CROSSINGS WITH NO STOP SIGN OR TRAFFIC CONTROL
Situations of Uncertainty for Gap Judgment
Situations Where You Cannot Be Certain It Is Clear to Cross
SUMMARY: Today, you can be confident that it is clear to cross in many situations,
there are many situations where you can never be certain it is clear to cross.
At some places these situations of uncertainty exist
even when it is very quiet or you can see nothing coming.
The only way to recognize these situations is to
observe and analyze each street-crossing situation.
Our students who cross streets must to be able to RECOGNIZE THOSE SITUATIONS.
What is a "situation of uncertainty for gap judgment"?
It is a situation where you cannot be sure whether it is clear to cross.
Situations of uncertainty for gap judgment -- yesterday and today
This is because you cannot hear/see the traffic well enough to know whether a vehicle is coming that could reach you before you finish your crossing
that is, you don't know whether there is a gap in traffic long enough to allow you time to cross (a "crossable gap").
At some places, there is a situation of uncertainty even when it is quiet or you see nothing coming.
Sixty years ago, when the orientation and mobility profession was established, it was always clear to cross streets whenever it was quiet (Sauerburger, 1999).
Heck, if there were any vehicles coming that could have reached you before you finished your crossing, you would have heard them!
Verified with research
Today, that is still true at some crossings. At these crossings, you can hear/see all the vehicles well enough that:
But this is NOT true at all crossings today. Today, there are some crossings, including some crossings at quiet, narrow residential streets, where you can't hear the cars well enough to be sure it's clear to cross, even when it's quiet.
And I'm not just talking about being unable to hear electric cars and hybrids, I'm talking about being unable to hear any cars well enough to know it's clear to cross when quiet.
- If something were coming that would reach you during your crossing, you'd hear/see it!
- In these situations, whenever it is quiet (or whenever you see nothing coming), you know it is clear to cross.
Dr. Rob Wall Emerson and I did some research at three quiet residential streets where the crossing had no traffic control (Wall Emerson, R. and Sauerburger, D., 2008).
At one of those streets (left photo), the situation was the same as it had been 60 years ago.
Blind people WERE able to hear all the vehicles
well enough to know that whenever it was quiet, it was clear to cross.
This was true regardless of
-- how quiet the cars were (some were as quiet as 58 dBA) or
-- how fast they were going (some were going over 50 mph).
But at one two-lane residential street (right photo and in the video below)
, even when it was very quiet, experienced blind travelers with normal hearing were unable to hear some of the approaching cars
until the cars were only 4 seconds away!
Four seconds isn't long enough to cross the street, so in that situation
they could never be sure whether they had enough time to cross, even when it is very quiet.
Therefore that was a situation of uncertainty for gap judgment
Do you want to see it for yourself?
Below are videos of situations where it is not possible to hear OR see the approaching cars far enough to know whether it is clear to cross.
In these situations, whenever it is quiet and you can hear or see nothing coming and start to cross, there might be a car just over the hill or around the bend that would have to slow down to avoid hitting you.
In both situations there are only 5-6 seconds from the time the approaching cars are seen until they arrive, and the cars can not be heard until they are about 4 seconds away.
Below: 4-lane crosswalk in front of a high school (10 seconds crossing time) -- see Vignette #1 for a sample lesson here.
Description: We are looking to our right; the car is first seen and heard when it comes over the crest of a hill from about a half block away, and arrives at the crosswalk 6.5 seconds later.
Below: Crossing on a residential two-lane street, 25 mph speed limit (7 seconds crossing time)
Description: We are looking to our right; the car can be seen coming around a sharp bend about 30 yards away and arrives almost 6 seconds later.
How can we recognize if we are in a "situation of uncertainty for gap judgment"?
The only way to determine if you are in a situation of uncertainty for gap judgment is to observe and analyze how well you can hear / see the traffic in that situation.
There are no rules that reliably predict whether we are in a situation of uncertainty for gap judgment.
Not even rules that seem intuitive, such as "it is safe to cross 2-lane streets when it is quiet but not 3-lane streets."
Or "it is safe to cross where the street is straight and visible for a long distance when it is quiet, but not where there is a bend or hill nearby that could block the sound of traffic."
Or "it is safe where the traffic is slow but not where it is fast." NONE of these rules are reliable -- none of these rules can predict whether you will have a situation of uncertainty!
I will illustrate this with a story. Many years ago, I was looking for a street-crossing situation for my client to analyze.
She had already analyzed a place where it wasn't possible to hear the cars far enough away (a situation of uncertainty for gap judgment), so I was looking for a place
where she COULD hear the cars well enough to know it is clear to cross whenever it is quiet.
I chose the crossing in the photo to the left. It was perfect!
The road was narrow (only 2 lanes), the speed and traffic volume were low, and there was nothing blocking the sound of traffic -- I could see the traffic approaching from quite a distance.
So I brought her there for our session. As she listened to the traffic to figure out how wide the street is, she quietly said, "I can't hear the cars well enough here to know if it's clear to cross."
That session was videotaped, and I still chuckle when I see my face showing the shock and disbelief that I felt when she said that.
I thought, "This can't be true!"
So I listened, and sure enough -- she was right! I could see the cars coming but neither of us could hear them until they were about 5 seconds away.
Since that time, I've seen several other streets with the same situation -- there is nothing blocking the sound of the cars but you cannot hear them until long after you can see them. Perhaps it because of the pavement surface, or something absorbing the sound -- we don't know why.
Anyway, don't take my word for it!
Find out for yourself -- see how well you can predict which of the situations in the "Uncertainty Prediction Challenge" show a situation of uncertainty for gap judgment (click here for the "Challenge").
Can we rely on guidelines to identify situations of uncertainty for gap judgment?
How did you do on the Uncertainty Prediction Challenge?
Was it easy to predict when there is a situation of uncertainty for gap judgment?
If you say, "No WAY!" then join the club!
And THAT is exactly the point!
NO ONE can predict when there is a situation of uncertainty for gap judgment.
What I hope you learned from taking the Challenge is that:
THERE ARE NO HARD-AND-FAST RULES
FOR FIGURING OUT
WHETHER YOU ARE IN A SITUATION OF UNCERTAINTY FOR GAP JUDGMENT!
- Sometimes a sharp bend in the road nearby makes it impossible to hear all the vehicles well enough (such as at Photo #3), but sometimes a sharp bend nearby is not a problem (Photo #2).
- Sometimes it is possible to hear the vehicles long before they can be seen (such as Photo #2) and sometimes it is possible to see them long before they can be heard (such as at the street in Photo #5 and in the video below).
- Sometimes a situation of uncertainty for gap judgment exists even though the traffic is slow (Photo #3), and sometimes even though the traffic is fast it is possible to hear them far enough to know it is clear to cross whenever it's quiet (as shown in Photo #1 and Photo #2).
- Sometimes conditions can change so that you can hear the vehicles well enough at one
time, but not at another. For example:
- When the roads are wet, traffic can be heard better than when they are dry.
- A small change at the street in Photo #5
made it possible to hear well enough to know it is clear to cross whenever it is
quiet (see "Environmental Modifications").
- Parked vehicles created a situation of uncertainty for gap judgment because they blocked the sound of traffic at the street in Photo #6.
And yet in our research, when we placed a barrier between blind participants and the traffic (see photo), it didn't seem to impair their ability to hear the vehicles significantly (Wall Emerson & Sauerburger, 2008).
So the presence of something that might block the sounds is not a reliable indicator as to whether there is a situation of uncertainty for gap judgment either.
We don't know all the conditions that can affect the sound:
Dr. Rob Wall Emerson and I studied the factors that might affect the ability of blind pedestrians who have normal hearing to hear approaching vehicles (click here for the article). We collected data regarding
Analysis of the data indicated that these factors altogether accounted for only a third of the variability in people's ability to hear the vehicles approaching.
Based on the fact that the blind participants in this study were able to hear all the vehicles with enough time to be able to complete a crossing in some places but not in others,
and the fact that the factors studied did not adequately predict the situation, we concluded that pedestrians who are blind ...
- how quiet or noisy the conditions were when the blind participants first heard the vehicle;
- the sound level of the vehicle itself and its speed; and
- the presence of blockage or hills / bends in the road.
"...need to be aware that before they can assume that it is clear to cross when quiet in a given situation,
they must first observe their ability to hear the vehicles in that situation and
determine whether they can hear well enough to know that it is clear to cross."
(Wall Emerson, R. & Sauerburger, D., 2008, page 760
Example of misleading situation -- impossible to predict!
These videos were taken by Rikilynn and Paul Layher (both COMS) with their student, analyzing a crossing in rural Michigan.
This crossing is a wonderful example of a situation that is different from what you would predict.
For some strange reason that we can't figure out, you can see the approaching vehicles for a very long time before you can hear them.
This example illustrates the principle that ...
...the ONLY way to determine if a situation is uncertain for gap judgment is to ... what was that again?
observe and analyze how well you can hear / see the traffic in that situation, as Rikilynn and her student did!
So what? How does this affect what we Orientation and Mobility Specialists teach?
There is now consensus that:
best practice is for O&M instructors to teach
their students to be able to recognize situations of uncertainty for gap judgment
(that is, recognize situations in which they can not assume that it is clear to cross whenever quiet, or whenever they see no vehicles approaching).
This consensus of best practice was asserted in 2008, when the O&M Division of AER approved a position paper
which states that
Thus it becomes incumbent upon us to follow established best practice and address these issues with our students, teaching them the skills and concepts they need to deal with modern crossings.
- the traditional strategy for crossing streets with no traffic control ("assume it is safe to cross when quiet") is no longer dependable;
- O&M programs must ensure that consumers who are blind or visually impaired are able to
- determine whether they can recognize gaps in traffic that are long enough to cross, and
- determine the level of risk for crossing (including the likelihood that vehicles could reach them and the likelihood that drivers will yield to them).
So, how can we teach our students about crossing with no traffic control?
How can we teach our students to recognize situations of uncertainty for gap judgment when there are no reliable guidelines other than careful observations and analysis of their ability to hear or see the vehicles in each situation?
I have been working on this problem with my students for 20 years.
During this time, my understanding of the issues has slowly evolved, and so have my instructional strategies, explained in Journey to Understanding (to find out what inspired this work, click here).
For a list of all the skills that seem to be necessary, as well as suggestions for teaching them . . .
Wall Emerson, R. & Sauerburger, D (2008). "Detecting approaching vehicles at streets with no traffic control." Journal of Visual Impairment and Blindness, AFB Press, Volume 102, Number 12, pp. 747-760
This webpage was developed from a poster that was graciously hosted on the SpEdEx website
my heartfelt appreciation to SpEdEx webmaster Ray Dragon!
Return to Crossing Streets Where There Is No Stop Sign or Traffic Signal
Return to Self-Study Guide: Preparing Visually Impaired Students to Assess and Cross Streets with No Traffic Control
Return to home page