RE:view - Winter 2006
Instructional Strategies for
Teaching Judgment in
Detecting Gaps for
Crossing Streets
With No Traffic Controls
Dona Sauerburger
In this article, I provide instructional strategies for the concepts and skills of crossing
streets that have no stop sign or traffic signal. Such situations include crossing the main
street at intersections with stop signs for the secondary street, at roundabouts or traffic
circles, separate right-turn lanes, and mid-block crosswalks. In these situations, unless
pedestrians rely on drivers to yield, they must cross during a gap in traffic that is long
enough for them to cross, which means (a) such gaps in traffic must exist and (b) the
pedestrians must be able to determine that a gap is long enough to allow them to cross.
Pedestrians who rely on nonvisual information traditionally determine sufficient
gaps by listening for a period with no sounds of approaching vehicles (Allen, Courtney-
Barbier, Griffith, Kern, & Shaw, 1997; Jacobson, 1993; LaGrow & Weessies,
1994; Pogrund et al. 1993). Sixty years ago this was apparently an effective strategy.
Orientation and mobility (O&M) specialists at that time used a version of the timing
method for assessing the detection of vehicles to prove to apprehensive blinded veterans
that, when it was quiet, all the approaching vehicles could be heard from far enough
away (Sauerburger, 1999a).
Today, however, it is not possible in many situations to hear approaching traffic clearly
enough to know if it is safe to cross (Brennan, 2001; Snook-Hill & Sauerburger, 1996).
At busy roundabouts, masking sounds compromise the ability to hear approaching traffic
sufficiently (Wadhwa, 2003); in other situations, traffic sounds can be blocked by a hill or
a bend in the road, making it impossible to hear the traffic well enough even when it is
quiet (Sauerburger, 1989, 1995, 1996, 1999 a and b?), and sometimes, for no apparent reason,
the traffic is not sufficiently audible. At any given intersection, the ability to hear the
traffic can vary for reasons such as wet versus dry pavement, wind, ambient sounds, temporary
blockage of sounds by parked trucks or signs. Thus, it may be possible to hear the
traffic from far enough at one time, but not another. People who rely on normal vision also
are sometimes unable to know whether the gap is long enough for crossing because they
cannot see the traffic far enough, perhaps because of a hill or bend in the road.
In teaching students about crossing at uncontrolled intersections, comprehensive
O&M instruction has three goals for its students:
1. To enable them to recognize the situations at uncontrolled intersections where
they cannot reliably determine a crossable gap in the traffic because they cannot hear
or see the traffic far enough away.
2. To understand the risks and issues involved in crossing at such locations.
3. To provide viable alternatives to use in situations in which they cannot reliably
detect a gap in the traffic.
In the sections that follow, I list, in terms of objectives, the skills and concepts that students
need to achieve each of the three instructional goals and suggest some teaching
strategies for reaching the objectives.
Objectives for Meeting Instructional Goals
For Goal 1: The student recognizes situations at uncontrolled crossings where he or she
cannot reliably determine crossable gaps in traffic.
1. The student will be able to determine the width of unfamiliar streets by learning
the width of lanes that is typical for most streets
to determine how far away the passing vehicles are,
the typical geometry of streets, and
how to use this information to determine the probable width of unfamiliar streets.
2. The student will accurately predict crossing time for streets of various widths by
learning to accurately determine the distance to walk across each lane, and
understanding and predicting the necessary crossing time.
3. The student who has functional hearing or vision will understand how to use hearing
or vision effectively to detect gaps in traffic by
learning how the sound of approaching traffic is masked by other sounds and
blocked or muffled by obstacles, hills, and bends in the road.
learning the effects of lihting and other factors on their ability to see approaching
traffic and how to scan and glance for vehicles efficiently.
recognizing whether the traffic in given situations is detected better with vision
or with hearing.
4. The student will recognize situations at uncontrolled crossings where he or she cannot
hear or see well enough to reliably determine crossable gaps in traffic.
For Goal 2: The student understands the risks and issues involved in crossing streets
independently when he or she cannot reliably determine crossable gaps in traffic.
1. The student will understand the pedestrian and white cane laws regarding right-of-way.
2. The student will consider the probability that a vehicle that was undetected at the
beginning of the crossing would reach the student before he or she has finished the
crossing.
3. The student will understand the likelihood that drivers will slow down or stop to
avoid hitting the student. The student
learns about drivers’ needs for sight distance, braking time, and good road
conditions,
learns information from studies of the yielding behavior of drivers, and
observes the yielding behavior of drivers in the student’s area.
For Goal 3: The student demonstrates knowledge of and ability to use viable alternatives
for independent street crossing in situations where he or she cannot reliably detect
gaps in traffic.
1. The student will name six alternatives (listed below) to use if the risk of crossing
streets independently is unacceptable.
2. The student will execute the alternatives to independent street crossing at risky
situations.
The Alternatives
Cross at another place where the student can hear or see the approaching traffic
better.
Cross at a place that has traffic control. In streets with multiple lanes going the
same direction, traffic that is bunched together in a “platoon” followed by gaps
in traffic usually indicates that there is a traffic signal upstream—the closer the
traffic is bunched, the closer the traffic signal.
Get assistance to cross. Creative and effective ways to get assistance include
recruiting drivers to get out of their vehicles and guide the person across, going
to bus stops or public buildings to request assistance, or calling ahead or using
a cell phone to request someone to come and help.
Achieve the goal without crossing. Among the options are getting a ride; taking
a taxi, bus, or paratransit; taking the bus to the end of the line and back to
avoid having to cross to or from the bus stop; shopping online, or having home
delivery.
Engineer alterations. Request the traffic engineer to install stop signs or traffic
signals or to make alterations such as raised crosswalks, humps or other traffic-
calming strategies, or bulbouts. Bulbouts are extensions of the sidewalk into the
street that usually cuts off a lane, which then is designated as a parking lane. This
can significantly decrease crossing distance as well as slow the traffic, often
transforming an unsafe crossing into one at which it is possible to hear the traffic
well enough to know when it is clear to cross. The installation of a traffic
hump about a half block east of an intersection at which it was not possible to
hear traffic from the east had a surprising positive effect on that intersection.
After the installation, all vehicles can be heard far enough away to know when
it was clear to cross, either because the drivers were going slower or they revved
their engines after passing the hump. Research may determine other effective
engineering interventions.
An alternative to use under specific conditions. The uncontrolled crossing must
meet all of the following conditions: the student can hear or see far enough to
know that it is clear to cross halfway; the student knows when he or she has
reached the middle of the road, and the student is able to turn around and return
to the curb.
While listening or looking for approaching traffic, the student starts to cross
when it is quiet or no traffic is seen coming. If the student sees or hears any
approaching traffic before reaching the middle of the street, he or she returns to
the curb. If no traffic is seen or heard approaching by the time the student reaches
the middle of the street, he or she completes the crossing.
NOTE: This strategy is not to cross to the middle and wait. In many situations,
waiting in the middle of the street would be extremely dangerous. The strategy
is to turn around if the student notices traffic approaching before he or she reaches
the middle of the road.
Teaching Strategies
Below are some suggestions for teaching the skills and concepts that a student who relies
on nonvisual information needs to meet the objectives of the three instructional goals.
1. Understanding the width of traffic lanes and accurately determine the walking distance
across each lane (Goal 1, Objectives 1 and 2)
Walk with the student across a quiet street or an area that is marked to represent traffic
lanes and tell the student when each lane starts and ends, to help develop the kinesthetic
sense to determine the width of each lane. Repeat until the student can walk across the
lanes and report accurately when the next lane starts. Congenitally blind students can
examine vehicles to become familiar with the width of cars and trucks and understand the
reason for needing a width that accommodates them. However, be aware that street lanes
are usually wider than those in parking lots, to allow traffic more room to maneuver.
2. Determining how far away the passing vehicles are (Goal 1, Objective 1)
Stand with the student facing a street with multiple lanes of traffic going in the
same direction. Tell the student in which lane a passing car is traveling; then have
the student independently identify the lanes of the passing vehicles until she or he
can do so accurately.
3. Learning the typical geometry of streets (Goal 1, Objective 1)
Explain that although there are many exceptions, most streets are symmetrical. A
street with two lanes going one way will usually have two lanes going in the other
direction. However, at busy intersections, an extra lane is often inserted for left-turning
traffic entering the intersection. Sometimes a street will have a parking lane on one side
of the street but not the other.
4. Determining the probable width of various streets (Goal 1, Objective 1)
Have the student listen to traffic and determine how many lanes away the nearest
traffic on the far side of the street is. In that way, the student can determine with a high
degree of probability how many lanes are on the near side of the street. For example,
if the nearest traffic going from right to left is in the third lane, there are probably two
lanes with traffic going from left to right. The student then uses knowledge of typical
street geometry to calculate how many lanes wide the street is likely to be. For example
if there are two lanes going from left to right, there are probably two lanes going
from right to left, making a four-lane street.
5. Understanding and predicting the length of time needed to cross (Goal 1, Objective 2)
NOTE: This is probably the most important skill that students need to be able to
determine if the traffic that they can hear or see is far enough away for them to know
it is clear to cross.
Ask the student to imagine crossing the street and start a stopwatch. On the basis of the
student’s actual crossing times, report when the time that the student needs to cross has
passed. It can be helpful to report when the student would have reached the second lane,
the third lane, the middle of the street, or the last lane. Do not simply count the seconds.
Although some students enjoy the challenge of accurately measuring the passage of seconds—
and doing so can be a fun additional exercise for them—they need to develop an
innate understanding of the passing of time during their crossings.
Once the student understands the length of time needed to cross, ask her or him to
imagine crossing the street, reporting when she or he starts the imaginary crossing and
when he or she would have reached the other side. Start a stopwatch when the student
reports that the imaginary crossing has begun and stop the watch when the student
announces completion of the imaginary crossing and compare this to the actual crossing
time. Continue the exercise until the student can accurately measure the time needed
to cross.
The ability to determine where in the crossing the student would be at any given
moment also can be taught by asking the student to imagine starting to cross and interrupting
at some point to ask where in the crossing the student then would be. This ability
will be helpful later, when listening or looking for approaching vehicles. It will
enable the student to predict where in the crosswalk she or he would be if she or he had
started to cross just before detecting the approaching vehicles (assuming that the driver
had not slowed down for the student).
6. Learning how the sound of approaching traffic is masked by other sounds and
blocked or muffled by obstacles, hills, and bends in the road (Goal 1, Objective 3)
Surprisingly, many students who must rely on auditory information to cross streets
are unaware that the sounds of approaching traffic can be affected by features such as
hills and bends in the road and that other sounds such as receding vehicles or traffic
movements at a nearby intersection or roundabout can reduce their ability to hear
approaching vehicles. In certain conditions, listening to approaching traffic to be aware
of the distance from which it can be heard is usually sufficient for students to learn this,
especially if they objectively measure their detection of the vehicles.
For example, they can compare the sounds of vehicles coming over a hill or around
a bend in the road with those coming along a straight, level street. Also, when it is
quiet, they can listen to cars approaching from a distance, and if a second vehicle is
behind the first or if a car is approaching from the other direction, they can notice that
when the second car is audible it is much closer than was the first vehicle when it was
heard. Sometimes, the second car is not detected until after the first vehicle has passed.
Many students have no idea why they did not hear the second car until it was so close;
they must be told that the sound of the first vehicle masked the sound of the second.
The Timing Method for Assessing the Detection of Vehicles (TMAD, outlined in the
Appendix) is an effective strategy for teaching the effect of various masking sounds.
Help the student use TMAD to measure objectively the detection of approaching vehicles
when traffic is quiet; then measure again the detection of approaching vehicles
when a steady noise is present, and compare the two times. The noise can be an environmental
one, if steady, such as a lawnmower, or the recording of a steady sound
played at various volumes.
7. Learning the effects of lighting conditions and other factors on the student’s ability
to see approaching traffic and how to scan and glance for vehicles efficiently (Goal
1, Objective 3)
As is the case when learning about the effect of masking sounds on the detection of
traffic, the TMAD can also be used to provide feedback for students who rely on vision,
to develop their awareness of various lighting conditions and viewing distances. With
experience, the students will also learn what kinds of vehicles are more difficult to see
(e.g., dark vs. light, reflecting glare). Students with visual field defects may need to
learn to glance or scan effectively. More information and suggestions may be found at.
http://www. Sauerburger.org/scanning.htm
8. Recognizing whether the traffic in given situations is detected better with vision or
hearing (Goal 1, Objective 3)
Ask the student to wait until it is quiet and then observe the traffic approaching from
one direction. Ask the student whether he or she heard that traffic before seeing it or
saw it before hearing it. Discuss why that was the case. In some instances, such as
when hills or bends obstruct views or when the lighting conditions make it difficult to
see the approaching vehicles, the student will hear the vehicles before seeing it. In other
instances, such as noisy conditions or when the lighting or angle of the approach makes
the vehicle highly visible, the student will see before hearing it . With practice, the student
should be able to determine whether vision or hearing is more efficient.
9. Recognizing situations where the student cannot hear well enough to detect gaps in
traffic at unconrolled crossings (Goal 1, Objective 4)
Once the student has learned to determine the street’s width and understands how
much time is needed to make a crossing, take the student to several intersections to
have him or her observe and try to judge whether the traffic can be heard or seen well
enough to know when in those conditions there is a gap long enough for crossing and
when the vehicles are appearing without adequate warning. Then use the TMAD to
provide feedback about the student’s judgment.
NOTE: Conditions such as masking sounds or lighting must remain relatively steady
long enough to test the student’s judgment with the TMAD. If the student judges the
situation and conditions then change during the test, he or she will not receive accurate
feedback about his or her judgment of that situation.
Repeat testing the student’s judgment and providing feedback under a variety of conditions
until he or she can accurately judge when the conditions are too poor to know
when it is clear to cross. The student should experience situations in which it is possible
to hear or see well enough to know whether it is clear to cross and ones in which
the student cannot tell. To test a variety of conditions, go to different intersections or
change the conditions at one intersection by using different masking sounds or objects
that block the sound or the view.
10. Understanding the pedestrian and white cane laws regarding right-of-way (Goal 2,
Objective 1)
Many people, both sighted and visually impaired, make erroneous assumptions
about issues such as who has the right-of-way, what pedestrians must do to gain the
right-of-way, what effect the white cane or dog guide has on the right-of-way, what the
white cane laws are, and whether it is legal for pedestrians to cross midblock. O&M
specialists should be thoroughly familiar with and teach their students the laws in their
state or province, as well as generalities about similar laws in other states and provinces
(Sauerburger, 1999b).
11. Assessing the probability that a vehicle that was undetected at the beginning of the
crossing could reach the student before the crossing is finished (Goal 2, Objective 3)
Streets where the student is unable to hear or see the approaching traffic far enough
away to know for certain that it is clear to cross can offer a wide range of probabilities
in which the student starts the crossing and an undetected vehicle approaches that
would have to slow down or stop to avoid hitting the student.
When a student finds a situation in which it is not possible to know reliably that it is
clear to cross, have the student consider the probability that when he or she starts to
cross, an undetected vehicle would approach that would have to slow down or stop to
avoid hitting the student. Students should understand that the probability of that happening
is greater at busy streets and at streets where the traffic is fast and cannot be
heard or seen until it is very close than at streets with little traffic or where the traffic
is slower and can be heard from farther away. They also need to know that at any given
intersection, even if the visual or audible conditions stay the same, the probability that
an undetected vehicle will approach when they start to cross may vary, depending on
the time and the day of the week.
Students with both vision and hearing impairments may need assistance from someone
with vision or hearing to analyze situations and assess the probability that a vehicle
might approach during their crossing. The assistor can indicate the movement of the
vehicles, by pointing to each one as it passes to indicate the speed and volume of the
traffic. By placing a hand on the assistor’s pointing hand, a person who was deaf-blind
gains an understanding of the typical traffic situation at that time of day to determine
how likely it is that, as he or she starts to cross, an undetected vehicle will approach
that will have to slow down or stop to avoid hitting him or her.
12. Understanding the likelihood that drivers will slow down or stop to avoid hitting the
student (Goal 2, Objective 3)
Teach the student about drivers’ need for sight distance, braking time, and good road
conditions. The student should realize that when drivers see something in their path,
they require several seconds to react and start to brake and more time to bring the vehicle
to a stop. The student also needs to understand that drivers are less likely to take the
action necessary to slow down or stop in time to avoid hitting pedestrians, even those
with white canes, who are not crossing where drivers expect them to cross. In many
states, pedestrians with white canes who are not in crosswalks do not have the right-ofway
(Sauerburger, 1999b). In addition, the student needs to understand that, in some
road conditions, such ice or light rain on roads that have been dry for a long time, drivers
are unable to control their vehicles and slow down or come to quick stops.
The student can benefit from information reported in recent studies of the yielding
behavior of drivers. Studies by Geruschat and Hassan (2005) and Ashmead, Guth,
Long, Wall, and Ponchilla (2005) indicate that with all else being equal, the willingness
of drivers to yield tends to decrease as their speed increases, and drivers tend to yield
more in locations that normally have lots of pedestrian traffic.
On the basis of observations at crosswalks at an uncontrolled street at a residential
intersection near downtown Kalamazoo, Michigan; at a single-lane roundabout in residential
Tampa, Florida; and at a mid-block crosswalk on the campus of Western Michigan
University, drivers’ yielding behavior seems to be influenced more by the conditions
of the intersection than by the presence of a cane or dog (Ashmead et al.). Studies by
Geruschat and Hassan and Guth et al.suggest that in situations where almost all drivers
stop for pedestrians, using a white cane or guide dog makes no difference. Also, using
a white cane made no difference at the residential intersection in Kalamazoo where
almost none of the drivers stopped for pedestrians. In other situations, using a cane or a
dog improved the yielding behavior, but not enough to be reliable. At roundabouts in
Maryland, when only 9% of drivers yielded to pedestrians with no cane, 31% yielded to
pedestrians with a white cane, and 60% of drivers yielding to pedestrians with no cane
changed to 76% with a cane (Geruschat & Hassan). In the study by Guth, et al., the possibility
of drivers yielding in a 3-minute period changed from 15% for pedestrians with
no mobility aid to 32% for pedestrians with a white cane or dog guide.
In general, the percentage of drivers yielding for pedestrians who are standing at the
curb with no cane or dog at crosswalks at roundabouts in Maryland ranged from 5%
to 93%, and for pedestrians with a cane at those same crosswalks, the range was 31%
to 91% (Geruschat & Hassan). When two people, each with a cane or dog guide, stood
at a crosswalk in an exit lane at a roundabout in Maryland, with one of them placing
her foot in the street and reaching out her cane and tapping it, 11% of the drivers
stopped. Only 17% of drivers stopped when high-visibility pedestrian signage (including
a knock-down sign in the middle of the crosswalk) and 3 rows of sound strips
(bumps) were installed (Inman, Davis, & Sauerburger, 2006). When I stepped into a
crosswalk and tapped a white cane in separate right-turning lanes in Maryland and
California in 2003, about 50% of the drivers yielded (http://www.sauerburger.org/
dona/yielding.htm).
Finally, have the student observe the yielding behavior of drivers in the student’s
area. This information may be more applicable to the student’s situation than the
results of studies in other areas. Have the student try to get drivers to yield in various
situations and observe (with sighted assistance if necessary) how many drivers
comply. Make sure the student understands not to trust the verbal assurance of drivers
or others that it is safe to cross and to be aware of the dangers of crossing multiple
lanes when only one lane is blocked with a yielding vehicle. The presence of
that waiting vehicle reduces the visibility of the pedestrian to other drivers and
reduces the ability of the student to hear other approaching traffic (see Strategy 6 for
teaching Goal 1, Objective 3).
13. Using alternatives to independent street crossing at risky situations (Goal 3, Objective
2)
Have the student execute spontaneously planned alternatives. For example, have the
student approach an intersection and evaluate the crossing. If the student cannot hear
or see the vehicles well enough, have the student consider the feasibility of various
alternatives and implement one that does not require planning ahead, such as getting
assistance or crossing elsewhere.
Assign the student to go to destinations in familiar areas that have intersections
where the student knows he or she cannot hear or see the vehicles well enough and plan
a route to avoid those intersections.
Have the student contact traffic engineers responsible for troublesome intersections
to consider the feasibility of revising the intersection or surrounding areas to make it
safer to cross.
Conclusion
O&M students should be prepared to assess and make decisions about crossing
streets with no traffic control. The concepts and skills outlined here can enable them to
do so and are necessary for safe, independent travel in many areas. Instructors can
introduce these skills and concepts as soon as the student is ready to consider crossing
streets; some of the concepts can be introduced to children before they are old enough
to learn to cross streets independently. It seems to make no difference whether the student
learns how to cross without traffic controls before learning how to cross at signalized
intersections, or vice versa.
Although these skills and concepts can be taught in any order, learning to recognize
situations where the student cannot sufficiently hear or see oncoming traffic has several
prerequisites: (a) determining the width of the street (Goal l, Objective 1 and Strategy
4), (b) determining the time needed to cross the street (Goal 1, Objective 2 and Strategy
5), (c) understanding the effects of masking sounds and other environmental factors
on the ability to reliably detect the vehicles (Goal 1, Objective 3 and Strategy 6), and (d)
the distance from which the student can see or hear the vehicles (Goal 1, Objective 4 and
Strategy 7). In addition to having learned to analyze situations and risks, the independent
traveler must also be able to make decisions about street crossings, such as considering
how much risk is acceptable and when it is preferable to look for alternatives.
REFERENCES
Allen, W., Courtney-Barbier, A., Griffith, A., Kern, T., & Shaw, C. (1997). Orientation and
mobility teaching manual (2nd ed.). New York: CIL Publications.
Ashmead, D., Guth, D., Wall, R., Long, R., & Ponchillia, P. (2005). Street crossing by sighted
and blind pedestrians at a modern roundabout. Journal of Transportation Engineering, 131, 812–821.
Brennan, T. (2001). The blind leading the blind. Nacagdoches, TX: Author.
Geruschat, D., & Hassan, S. (2005). Driver behavior in yielding to sighted and blind pedestrians
at roundabouts. Journal of Visual Impairment & Blindness, 99(5), 286–302.
Inman, V. W., Davis, G. W., & Sauerburger, D. (2006). Pedestrian access to roundabouts: Assessment
of motorists’ yielding to visually impaired pedestrians and potential treatments to
improve access (Federal Highway Administration Report DTFH61-002-OC-00064). McLean,
VA: Federal Highway Administration.
Jacobson, W. (1993). The art and science of teaching orientation and mobility to persons with
visual impairments. New York: American Foundation for the Blind.
LaGrow, S., & Weessies, M. (1994). Orientation and mobility: Techniques for independence.
Palmerston North, New Zealand: Dunmore.
Pogrund, R., Healy, G., Jones, K., Levack, N., Martin-Curry, S., Martinez, C., et al. (1993).
TAPS—An O&M curriculum for students with visual impairments. Austin, TX: Texas School
for the Blind and Visually Impaired.
Sauerburger, D. (1989). To cross or not to cross: Objective timing methods of assessing street
crossings without traffic controls. RE:view, 21(3), 153–161.
Sauerburger, D. (1995). Safety awareness for crossing streets with no traffic control. Journal of
Visual Impairment & Blindness, 89(5), 447–450.
Sauerburger, D. (1996). Teaching and assessing judgment for crossing streets where there is no
traffic control [videotape]. Contact the author to obtain a copy.
Sauerburger, D. (1999a). Developing criteria and judgment of safety for crossing streets with
gaps in traffic. Journal of Visual Impairment & Blindness, 93(7), 447–450.
Sauerburger, D. (1999b, September). Rules of the road. Metropolitan Washington Orientation
and Mobility Association Newsletter, 2–3.
Sauerburger, D. (2003, March). Do drivers stop at unsignalized intersections for pedestrians who
are blind? Paper presented at the conference of the Institute of Transportation Engineers, Fort
Lauderdale, FL
Snook-Hill, M., & Sauerburger, D. (1996). Teaching students to assess safety for crossing streets
which have no traffic control. Proceedings of the International Mobility Conference, No. 8
(pp. 535–540). Tambartun National Resource Centre, Melhus, Norway.
Wadhwa, L. C. (2003, January). Roundabouts and pedestrians with visual disabilities: How can
we make them safer? Paper presented at the conference of the Transportation Research Board,
Washington, DC.
APPENDIX
Timing Method for Assessing Detection of Vehicles
The Timing Method for Assessing the Detection of Vehicles (TMAD) is used as a tool in some
of the teaching strategies, particularly strategies 6 and 7. The TMAD answers the question: “Can
I see or hear vehicles far enough away to know when it is clear to cross?” The TMAD can also
be used to help students understand the way that environmental factors such as ambient noise and
glare affect their ability to hear or see the traffic. Before introducing students to the TMAD, they
should have a clear concept of how much time they need to cross streets.
Procedure
1. Have the student determine the time needed for the crossing either by estimating on the
basis of walking speed and the width of the street or timing several crossings and using the
longest time. Do not use the average time; you are looking for the worst-case scenario.
2. Have the student stand at the edge of the street, waiting until he or she detects no approaching
vehicles (a perceived lull in traffic). If the student depends on hearing, this should be at a
time when he or she thinks it is quiet enough to hear approaching traffic well enough to know it
is clear to cross.
3. Start a stopwatch when the student sees or hears something that might be an approaching
vehicle.
4. Stop the watch when the approaching vehicle passes in front of the student. If the time
recorded is less time than he or she needs to complete the crossing, then you know that even if
the student had started to cross just before detecting the vehicle, it would have reached him or
her before the crossing was finished. If the recorded time is longer than the student’s crossing
time, he or she would have completed the crossing safely even if he or she had started just before
detecting the vehicle.
5. Continue timing the student’s detection of approaching vehicles until you have taken sufficient
samples to conclude whether the student can detect all vehicles well enough to know
when it is safe to cross there.
If you started the timer the instant the student first detected anything that might possibly be a
vehicle, yet a vehicle reached the student in less time than he or she needs for crossing, there is
no need to continue. You now know that under those conditions it is not possible to detect all the
vehicles in the time the student needs for crossing, and the student should consider alternatives or
be aware that if crossing there, he or she is depending on drivers seeing and avoiding him or her.
If the student detected all the vehicles, including one of the “worst cars” (a vehicle that, once
detected, reaches the student in the shortest time) with enough warning to allow time to cross, then
you can conclude that he or she can cross there safely under those conditions. Because you need
to know whether even the worst cars can be detected with enough warning, continue to time the
detection of approaching vehicles until you are satisfied that you have timed the approaching vehicles
until you are satisfied that you have timed the approach of at least one of the worst cars. That
is, continue timing until you are confident that if you timed the approach of any more cars, you
would be unlikely to find one that reached you in less time than the cars already observed.
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