Quiet Cars and the Safety of Blind Pedestrians
by Dona Sauerburger, M.A., COMS
I am pleased and honored for this opportunity to participate with NHTSA in a meeting on such an important topic. As an orientation and mobility specialist, I have been teaching people who are blind or visually impaired to travel independently for more than 38 years.
This paper will explain that
the issue of quiet cars is a complex one, requiring complex research involving blind subjects performing realistic street-crossing tasks to address it, and
quiet cars present both an extreme case scenario as well as the tip of the iceberg of the multitude of problems that exist for people who rely on hearing to cross streets.
Traditionally, blind people use the sounds of traffic to successfully determine everything needed in order to cross streets. When our profession was developed in the 1950's with soldiers blinded from World War II, these vehicular sounds were more than sufficient for blind pedestrians to perceive acoustic walls and patterns that revealed the intersection geometry (such as width of the street and the angle and number of legs); the traffic control and appropriate time to cross; the alignment and the position when preparing to cross and, during the crossing, enabled them to maintain alignment and avoid vehicles turning into their path.
By 1969, when I started teaching blind people to cross streets, traffic sounds were still sufficient to enable blind people to cross streets safely.
The average sound level for passenger cars at that time was about 90 dB (Wiener, 1997).
However,* the U.S. Federal-Aid Highway Act of 1970 and the Noise Control Act of
directed the Federal Highway Administration and the Environmental
Protection Agency to develop standards for mitigating traffic
noise. The Noise Control Act of 1972 authorized the Environmental
Protection Agency to develop noise emission standards for motor and
engine powered equipment, including automobiles. To date, no federal
noise limits exist for cars, but currently in the U.S., automobile
manufacturers design cars to meet the European noise limit of 78 dBA or
less. (Federal Highway Administration, 1995,
Ken Feith, personal communication 2008).
During the ensuing years, acoustic information from vehicles has been decreasing, while at the same time intersection geometry and traffic control have become increasingly complex and challenging. Gradually it has come to the point that there are now many situations where the sound of traffic is no longer sufficient to make all the determinations and judgments needed to cross streets safely.
For example, at streets with no traffic control, there are some situations where even people with the keenest hearing cannot hear most cars until they are too close. In a study by Western Michigan University (Wall Emerson, R. and Sauerburger, D., in press) at quiet, two-lane residential streets, blind people listened for approaching vehicles. At some sites, all vehicles could be heard far enough away to be assured it was clear to cross when quiet but at other situations, even when it was quiet, vehicles could not all be heard with a sufficient safety margin.
At signalized intersections, it is also sometimes impossible to hear the traffic sounds needed to perform street-crossing tasks. Sometimes this is because there is insufficient traffic, and sometimes it is because the traffic that must be heard is too far away and/or is masked by the sound of nearby traffic or other sounds.
Being able to recognize when drivers yield to the blind pedestrian has also become problematic. In a study by the Federal Highway Administration (Inman, Davis and Sauerburger, 2005), blind subjects were able to hear yielding vehicles in both lanes at a two-lane roundabout an average of only 19% of the time, and 14% of the instances when they thought they heard vehicles yielding in both lanes, they were wrong.
This increasing problem of insufficient traffic sound has reached the extreme with the onset of quiet cars, including hybrid and electric cars. Our professional organization, the Orientation and Mobility Division of AER (the Association for Education and Rehabilitation of the Blind and Visually Impaired), has been concerned about the problem of quiet cars since 1996. That year, AER passed a resolution urging research to determine alternative technologies and techniques to enable blind people to accomplish the street-crossing tasks in situations where not all vehicles are audible either at a distance or nearby.
In 2000 AER passed another resolution urging that research be undertaken, this time with the specific goal of determining the minimum amount and nature of acoustic information necessary to enable blind pedestrians to accomplish the street-crossing tasks. This resolution urged the National Highway Transportation Safety Administration to hold vehicle manufacturers accountable for meeting minimum acoustic information standards determined to be necessary to assure the life safety of pedestrians who are blind and visually impaired.
In 2004 we were back at it again urging research, but this time with a broader perspective. This resolution
(1) recognized that blind people aren't the only ones who use the sound of vehicles to navigate streets and parking lots safely, and
(2) reflected the fact that the ability to hear vehicles is likely to continue to decrease in view of efforts to reduce vehicular tire and road noise.
AER therefore urged that research be done to:
evaluate the effect of quiet vehicles on pedestrian safety, especially the effect on children, pedestrians who are elderly, and pedestrians who are blind or who have low vision, and
determine techniques for providing information that is equivalent to the acoustic cues that are currently provided by vehicle engines, that will enable blind pedestrians to cross streets;
evaluate the broader issues of environmental access and wayfinding that large numbers of quiet vehicles would present to the abilities of blind pedestrians to accomplish street-crossing tasks; and to
develop techniques and technologies to address problems found.
Finally, the resolution:
urged NHTSA, FHWA, the Access Board and Transport Canada to promptly implement results of this research to provide acoustic safety and orientation information (information which is not provided by quiet vehicles) to all pedestrians, including those with visual impairments.
(1) All pedestrians need to hear the cars:
This AER resolution reflected research by Tamara Bond and Randolph Easton at Boston College that indicated that the sound of vehicles is used by all pedestrians, such that eliminating or reducing vehicular sound level would negatively affect all pedestrians. Their study was done at a two-lane street where students were asked to indicate when they felt it was safe to guide a young child across the street, and when it was no longer safe. A "risky decision" was one where the participant still felt it was safe to cross when, in fact, a car was too close (it would have reached them before their crossing was done). When participants had to use vision only, they made about 10% more risky decisions than they did when they were able to hear the vehicles as well as see them.
(2) All traffic sounds are getting quieter
The AER resolution also reflected concern about the fact that there are efforts to reduce all sounds related to moving traffic, making reliance on these sounds for street-crossing decisions increasingly tenuous. The U.S. Federal-Aid Highway Act of 1970 mandated the Federal Highway Administration to develop noise standards for mitigating highway traffic noise (Federal Highway Administration, 1995). Part of these efforts to reduce the sound level of traffic included developing quieter tires and pavement. For example, in 2001, Purdue's Institute for Safe, Quiet, and Durable Highways worked with the U.S. Department of Transportation to help tire manufactures design tires that make less noise (Wiebusch, 2001). In 2002 a $34 million Quiet Pavement Pilot Program was launched in Arizona to resurface highways with an asphalt rubber friction course overlay that can reduce the sound level of moving vehicles 3-5 dB(A) compared to traditional asphalt surfaces, and 6-12 dB(A) compared to concrete surfaces (Manuel, 2002). This trend to quieter pavement and tires will make it even more difficult for pedestrians to hear the cars, increasing risky decisions and difficulties accomplishing safe street-crossing tasks.
Pedestrians, including those who are blind, cannot always detect and avoid vehicles, especially as the cars become more and more quiet, and they also cannot rely on drivers to watch for them and avoid collisions by yielding. Research shows that in the U.S., even when pedestrians with white canes are clearly visible and the crosswalk and even pedestrian laws are clearly marked, drivers do not reliably yield to them (Geruschat, D, and Hassan, S. 2005, Inman, Davis & Sauerburger, 2005). As previously noted, even when drivers do yield to blind pedestrians, the pedestrian cannot always hear that a car has stopped.
When pedestrians are not readily visible to the drivers, for example when drivers are backing out of parking spaces, drivers are even less likely to yield. I personally know of at least a half dozen people who have been knocked over by drivers who were looking to the left while turning right-on-red or turning right from a driveway into a busy street - the drivers each claimed that they never saw the pedestrian. Therefore it is essential that pedestrians be able to detect vehicles to avoid collision. For example, there is a well-recognized need for providing a sound for trucks that are backing up and for other vehicles from which drivers may have limited visibility for pedestrians, especially children and people in wheelchairs.
So we have an urgent problem, and the problem is both broad and complex. Having cars make a minimum noise may not be enough to address all the problems that are presented by insufficient traffic sounds, and we may need solutions that provide alternative strategies for getting the information needed. Increasing the sound of cars is critical, but it is only one of a range of possible solutions for some of the problems caused by insufficient vehicle sound.
Information as to the phase of traffic signal, which traditionally had been obtained from traffic sounds that may no longer be there, can be provided with well-designed and -installed alternative pedestrian signals.
At traffic signals, the risk of being hit by turning cars which cannot be heard can be reduced with lead pedestrian intervals.
Alignment information that is necessary to avoid walking into the path of speeding vehicles in the street adjacent to the crosswalk - information which can no longer always be obtained by hearing the traffic - might be provided with tactile strips and cues.
Gap-in-traffic information which is necessary to cross streets where there is no traffic control - information which can no longer be obtained auditorially at situations such as roundabouts where the sound of approaching vehicles is masked by the sound of nearby traffic - can be obtained by installing traffic and pedestrian signals.
At streets with no traffic control where hills and bends make it impossible to hear cars from far enough away to know if it is clear to cross, the risk of crossing and the need to hear cars at a distance can be reduced by shortening the length of the crossing and slowing the traffic, for example with the installation of bulbouts and refuge islands.
However there are situations for which there is no solution that can substitute for the audible sound of the vehicle itself. This is true not just for blind people, but for all pedestrians. And lest we think that being unable to detect cars moving in parking lots is not a serious matter, I will relate to you what happened to Maxine Deplane in a parking lot in the Maryland suburban community where I live. Maxine worked at my travel agency, and had normal vision and hearing and a warm smile whenever she greeted me. As she walked from her car to her grocery store, an elderly driver knocked Maxine down and then drove over her without realizing she was there. Maxine died a few hours later, after saying farewell to her husband who was summoned to the parking lot.
We therefore need research to:
determine the scope of problem (in what situations does the insufficient or lack of sounds from vehicles cause a problem?);
develop solutions to these problems, and determine the effectiveness of those solutions (these solutions may require more than just having the vehicles make a sound);
determine what problems will be solved by simply enhancing the sound of cars, and what kind of sound will address those problems adequately.
Western Michigan University has been and continues to be actively involved in researching hybrid cars and their effect on the safety of street-crossing decisions of blind people. An initial study verified suspicions that hybrids have a tighter correlation between speed and sound than vehicles with internal combustion. That is, as they go slower, hybrid vehicles get quieter than others, although the difference is most noticeable only when they are going slower than about 15 mph.
The importance of using actual blind people in these studies is illustrated by the fact that WMU found that when vehicles approach subjects at 15-20 mph, even though the sound level of the Toyota hybrids was measured as higher than that of the Honda hybrids, the Toyotas were much more difficult to detect. Hondas were detected 5-6 seconds away but Toyotas going at the same speed were not detected until they were less than 2 seconds away.
This would seem to indicate that it is not a simple issue, solved by sound level alone. It may involve sound frequency or other sound features, and we need to determine what those features might be. WMU plans to do more research with hybrids at intersections with signals this August. The tasks needed to cross streets at signals are quite different from those needed to cross where there is no traffic control, and their studies will examine these tasks in view of traffic consisting of hybrid cars.
In conclusion, we urge the support of immediate and comprehensive research to understand the effect of quiet cars on the street-crossing tasks and safety of all pedestrians, especially those who are blind; study the broader issue of street-crossing tasks, safety, and strategies used by blind people in a world where diminishing traffic sounds are mandated by government regulations; and develop solutions and test their effectiveness.
* This is altered from the original paper to correct the erroneous statement that "in 1972, regulations required that the sound of passenger vehicles be no more than 78 dB." The U.S. has studied and considered sound restrictions but never established regulations regarding passenger vehicles.
Bond, T, and Easton, R. (in press). The relative contributions of audition and vision to pedestrian street crossing judgments. Journal of Visual Impairment and Blindness, AFB Press
Federal Highway Administration (1995). "Highway Traffic Noise Analysis and Abatement Policy and Guidance" FHWY Office of Environment and Planning, Noise and Air Quality Branch, Washington, DC
Geruschat, Duane R. And Hassan, Shirin E. (2005) Driver Behavior in Yielding to Sighted and Blind Pedestrians at Roundabouts. Journal of Visual Impairment and Blindness, Volume 99:, No. 5, 286-302.
Inman, V.W., Davis, G.W., and Sauerburger, D (2005) Pedestrian Access to Roundabouts: Assessment of Motorist Yielding to Visually Impaired Pedestrians and Potential Treatments to Improve Access. Washington, D.C.: Federal Highway Administration, FHWA-HRT-05-080.
Manuel, John (2005). Clamoring for Quiet: New Ways to Mitigate Noise" Environmental Health Perspectives, Vol. 113, No. 1
Wall Emerson, R. & Sauerburger, D (in press). Detecting approaching vehicles at streets with no traffic control. Journal of Visual Impairment and Blindness, AFB Press
Wiebusch, B. (2001) "Engineers Tread on Quiet Tires." Design News, December 3, 2001
Wiener, W. R. (1997). Audition for the visually impaired traveler. In Welsh, R., Wiener, W. R., & Blasch B. B. (eds.) Foundations of Orientation and Mobility, Second Edition. AFB Press: New York, NY
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