Metropolitan Washington Orientation and Mobility Association Newsletter, January 1993
What Cues do Blind People Use to Recognize a Street in the Absence of a Curb?
by Dona Sauerburger, COMS
This article was based on my own experiences with 10 blind travelers when participating in a research project. A comprehensive report of the results from all 80 blind participants, including a list of cues they used, was published by the authors Dr. Billie Loise (Beezy) Bentzen and Janet Barlow in the following:
Bentzen, B.L. & Barlow, J.M. (1995). Impact of curb ramps on safety of persons who are blind. Journal of Visual Impairment and Blindness. Volume 89, No. 4, pp. 319-328.
Barlow, J. & Bentzen, B.L. (1995). Cues blind travelers use to detect streets. Technical report. Volpe National Transportation Systems Center, Federal Transit Administration.
Barlow, J. and Bentzen, B.(1994). Cues blind travelers use to detect streets. Technical Report. Cambridge, MA: U.S. Department of Transportation, Federal Transit Administration, Volpe National Transportation Systems Center.
I recently had the privilege of participating in a research project designed to find out if and how blind people can recognize where the street is when they approach it along a blended curb or ramp.
Eight O&M specialists across the country each asked 10 subjects to approach 10 intersections at which there was a ramp or blended curb, and to identify when their next step would be into the street.
The subjects were people who had little or no vision, and who felt they were capable of traveling independently in an unfamiliar area.
By talking with these experienced and skilled travelers, I learned worthwhile cues for recognizing a street in the absence of a curb.
More than 20 years ago, when I was trained as an O&M specialist, little or no significance was placed on the skills needed to recognize the street.
Almost without exception all streets had curbs which distinguished them from driveways and which made it easy to determine where the sidewalk ended.
Blended curbs were included in our O&M curriculum if we could find them; the technique (assuming you knew a blended curb was there) was to judge the distance by knowing the length of the block and listening to traffic (if there was any), and shoreline until the grass or building line disappeared.
Since that time, ramps have been installed at nearly every intersection throughout the country.
Many of these ramps are easy to detect because they are steep or abrupt, but others are not.
The travelers who participated in this research shared with me the strategies which they have developed and which are very effective, and which should be included among the O&M techniques and strategies that we teach to all our consumers.
Some of the strategies are familiar, such as listening to the traffic and checking for a shoreline.
Others, such as recognizing the open space of an intersection and listening for poles, were new to me.
Cues reported for detecting streets (in the order of frequency mentioned):
1. a tactual change such as:
the change in slope at the top or bottom of the ramp,
the change in surface texture of the street,
the seam line where the street pavement meets the sidewalk. Many were able to detect the slightest change, which alone did not indicate a street but which was sometimes enough in combination with the other cues.
2. sounds of traffic and pedestrians:
Parallel vehicles coming to a stop at the intersection, vehicles moving or idling on the perpendicular street, and pedestrians stopping to wait at the edge of the street or walking along the perpendicular sidewalk.
3. the disappearance of a shoreline (felt with cane) or a building line (usually heard, sometimes felt with a cane)
4. the sound or feel of an extended open area (that is, the area to the left or right along the perpendicular street).
Some people walked with a bouncing cane technique to hear its echo, and others could hear the open area using a regular touch or constant-contact technique.
Several reported hearing distant sounds from the side, such as trees and birds or construction, which are normally blocked by buildings and hedges in the middle of the block. One also reported feeling the air become more breezy as she stepped into the open area near the intersection.
5. poles (especially on the person's side that is opposite of the parallel street):
Several travelers pointed out that poles are usually found near curbs, so when they felt or heard a pole nearby, they became alert for other cues.
Detecting a pole nearby also helped them determine that the intersection was a street rather than a driveway.
6. the judgment of the length of a block, alerting the traveler to expect a street soon.
Some of the travelers were hesitant to report these tactics. When asked how he recognized the street, one subject said, "Well, you may think this is a little strange, but I can just feel that it is open here." Others were very conscious of their strategies; several purposefully pounded their canes when they felt a change in the slope, reporting they did so to identify by the sound if there was the wide open space that would indicate it was a street rather than a change in terrain or a driveway.
Travelers stressed that it is a combination of cues that typically enables them to identify the street. Each cue alone - traffic sounds, open spaces, or changes in the slopes and surface textures - were usually not enough to find the edge of the street, but in combination the cues could indicate the street.
Unfortunately, however, these strategies were not enough to consistently and dependably identify the streets.
When this study was done in cities where the ramps were all abrupt and the sidewalk flat and smooth, subjects easily identified almost every street.
At other sites however, including mine, even effective use of the above cues was not enough for every subject to identify every street. At one blended curb in my route, in spite of an abrupt end to the shoreline, a surface texture change, and a slight lip where the pavement overlapped the sidewalk, every traveler walked at least a few feet into the street before recognizing either the change in surface texture or the open area to the left. Five crossed without ever realizing there was an intersection.
Among the remaining approaches at the other intersections, there were 58 instances where subjects approached the streets along ramps without their feet touching any curb. Three ramps were at streets in residential areas, and 6 in busy urban areas. Unlike the blended curb which every one missed, these ramps were all detectable to at least some of the subjects, though some were very subtle.
Of these 58 ramp approaches, there were 6 instances where subjects went into the street and never knew they were crossing anything; two instances when subjects recognized it only when they were at least a third of the way across; and 3 instances when they went 4-8 steps into the street. In two other instances subjects crossed the streets thinking they were at driveways. Altogether, of the 58 times that people approached the street along the ramp, there were 13 instances when they went significantly into the street without realizing it.
In another 16 instances, people inadvertently took 1-3 steps into the street, and in four instances, travelers realized it was nearby but walked more than 8 steps into the street, looking for the edge. In total, among the 58 ramp approaches, there were 33 instances when people unintentionally put at least one foot into the street. In addition, subjects thought that driveways were streets 14 times.
The travelers varied somewhat in their ability to detect the streets. Two travelers went no further than a few steps into streets other than the blended curb, and another did as well except for crossing a street while thinking it was a driveway. Four others went significantly into one street in addition to the blended curb, and 3 travelers went into two or more streets.
Perhaps the reasons that the streets were sometimes not detectable are because
the cues must usually be used in combination with other cues, and
these strategies depend on consistency in the environment in order to be effective.
Combination of cues:
As an example of the unreliability of the combination of cues, one intersection had a very wide ramp with only a subtle change in slope at the top and bottom of the ramp (during a distance of about 4 feet it changed only 2-3 degrees). The perpendicular street was 4 lanes wide, and usually had heavy traffic moving with the green light. Nine of the 10 subjects located this street either before the edge, or within one or two steps after cautiously entering the street. All but one of these people reported that their main cues were the traffic sounds and the change in slope. Evidently in combination, these two cues were effective.
The subject who missed this street was very proficient at using cues to find streets (this was the only street which he failed to identify). However he happened to approach this street when there was no traffic moving on it, and the parallel traffic was moving. His only cue was the change in slope, which he said he felt but did not suspect it was a ramp. Thus when the cue of appropriate traffic sound was present, the combination of slope and traffic cues was effective, but the slope alone was not enough of a cue to identify the street.
Consistency of environment:
Lack of consistency in the environment caused some people to fail to identify streets. For example, several people ignored the ramp when the distance to the corner was much less than they expected. Another person recognized the ramp and stopped, but when his cane contacted a patch of grass in the street, he continued across the street assuming he was still on the sidewalk.
Another example of an inconsistent environment misleading the traveler occurred during my pilot study. The traveler, who was very proficient at identifying streets, failed to recognize a street even though its ramp was abrupt.
The reason was that she depended on the fact that normally intersections sound open (perpendicular streets are vacant), but this street had an overhead pass which blocked the sounds. By coincidence, although the street is moderately busy, there were no vehicles moving when she approached and entered the street.
A common problem?
I was surprised that several subjects were unaware that most curbs have been cut by or replaced with ramps, some of which are gradual or undetectable. During the experiment they seemed incredulous when they encountered several of the street edges which did not seem to have sufficient cues to identify the street. After they had traveled the route, when I asked them if they thought that a detectable surface texture would be helpful at curb cuts and blended curbs, they answered, "No, a curb would be better." One asked skeptically if this study was designed to recommend the installation of slopes at curb edges, apparently unaware that this is already commonplace. These people said they traveled to unfamiliar places occasionally but, as one pointed out, many of them nevertheless tend to travel in routine situations in familiar areas.
Implications for instruction
Our clients and students need to be aware that these intersections exist and in all likelihood will continue to become more prevalent. We need to expose them to these situations and strategies during training.
They need to realize, however, that even when using these strategies, they may inadvertently enter a street occasionally. Hopefully in the near future, city planners will either provide ramps that are more consistently detectable (that is, abrupt and steep enough), or install on the ramps tactile surface change that are standard (so they can be recognized as the edge of the street) and easily detectible with the foot or cane.*
Perhaps further research could help determine what kinds of approaches are dependably detected by blind travelers so we know how ramps might be designed to be recognizable as the street edge, and which edges need to be identified with tactual surface information.
* [LATER] It is unlikely that slopes will be designed to be detectible by the slope alone, because in order to be compliant with ADA regulations and be traversable by people in wheelchairs, the slope cannot be steeper than 1:12, and most people in the study were not able to recognize slopes less steep than 1:12. Therefore the only viable solution is to install detectable surfaces at the edges.
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