The Braille Monitor                                                                                       January 2003

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Comments to the Access Board on Detectable Warnings

by Michael Freeman

From the Editor: Mike Freeman is one of the leaders of the NFB of Washington. He is an experienced cane user with definite views about detectable warnings of all kinds. Here is the comment he submitted to the Architectural and Transportation Barriers Compliance Board (ATBCB), known more familiarly as the Access Board. It is representative of the thinking of many of the Federationists who filed comments. This is what Mike said:

Mike Freeman
Mike Freeman

Michael Freeman

Vancouver, WashingtonSeptember 24, 2002

Scott Windley

Office of Technical and Information Services

Architectural and Transportation Barriers Compliance Board

Washington, D.C.

Dear Sir:

I am writing to comment on the draft guidelines for accessible public rights of way recently published by the Architectural and Transportation Barriers Compliance Board (ATBCB) as Docket Number 02-1, RIN 3014-AA26 to be codified at 36 CFR Parts 1190 and 1191 as published in the Federal Register of June 17, 2002. I am blind.

In general I am opposed to the guidelines for Accessible Pedestrian Signals (APSs). They are largely unnecessary, they will have unacceptable adverse consequences, and they will require far more modification of the environment than is needed. I am also opposed to the guidelines on detectable warnings. In most situations these are not needed, and, where they are appropriate, the guidelines specify what is, in my opinion, the wrong type of detectable warning.

I shall expand upon these comments below. Before I do so, however, some preliminary remarks are in order: (1) I believe that, in formulating the guidelines respecting accessible pedestrian signals and detectable warnings, ATBCB should adopt the philosophy that only those modifications to the environment deemed absolutely necessary for the average blind person with some travel skills to function should be imposed and that guidelines should be formulated under the assumption that blind people possess decent travel skills rather than under the assumption that they have minimal travel skills and require a great deal of assistance in crossing streets and other thoroughfares. I, like most blind people, travel in most situations with perfect ease and safety without special environmental adaptations.

(2) I believe that most of the problems proponents of accessible pedestrian signals allege are not so much the result of lack of access to pedestrian signals as a result of a shift in the paradigm of design criteria for public rights of way. Several traffic engineers have told me that public rights of way are increasingly designed to facilitate the flow of vehicular traffic rather than to facilitate pedestrian access. In my view the supposed need for accessible pedestrian signaling devices would largely be obviated and the environment would be made safer for all pedestrians (blind and sighted alike) were the guidelines to force a shift in the design paradigm back to a pedestrian-oriented model.

Advocacy of audible pedestrian signals is predicated upon the analogy that aural cues are to the blind what visual cues are to the sighted. There is a measure of truth in this analogy. However, when closely examined in the context of APSs, the analogy breaks down. Slavishly adhering to it could have severe, if not fatal, consequences.

The sighted can physically pay attention to or ignore visual pedestrian signals when assessing vehicular traffic to determine when it is safe to cross streets, roads, roundabouts, and the like. This is in sharp contrast to the predicament of the blind when encountering APSs, which use audible cues.

Sound, being a pressure wave, is all-pervasive; sounds are superimposed upon each other. The brain separates and classifies sounds by analysis rather than by physical action (eye movement in the case of vision). Thus persistent sounds such as the periodic tones for APSs specified in Section 1106.2.3.1 often mask other sounds such as traffic flow which are of vital importance when assessing crossing safety. Add to this the multiplicity of locator tones as specified in Section 1106.3.2.1, and the resulting cacophony will be extremely distracting to blind pedestrians and could spell disaster for them if they miss the sound of an approaching vehicle while attempting to sort out the plethora of tones generated by the APS.

In my view mandating any APSs with audible indicators is, therefore, unacceptable and inadvisable. In my view Accessible Pedestrian Signals should be mandated only for complex street geometry, complex traffic flow, or complex signalization. In these situations, however, under no circumstances should audible indicators be mandated or used. They are too distracting (hence, dangerous). Instead, vibrotactile APS systems should be employed.

Especially in urban environments sound reflects from a multitude of objects in the vicinity of street crossings, creating manifold echoes, making accurate assessment of audible APS location confusing at best and impossible at worst. Since the location of actuators for APSs is specified at Section 1106.2.1, I can see no reason whatsoever for provision of locator tones. If the guidelines are followed, the APS actuators will be in relatively standard positions with respect to crosswalks.

Moreover (the guidelines are unclear on this point), conventional intersections could have between four and eight emitters of locator tones. As I said above, such a plethora of tones would be extremely distracting for a blind person who, as I often do, listens to several traffic cycles to assess traffic flow, the signal pattern, and how well vehicular traffic is obeying the signals. This noise is unhelpful at best and could be tragic at worst. Mandating locator tones should be eliminated from the guidelines.

Under most circumstances I see no need for detectable warnings (Section 1108). A blind person using either a long cane or a guide dog can usually determine where the boundary between a sidewalk and street lies. Normally curbs and curb cuts with ramps are easily detected. It is becoming increasingly common, however, for sidewalk/street boundaries to be designed to blend smoothly into each other and to be so flat as to be virtually undetectable by nonvisual means. It therefore makes sense under these restricted circumstances to have some sort of tactile detectable warning. The background material for these guidelines stated that one organization of the blind suggested that detectable warnings should be used whenever the slope leading from a sidewalk to a street had a gradient less than one to fifteen. This proposal makes eminent sense to me.

I therefore advocate that the guidelines specify that detectable warnings be used under these conditions and under no others. I do not, however, favor that detectable warnings be in the form of truncated domes as specified in Section 1108.1. It seems to me that a better solution would be to specify a general roughened surface in the zone, which would constitute the detectable warning, or a warning zone consisting of alternating strips of contrasting surface textures. Such a warning system would not interfere with operation of wheeled vehicles and would not constitute a tripping hazard. It might even help with traction.

In summary, APSs should be used only under conditions of complex traffic flow or signalization and should employ vibrotactile rather than audible indicators. Likewise detectable warnings should be used only when the transition of sidewalks to streets is undetectable using a cane or guide dog. As I stated in my introductory remarks, the operating principle should be to change the environment as little as possible consistent with pedestrian safety.

I appreciate the opportunity to contribute my views and thoughts on the access guidelines for public rights-of-way and thank you for your attention.


Michael Freeman

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