity 2 - News Story 1

Driver hits, kills pedestrian on east side as 

pedestrian deaths continue to increase city-wide

Police are investigating a fatal crash on the east 

side Saturday evening. Shortly before 7 p.m., 

police were called to the 2500 block of North 

Main Street on a report of driver striking 

a pedestrian. Police say a 46-year-old man was attempting to cross Main Street between a bus stop 

and the Walgreens when the driver struck him with 

his car. The injured pedestrian was unresponsive 

at the scene and reportedly died on the way to the 

hospital. Police say the driver was not impaired and 

remained at the scene.

This is the eighth death of a pedestrian in the city 

this year, an increase of 20% from last year at this 

time. Three pedestrians have died on this stretch of 

Main Street, which, despite being a busy shopping 

area, has high traffic speeds and a lack of streetlights. 

Source: https://www.sciencedirect.com/science/article/pii/S2590198219300727#bbb0005

Write your 

observations 

here

STEM Lessons for Pedestrian Safety: Need for Speed?
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NEWS

Student Handout: Activity 2 - News Story 2

Pedestrian dies after being struck on 

Highway 205 in Marion Valley

MARION VALLEY — A Raeford City woman died Thursday night 

after being struck by a driver while she was attempting to cross 

Highway 205 on foot. 

According to reports from the Department of Public Safety, Maria 

Elena Jacinto, 33, was pronounced dead at Amity Regional Hospital 

in Northfork.

The accident took place around 9:41 p.m. in the 

vicinity of Highway 205 Pinegrove Drive in Marion Valley. 

Reports indicate that a Jeep SUV struck Jacinto. The driver told 

troopers he had just crossed the state line while returning from 

a conference, traveling south on Highway 205, when Jacinto 

appeared in front of him on the roadway. He said he could not stop in 

time to avoid the accident.

The name of the driver has not been released. The accident is 

under investigation by the Department of Public Safety. The Marion 

County Sheriff ’s Office assisted at the scene.

Write your 

observations 

here

STEM Lessons for Pedestrian Safety: Need for Speed?
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NEWS

Student Handout: Activity 2 - News Story 3

Woman struck by vehicle on Franklin Avenue 

succumbs to her injuries Tuesday evening

GREENVILLE — A pedestrian who was struck by a vehicle while crossing a poorly lit area on Franklin 

Avenue Monday night succumbed to her injuries after being transported to a local hospital. 

Police report the crash occurred on Franklin Avenue between Lassen Drive and Interstate 75 at about 8:15 

p.m. when a 42-year-old woman walking south across Franklin Avenue was struck by a 2009 Ford truck

driven by an 18-year-old man who was traveling east on Franklin.

The woman was attempting to cross the road in the middle of the block and was not using a marked 

crosswalk, police say. 

The driver of the pickup truck remained on scene following the crash and was cooperative with police.

Alcohol or excessive speed are not considered to be contributing factors in the crash. The incident is still 

under investigation by Greenville police but, at this 

time, no charges are expected in this case.

Greenville police, fire and ambulance responded to 

the scene. The woman was transported to Greenville 

Regional Medical Center where she was pronounced 

dead shortly after arrival.

The name of the victim will be released once her 

family has been notified, police said.

Write your 

observations 

here

STEM Lessons for Pedestrian Safety: Need for Speed?
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LANGSTON — A crash involving a pedestrian has 

closed Williams Highway at Lebanon Pass Road, 

according to Langston police.

A woman was in a crosswalk when she was hit 

by a man in an SUV turning right onto Williams 

Highway. The driver administered first aid until 

police and the Rock County Emergency Medical 

Services arrived at the scene. The pedestrian suffered 

serious injuries and was taken to a hospital.

Speed and alcohol are not factors, police said. The 

police did not comment on whether they thought 

driver distraction was a factor, but they mentioned 

that the pedestrian was wearing dark clothing. The 

incident remains under investigation.

A detour has been established on Turner Avenue 

from 50th to 125th. Police ask that you avoid the 

area.

NEWS

Student Handout: Activity 2 - News Story 4

Pedestrian injured by SUV driver on Williams 

Highway at Lebanon Pass Road

Write your 

observations 

here

STEM Lessons for Pedestrian Safety: Need for Speed?
Student Handout: Activity 4 - Reaction Timer 

https://www.scienceworld.ca/resource/reaction-time-ruler/

STEM Lessons for Pedestrian Safety: Need for Speed?
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Instructor Handout: Activities 5 & 6 - Stopping Sight Distance

Note to Lesson Leader: There are 12 handouts, each with a unique combination of velocity and 

deceleration rate (see key below). If you have more than 12 students, duplicate handouts will allow 

students to see during Activity Part 6 how different reaction times result in different stopping distances 

while holding other variables constant.

Handout Key

Velocity

Deceleration Rate

20 ft/s 11.2 ft/s 2 ft/s

20 mi/hr Handout 1 Handout 2 Handout 3

30 mi/hr Handout 4 Handout 5 Handout 6

40 mi/hr Handout 7 Handout 8 Handout 9

50 mi/hr Handout 10 Handout 11 Handout 12

Sample Solution 

(for parameters on Handout 5)

SSD = vt + (v2/30[a/g]) 

v = 30 mi/hr x 1.47

 = 44.1 ft/s2

t = assume 0.15 seconds

SSD = 44.1 x 0.15 + (44.12 / 30 [11.2/32.2])

 = 6.6 + (1944.8 / 30 [0.35])

 = 6.6 + (1944.8 / 10.4)

 = 6.6 + 187

SSD = 193 feet

STEM Lessons for Pedestrian Safety: Need for Speed?
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Student Handout: Activities 5 & 6 - Stopping Sight Distance 

Handout 1

Now that you have measured your average reaction time, you will use that number to calculate 

stopping sight distance (SSD). 

SSD = vt + (v2/30[a/g])

Your assignment is to calculate SSD for a vehicle traveling 20 miles per hour and with a 

deceleration rate of 20 feet per second using the equation above. 

Key:

v = velocity (definition: the speed and direction of motion of an object). In your case, this will 

be the velocity the vehicle is traveling when the brakes are applied. Convert your assigned 

velocity to feet per second by multiplying by a conversion factor of 1.47.

t = time to perceive the need to stop (your average reaction time from the ruler drop test)

a = driver deceleration of the vehicle. Deceleration is a complex variable that depends on 

factors such as the weight to power ratio of the vehicle, pavement conditions, and the 

urgency with which the driver applies the brakes. 20 feet per second would be an urgent 

stop in a standard passenger vehicle (example: 4-door car, minivan, small pick-up truck) 

that is so abrupt that it may not be comfortable for passengers. Regardless of the velocity, 

this means that your driver is decelerating the vehicle 20 feet per second for each second

that passes until the vehicle comes to a stop.

g = acceleration of gravity, 32.2 ft/s2

STEM Lessons for Pedestrian Safety: Need for Speed?
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Student Handout: Activities 5 & 6 - Stopping Sight Distance 

Handout 2

Now that you have measured your average reaction time, you will use that number to calculate 

stopping sight distance (SSD). 

SSD = vt + (v2/30[a/g])

Your assignment is to calculate SSD for a vehicle traveling 20 miles per hour and with a 

deceleration rate of 11.2 feet per second using the equation above. 

Key:

v = velocity (definition: the speed and direction of motion of an object). In your case, this will 

be the velocity the vehicle is traveling when the brakes are applied. Convert your assigned 

velocity to feet per second by multiplying by a conversion factor of 1.47.

t = time to perceive the need to stop (your average reaction time from the ruler drop test)

a = driver deceleration of the vehicle. Deceleration is a complex variable that depends on 

factors such as the weight to power ratio of the vehicle, pavement conditions, and the 

urgency with which the driver applies the brakes. 11.2 feet per second would be braking 

action in a standard passenger vehicle (example: 4-door car, minivan, small pickup truck) that is comfortable for the driver and passengers even on wet pavement. 

Regardless of the velocity, this means that your driver is decelerating the vehicle 

11.2 feet per second for each second that passes until the vehicle comes to a stop.

g = acceleration of gravity, 32.2 ft/s2

STEM Lessons for Pedestrian Safety: Need for Speed?
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Student Handout: Activities 5 & 6 - Stopping Sight Distance 

Handout 3

Now that you have measured your average reaction time, you will use that number to calculate 

stopping sight distance (SSD). 

SSD = vt + (v2/30[a/g])

Your assignment is to calculate SSD for a vehicle traveling 20 miles per hour and with a 

deceleration rate of 2 feet per second using the equation above. 

Key:

v = velocity (definition: the speed and direction of motion of an object). In your case, this will 

be the velocity the vehicle is traveling when the brakes are applied. Convert your assigned 

velocity to feet per second by multiplying by a conversion factor of 1.47.

t = time to perceive the need to stop (your average reaction time from the ruler drop test)

a = driver deceleration of the vehicle. Deceleration is a complex variable that depends on 

factors such as the weight to power ratio of the vehicle, pavement conditions, and the 

urgency with which the driver applies the brakes. 2 feet per second would be braking 

action in a truck that is comfortable for the driver and passengers on dry pavement.

Regardless of the velocity, this means that your driver is decelerating the vehicle 2 feet per 

second for each second that passes until the vehicle comes to a stop.

g = acceleration of gravity, 32.2 ft/s2

STEM Lessons for Pedestrian Safety: Need for Speed?
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Student Handout: Activities 5 & 6 - Stopping Sight Distance 

Handout 4

Now that you have measured your average reaction time, you will use that number to calculate 

stopping sight distance (SSD). 

SSD = vt + (v2/30[a/g])

Your assignment is to calculate SSD for a vehicle traveling 30 miles per hour and with a 

deceleration rate of 20 feet per second using the equation above. 

Key:

v = velocity (definition: the speed and direction of motion of an object). In your case, this will 

be the velocity the vehicle is traveling when the brakes are applied. Convert your assigned 

velocity to feet per second by multiplying by a conversion factor of 1.47.

t = time to perceive the need to stop (your average reaction time from the ruler drop test)

a = driver deceleration of the vehicle. Deceleration is a complex variable that depends on 

factors such as the weight to power ratio of the vehicle, pavement conditions, and the 

urgency with which the driver applies the brakes. 20 feet per second would be an urgent 

stop in a standard passenger vehicle (example: 4-door car, minivan, small pick-up truck) 

that is so abrupt that it may not be comfortable for passengers. Regardless of the velocity, 

this means that your driver is decelerating the vehicle 20 feet per second for each second 

that passes until the vehicle comes to a stop.

g = acceleration of gravity, 32.2 ft/s2

STEM Lessons for Pedestrian Safety: Need for Speed?
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Student Handout: Activities 5 & 6 - Stopping Sight Distance 

Handout 5

Now that you have measured your average reaction time, you will use that number to calculate 

stopping sight distance (SSD). 

SSD = vt + (v2/30[a/g])

Your assignment is to calculate SSD for a vehicle traveling 30 miles per hour and with a 

deceleration rate of 11.2 feet per second using the equation above. 

Key:

v = velocity (definition: the speed and direction of motion of an object). In your case, this will 

be the velocity the vehicle is traveling when the brakes are applied. Convert your assigned 

velocity to feet per second by multiplying by a conversion factor of 1.47.

t = time to perceive the need to stop (your average reaction time from the ruler drop test)

a = driver deceleration of the vehicle. Deceleration is a complex variable that depends on 

factors such as the weight to power ratio of the vehicle, pavement conditions, and the 

urgency with which the driver applies the brakes. 11.2 feet per second would be braking 

action in a standard passenger vehicle (example: 4-door car, minivan, small pickup truck) that is comfortable for the driver and passengers even on wet pavement. 

Regardless of the velocity, this means that your driver is decelerating the vehicle 11.2 feet per 

second for each second that passes until the vehicle comes to a stop.

g = acceleration of gravity, 32.2 ft/s2

STEM Lessons for Pedestrian Safety: Need for Speed?
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Student Handout: Activities 5 & 6 - Stopping Sight Distance 

Handout 6

Now that you have measured your average reaction time, you will use that number to calculate 

stopping sight distance (SSD). 

SSD = vt + (v2/30[a/g])

Your assignment is to calculate SSD for a vehicle traveling 30 miles per hour and with a 

deceleration rate of 2 feet per second using the equation above. 

Key:

v = velocity (definition: the speed and direction of motion of an object). In your case, this will 

be the velocity the vehicle is traveling when the brakes are applied. Convert your assigned 

velocity to feet per second by multiplying by a conversion factor of 1.47.

t = time to perceive the need to stop (your average reaction time from the ruler drop test)

a = driver deceleration of the vehicle. Deceleration is a complex variable that depends on 

factors such as the weight to power ratio of the vehicle, pavement conditions, and the 

urgency with which the driver applies the brakes. 2 feet per second would be braking 

action in a truck that is comfortable for the driver and passengers on dry pavement. 

Regardless of the velocity, this means that your driver is decelerating the vehicle 2 feet per 

second for each second that passes until the vehicle comes to a stop.

g = acceleration of gravity, 32.2 ft/s2

STEM Lessons for Pedestrian Safety: Need for Speed?
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Student Handout: Activities 5 & 6 - Stopping Sight Distance 

Handout 7

Now that you have measured your average reaction time, you will use that number to calculate 

stopping sight distance (SSD). 

SSD = vt + (v2/30[a/g])

Your assignment is to calculate SSD for a vehicle traveling 40 miles per hour and with a 

deceleration rate of 20 feet per second using the equation above. 

Key:

v = velocity (definition: the speed and direction of motion of an object). In your case, this will 

be the velocity the vehicle is traveling when the brakes are applied. Convert your assigned 

velocity to feet per second by multiplying by a conversion factor of 1.47.

t = time to perceive the need to stop (your average reaction time from the ruler drop test)

a = driver deceleration of the vehicle. Deceleration is a complex variable that depends on 

factors such as the weight to power ratio of the vehicle, pavement conditions, and the 

urgency with which the driver applies the brakes. 20 feet per second would be an urgent 

stop in a standard passenger vehicle (example: 4-door car, minivan, small pick-up truck) 

that is so abrupt that it may not be comfortable for passengers. Regardless of the velocity, 

this means that your driver is decelerating the vehicle 20 feet per second for each second 

that passes until the vehicle comes to a stop.

g = acceleration of gravity, 32.2 ft/s2

STEM Lessons for Pedestrian Safety: Need for Speed?
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Student Handout: Activities 5 & 6 - Stopping Sight Distance 

Handout 8

Now that you have measured your average reaction time, you will use that number to calculate 

stopping sight distance (SSD). 

SSD = vt + (v2/30[a/g])

Your assignment is to calculate SSD for a vehicle traveling 40 miles per hour and with a 

deceleration rate of 11.2 feet per second using the equation above. 

Key:

v = velocity (definition: the speed and direction of motion of an object). In your case, this will 

be the velocity the vehicle is traveling when the brakes are applied. Convert your assigned 

velocity to feet per second by multiplying by a conversion factor of 1.47.

t = time to perceive the need to stop (your average reaction time from the ruler drop test)

a = driver deceleration of the vehicle. Deceleration is a complex variable that depends on 

factors such as the weight to power ratio of the vehicle, pavement conditions, and the 

urgency with which the driver applies the brakes. 11.2 feet per second would be braking 

action in a standard passenger vehicle (example: 4-door car, minivan, small pickup truck) that is comfortable for the driver and passengers even on wet pavement. 

Regardless of the velocity, this means that your driver is decelerating the vehicle 11.2 feet per 

second for each second that passes until the vehicle comes to a stop.

g = acceleration of gravity, 32.2 ft/s2

STEM Lessons for Pedestrian Safety: Need for Speed?
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Student Handout: Activities 5 & 6 - Stopping Sight Distance 

Handout 9

Now that you have measured your average reaction time, you will use that number to calculate 

stopping sight distance (SSD). 

SSD = vt + (v2/30[a/g])

Your assignment is to calculate SSD for a vehicle traveling 40 miles per hour and with a 

deceleration rate of 2 feet per second using the equation above. 

Key:

v = velocity (definition: the speed and direction of motion of an object). In your case, this will 

be the velocity the vehicle is traveling when the brakes are applied. Convert your assigned 

velocity to feet per second by multiplying by a conversion factor of 1.47.

t = time to perceive the need to stop (your average reaction time from the ruler drop test)

a = driver deceleration of the vehicle. Deceleration is a complex variable that depends on 

factors such as the weight to power ratio of the vehicle, pavement conditions, and the 

urgency with which the driver applies the brakes. 2 feet per second would be braking 

action in a truck that is comfortable for the driver and passengers on dry pavement. 

Regardless of the velocity, this means that your driver is decelerating the vehicle 2 feet per 

second for each second that passes until the vehicle comes to a stop.

g = acceleration of gravity, 32.2 ft/s2

STEM Lessons for Pedestrian Safety: Need for Speed?
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Student Handout: Activities 5 & 6 - Stopping Sight Distance 

Handout 10

Now that you have measured your average reaction time, you will use that number to calculate 

stopping sight distance (SSD). 

SSD = vt + (v2/30[a/g])

Your assignment is to calculate SSD for a vehicle traveling 50 miles per hour and with a 

deceleration rate of 20 feet per second using the equation above. 

Key:

v = velocity (definition: the speed and direction of motion of an object). In your case, this will 

be the velocity the vehicle is traveling when the brakes are applied. Convert your assigned 

velocity to feet per second by multiplying by a conversion factor of 1.47.

t = time to perceive the need to stop (your average reaction time from the ruler drop test)

a = driver deceleration of the vehicle. Deceleration is a complex variable that depends on 

factors such as the weight to power ratio of the vehicle, pavement conditions, and the 

urgency with which the driver applies the brakes. 20 feet per second would be an urgent 

stop in a standard passenger vehicle (example: 4-door car, minivan, small pick-up truck) 

that is so abrupt that it may not be comfortable for passengers. Regardless of the velocity, 

this means that your driver is decelerating the vehicle 20 feet per second for each second

that passes until the vehicle comes to a stop.

g = acceleration of gravity, 32.2 ft/s2

STEM Lessons for Pedestrian Safety: Need for Speed?
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Student Handout: Activities 5 & 6 - Stopping Sight Distance 

Handout 11

Now that you have measured your average reaction time, you will use that number to calculate 

stopping sight distance (SSD). 

SSD = vt + (v2/30[a/g])

Your assignment is to calculate SSD for a vehicle traveling 50 miles per hour and with a 

deceleration rate of 11.2 feet per second using the equation above. 

Key:

v = velocity (definition: the speed and direction of motion of an object). In your case, this will 

be the velocity the vehicle is traveling when the brakes are applied. Convert your assigned 

velocity to feet per second by multiplying by a conversion factor of 1.47.

t = time to perceive the need to stop (your average reaction time from the ruler drop test)

a = driver deceleration of the vehicle. Deceleration is a complex variable that depends on 

factors such as the weight to power ratio of the vehicle, pavement conditions, and the 

urgency with which the driver applies the brakes. 11.2 feet per second would be braking 

action in a standard passenger vehicle (example: 4-door car, minivan, small pickup truck) that is comfortable for the driver and passengers even on wet pavement.

Regardless of the velocity, this means that your driver is decelerating the vehicle 11.2 feet per 

second for each second that passes until the vehicle comes to a stop.

g = acceleration of gravity, 32.2 ft/s2

STEM Lessons for Pedestrian Safety: Need for Speed?
22

Student Handout: Activities 5 & 6 - Stopping Sight Distance 

Handout 12

Now that you have measured your average reaction time, you will use that number to calculate 

stopping sight distance (SSD). 

SSD = vt + (v2/30[a/g])

Your assignment is to calculate SSD for a vehicle traveling 50 miles per hour and with a 

deceleration rate of 2 feet per second using the equation above. 

Key:

v = velocity (definition: the speed and direction of motion of an object). In your case, this will 

be the velocity the vehicle is traveling when the brakes are applied. Convert your assigned 

velocity to feet per second by multiplying by a conversion factor of 1.47.

t = time to perceive the need to stop (your average reaction time from the ruler drop test)

a = driver deceleration of the vehicle. Deceleration is a complex variable that depends on 

factors such as the weight to power ratio of the vehicle, pavement conditions, and the 

urgency with which the driver applies the brakes. 2 feet per second would be braking 

action in a truck that is comfortable for the driver and passengers on dry pavement. 

Regardless of the velocity, this means that your driver is decelerating the vehicle 2 feet per 

second for each second that passes until the vehicle comes to a stop.

g = acceleration of gravity, 32.2 ft/s2

STEM Lessons for Pedestrian Safety: Need for Speed?