Commentary
The Fallacy of the Timing Methods
Jane D. Bennett
Editor's note: Commentary provides an opportunity for the expression of individual views on issues in the field of rehabilitation and education of those with visual impairments.
The Editors invite responses to these articles and encourage readers to submit commentaries on issues of concern.
Visually impaired persons increase their safety while crossing city and suburban streets by using white canes and crossing at controlled intersections.
If the crossing is uncontrolled, a decision involving many subjective variables must be made concerning the safety of such an undertaking.
Dona Sauerburger in RE:view, Volume XXI, No. 3, has proposed reducing this subjectivity by using objective timing methods. I consider these methods to be based on an incorrect assumption and to be, therefore of limited use.
Timing methods may be valuable in teaching travelers when "not [italics added] to cross" an uncontrolled crossing, which I define as any situation, including intersections, in which the vehicular traffic perpendicular to the pedestrian's line of travel has the right of way.
They cannot be used to determine a safe crossing.
Summary of the Timing Methods
When describing the Timing Method of Limited Detection (TMLD) and the Timing Method of Unlimited Detection (TMUD), Sauerburger advocates repeating the timing of a visually impaired traveler's street crossing to determine "the 'required crossing time' [that] should be the longest time recorded" (p. 154).
In the TMLD the visually impaired pedestrian should then measure the amount of time between the detection and the arrival time of a motor vehicle.
The timing of cars from both directions should be repeated "several times until the instructor feels certain of having timed at least one of the vehicles that arrives in the shortest time" (p. 154).
Sauerburger then takes the speed of the fastest of those vehicles; and if the pedestrian's required crossing time is less, it appears that she would consider it a safe crossing.
Sauerburger feels that such timings provide the objective information needed to facilitate making that subjective decision at uncontrolled crossings.
The main distinction Sauerburger makes between limited and unlimited detection timing methods refers to the degree of visual acuity the pedestrian has.
"Visually impaired people who can see far" (p. 157), with unlimited detection, could refine the method of timing cars by using TMUD.
The pedestrian "starts a stopwatch when he thinks that the nearest vehicle is just barely far enough away to enable him to finish crossing that part of the street before the vehicle could reach him" (p. 156).
The Incorrect Assumption
How can one know if the fastest car has been timed? One cannot know for sure. Is being "reasonably" sure good enough?
Who says all car drivers are "reasonable"?
From Sauerburger's data it is possible to decide only which of the cars measured so far was the fastest.
By timing "several" cars should pedestrians feel "certain" they have timed one of the fastest?
No assumptions can safely be made by pedestrians about what a driver of a given vehicle will do. Cars speed excessively, change lanes, speed up, slow down, and even stop, often causing the driver of the car behind to react unpredictably.
Because these actions are usually unexpected maneuvers for pedestrians, the results can be disastrous.
Once the pedestrian, using the TMLD or the TMUD, decides to cross, what if the next car, or any succeeding car, speeds by in less time?
It seems the pedestrian most probably will be hit or just missed by the vehicle.
What exactly is a "reasonable" number of cars to time?
Sauerburger only suggests "several" (p. 154).
Would timing not 15 but rather 50 or 500 or 5,000 vehicles be enough?
How many people would bother to wait so long?
Yet if told that one random car out of the next 50,000 vehicles -- and it might be the very next one -- will definitely hit and injure or kill them, most people would decide to detour, even if "inconvenienced."
The answer to questions concerning the safety of crossing any uncontrolled intersection is subjective at best; a value judgment must be made whether or not to cross.
I think using either the TMLD or TMUD is, in effect, playing Russian roulette. When teaching this timing method, orientation and mobility instructors are playing with someone else's life.
No matter how many cars are timed, the data gathered are only correct timings of cars that have passed, not of cars yet to pass.
Therefore the data will always remain incomplete.
No sample of timed cars can ever be sufficient. If the visually impaired person is made to feel that "several" correctly timed cars are a reliable component in the complex decision-making process, eventually a judgment will be flawed.
A False Assumption Can Lead to False Sense of Security
Decisions about crossing a street reflect the value clients place not only on their independence but also on their lives.
Safety awareness is of great importance, and I contend that it is irresponsible for an orientation and mobility professional to teach techniques that imply a crossing is "safe" when they are based upon incomplete data.
An orientation and mobility instructor cannot tell any client that a specific crossing is "safe."
The instructor can only emphasize to clients that they can make relatively safer crossings by factoring certain risks into their decisions.
Showing visually impaired people how to use correct data in an illogical manner provides them with a false sense of security.
Their trust in such information and in the orientation and mobility professional can easily be diminished with the appearance of that next "fastest," and maybe deadly, car.
After discussing the subjective variables involved in a good crossing -- for example, time of day, weather conditions, lighting, absence of sound and visual shadows, physical and visual attributes of the client (such as hearing, walking speed, acuity, visual fields, contrast sensitivity), as well as the apparent speed of cars and traffic conditions
-- I instruct my clients how to cross streets in the safest known way.
Practice during lessons reinforces the instruction.
The clients not only comply but also usually appreciate the logic of this professional reasoning.
Once orientation and mobility lessons have been completed, my clients should have attained their goals of developing good safety awareness and learning how to assess for themselves the risks in diverse situations.
How clients ultimately cross streets is obviously their choice.
Sauerburger stresses that these "decisions ... are subjective, no matter how much objective information about that crossing is available" (p. 160).
Although she qualifies her positions with indefinite words like "several," she also uses words such as "certain" (p. 154), "safely" (p. 154), and "fastest" (p. 155).
Her methods can never be "certain" nor can they ensure that the client "safely" crosses the street.
Emphasizing and focusing on incomplete objective information gives an incorrect sense of security and well being.
No crossing is 100% safe, even if the pedestrian factors all the risks and waits for silence.
Many visually impaired people could easily come to rely on timing methods and to ignore the other sensory inputs and the common sense needed to travel safely.
When told that timing some number of cars makes a crossing "reasonably safe," students may remember only the word "safe," but not the modifier "reasonably."
Informal timing methods, on the other hand, do not lead to a false sense of security.
Adventitiously impaired adults usually have successfully negotiated uncontrolled street crossings for many years when they had good sight.
With them I find little need to employ a stopwatch for measuring time and distance because they are now visually handicapped.
Given good hearing, most seem correctly to process the many complex variables involved.
From experience they know how much time is needed to cross, even if using a support cane, and are able to judge if the approaching car they see or hear is too close.
They learn to go only if they hear no car approaching from either direction, keeping in mind that some cars are very silent.
In the absence of such conditions, they know to make an alternate decision.
On the other hand, congenitally visually impaired persons, those with a hearing loss and/or other physical handicaps, or individuals functioning at a lower travel level, often have to be taught how complex a crossing can really be.
Timing Method -- When "Not to Cross"
If inexperienced visually impaired persons continue to insist that they can or want to cross a street in a location where the orientation and mobility instructor considers the risk too great, objective timing methods might indeed furnish proof of the imminent danger.
Timing themselves and approaching cars might help them to understand that a car, arriving at the crossing in 8 seconds after being detected, will cause problems for pedestrians who can cross in only 9 seconds.
The pedestrians might make it across only if the driver sees them and avoids them or can stop soon enough.
Thus, although clients rarely need such a vivid demonstration to be convinced a crossing is unsafe, they could effectively use this timing technique to prove to themselves the danger of their original decision.
Timing just one "too fast" car can help determine when "not to cross."
Additional concerns
Running across a street
Sauerburger says, "People who initially think it is safe to cross when the vehicles are too close may be judging the vehicles based on a habit of running across these kinds of [uncontrolled] streets.
If this is the case, the orientation and mobility instructor should discuss with them whether in their particular case it is safe to run.
If so, the instructor should time the crossing accordingly [italics added]" (p. 158).
And also, "If it is not too risky, the pedestrian may determine that there will be enough time to reach the other side safely if he or she crosses at a narrower part of the street or walks faster or runs [italics added] across the street." (p. 155).
I feel that teaching or implicitly allowing anyone to run across a street is irresponsible.
If visually impaired persons insist on running across a street, that is their own business, but I will not imply it is safe and will not practice or implicitly support it during lessons.
Picking a landmark
On page 160 Sauerburger writes, "Another woman with a large visual field did not improve her judgment of the speed and distance of oncoming traffic, even after practice and discussion of the TMUD.
She then chose as a landmark a driveway from beyond which, according to the TMUD, even the fastest [italics added] vehicle could not reach her before she finished the crossing.
She would start her crossings only when the nearest vehicles was farther away than that driveway; she then could cross the street safely in spite of her inability to judge the vehicles."
It can be virtually impossible for anyone to determine accurately whether a car has actually passed a given distant landmark.
Even if a car's relationship to a landmark were "reasonably" easy to detect, one's ability to judge the speed of a car combines auditory and visual perceptions:
perceptions made at a distance and thus subject to environmental maskings and distortions.
It is also important to realize that the driver might speed up after passing the landmark, perhaps to take advantage of a green light a block or two away.
Conclusion
Do orientation and mobility professionals have a right to use methods based on a flawed assumption?
Should fallacious timing methods be used for assessing street crossings where there is no traffic control?
To provide the client with "as much objective information as possible" (p. 160) concerning a street crossing is a laudable goal, but only if the assumption behind the objective information is valid.
Jane D. Bennett is an AER-certified orientation and mobility specialist at the U.S. Department of Veterans Affairs, Western Blind Rehabilitation Center in Palo Alto, California.
Dona Sauerburger replies:
I am pleased that Jane Bennett has done such intense and productive thinking about the safety of crossing streets without traffic controls.
Our profession needs to direct more attention to developing ways of preparing blind and visually impaired persons for making decisions about intersections with no traffic controls.
A Flawed Assumption
Bennett objects to the timing methods of assessment because she concludes that they are "based on a flawed assumption."
When I first read her response, I thought that the flaw was that no matter how many vehicles were observed before making a conclusion, one could not be certain that there could never be a car that was more dangerous than those observed.
Bennett says in a variety of ways, "No matter how many cars are timed, the data gathered ... will always remain incomplete" (p. 76-77).
This statement is true whether one tries to quantify observations by timing the detection of vehicles or bases one's judgment on informal observations as she advocates (p. 77).
Bennett prepares her students for crossing at uncontrolled intersections by discussing an impressive list of variables, including "the apparent speed of cars and traffic conditions."
I assume that to do this she and the student observe conditions until they are reasonably certain of them.
How much observation is necessary before making a decision?
Bennett asks, "What exactly is a 'reasonable' number of cars to time [when using the timing methods to assess the conditions]?"
My query to her is how long was it reasonable for her and/or her student to observe traffic conditions before feeling confident enough to make decisions about the crossing?
Guaranteed Safety
Bennett says that it would be irresponsible for mobility instructors to tell students they can cross a street safely until they have gathered all the data, by which she seems to mean data not only of cars that were observed but "of cars yet to pass" (p. 76).
She explains (p. 77) that "no crossing is 100% safe, even if the pedestrian factors all the risks and waits for silence."
She states (p. 77) that "an orientation and mobility instructor cannot tell any client that a specific crossing is 'safe.'"
Perhaps then the flaw for Bennett is not drawing conclusions from inadequate data (everyone must draw conclusions and make decisions based only on what can be observed), but the "flawed assumption" actually may be that by using timing methods a student can be guaranteed to be safe crossing the street.
A safe crossing can never be guaranteed, whether the conditions are assessed informally or by using the timing methods.
In her response Bennett states (p. 77) that "[Sauerburger's] methods can never be 'certain' nor can they ensure that the client 'safely' crosses the street."
If any readers were left with the impression that using these timing methods can guarantee safety, or that people can obtain accurate assessments by applying the timing methods without thinking, or that by using timing methods they no longer need to use their other orientation and mobility techniques or their "sensory inputs and the common sense needed to travel safely," then I am grateful that she has given me the opportunity to correct this misunderstanding.
Several times Bennett mentions her concern that a car thought to be far enough away to permit a safe crossing may unexpectedly accelerate or be passed by a car going too fast to avoid hitting the person.
This possibility exists for anyone who must judge when it is safe to walk or drive a car across the path of oncoming vehicles.
A similar problem exists at an intersection with a traffic light.
As we are crossing when the light is green, a driver may turn a corner too fast or may run a red light.
Bennett feels that she can teach clients "how to assess risks for themselves in diverse situations" (p. 77), and that most adventitiously blinded people know from experience how to judge if approaching cars are too close.
However, she is not confident that visually impaired people can learn to judge when they need to be alert for the danger of accelerating or passing cars.
This incongruity and her apparently greater concern with the problems of making decisions at uncontrolled intersections than with those that may exist at a traffic light, reflect the fact that mobility instructors have more experience preparing clients to cross at traffic lights than at uncontrolled intersections.
Experience gives us confidence in the ability of clients to learn skills and develop a good judgment for crossing at a traffic light.
If we spent an equal amount of time preparing our clients to make decisions about crossing without a traffic light, perhaps we would gain a better understanding of what they could learn to do in those situations.
Running Across a Street
Some instructors assume that it is dangerous for anyone, blind or sighted, to ever run across any street under any conditions.
I do not know whether this is true or not.
In my article I did not argue for or against running but gave suggestions for situations if it was safe to run, and I stressed the word "if."
Obviously, this means that if one determines that in the given situation it is not safe to run, or assumes it is never safe to run, then one does not consider those suggestions.
Valuable Data to Weigh Against Assumptions
Bennett's first sentence reflects the assumption of many mobility instructors -- that it is always safer to cross at traffic lights than a uncontrolled intersections.
That assumption should not keep us from analyzing carefully the safety of such crossing and testing our preconceived assumptions.
To illustrate: A visually impaired person needs to reach a destination across a hypothetical street, and the nearest control for traffic on that street is a traffic light on a busy perpendicular street two blocks away.
One cannot assume that safety can always be increased by crossing at the controlled intersection.
If the street to be crossed is a quiet, narrow side street, and the person has no other handicap, most people would consider it safe to cross there and not only unnecessary but possibly more risky to go four blocks out of the way to cross at the light at the busy intersection.
In this scenario, even if we gradually make the street wider and busier and/or decrease the person's vision or hearing or physical or mental abilities, the street will for some time continue to be safe for that person to cross there.
At some point the street will become unsafe, and alternatives such as crossing at the light or asking for assistance must be considered.
What determines the point at which the street has become too wide and/or the traffic too dangerous and/or the person's abilities too limited to enable a safe crossing there?
I have found the timing methods of assessment very helpful in making this distinction; by using them, I have discovered that many of my former assumptions were incorrect.
That Bennett's students "not only comply but also usually appreciate the logic of [her] professional reasoning" (p.77) without using the timing methods does not mean that her reasoning is accurate. She has some of the same misconceptions that I had before I started using the timing methods to improve my observation and ability to judge.
1. Most adventitiously impaired adults with good hearing "learn to go only if they hear no car approaching from either direction, keeping in mind that some cars are very silent" (p. 78).
I have learned that the assumption that it is always safe to start crossing when it is perfectly quiet is a misconception.
We found a number of business and residential streets where, if depending on good hearing and starting to cross when it is quiet, a car that was undetected when a person started to cross could reach the person before he or she could reach the middle of the second lane.
2. "Given good hearing, most [adventitiously blinded adults] seem to correctly process the many complex variables involved.
From experience, they know how much time is needed to cross, even if using a support cane, and are able to judge if the approaching car they see/hear is too close" (p. 78).
I also had this misconception and rarely took the time to assess the abilities of such students to judge or detect vehicles at intersections with no traffic control.
I have found that other instructors across the country also did not direct much attention to this problem.
Having used the timing methods to help me assess students in a variety of situations, I have found that some naturally develop this ability, but some do not.
Many of those who had normal vision until recently judged it was safe to cross when the cars were in fact too close and too fast.
In my practice, I have found that the most practical use of the timing methods is not for the analysis of specific intersections, which is needed only occasionally, but for the assessment and, if needed, improvement of students' judgments of their own abilities and the conditions of the crossing.
Misunderstanding the Timing Methods and Their Use
Bennett's response shows that she does not fully understand the timing methods and their use. She states (p. 76) that the main distinction between the Timing Method for Limited Detection (TMLD) and the Timing Method for Unlimited Detection (TMUD) refers to the pedestrian's degree of visual acuity.
The main distinction is that each method provides different information.
If people need to know whether they can detect vehicles far enough away, they use the TMLD. If they need to know if they can judge the speed and distance of those vehicles, they use the TMUD.
In Picking a Landmark Bennett does not seem to understand that even the fastest cars we observed reached us from those landmarks with plenty of time to cross.
If a car speeds up only after passing the landmark, it will not be a concern because it will take longer to reach the person than the continuously speeding cars that have been timed.
In this situation, as the person prepares to cross, it is unnecessary to judge the speed of the cars, only to determine that the nearest one has not passed that landmark.
Bennett claims that it is virtually impossible to determine accurately when a car has passed a distant landmark (p. 79).
Is this an assumption or is her statement based on experience?
Contrary to her assertion, several of my clients with sufficient vision have done it satisfactorily and consistently.
The timing methods are not a substitute for careful analysis of the situation at street crossings.
They are tools to be used to help assess clients' abilities to detect vehicles or to assess or improve their judgments about the distance and speed of vehicles.
I would be interested to hear from readers who have tried the timing methods to learn if the instructions were sufficiently clear, if they found difficulties in using the methods, or if they have developed any improvements in their use.
I can be reached at 1606 Huntcliff Way, Gambrills, MD 21054.
Dona Sauerburger is an AER-certified orientation and mobility specialist with Volunteers for the Visually Handicapped in Silver Spring, Maryland.
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