Excerpted From:
Public Rights-of-Way Access Advisory Committee
PART III: RECOMMENDED STANDARDS, SCOPING,
AND TECHNICAL PROVISIONS
X02.3.8.8 Audible Signs.
(A) General. Where there are audible signs, a visual equivalent shall be provided.
(B) Requirements for Remote Infrared Audible Sign (RIAS) Receivers. (1)
persons who are blind or who have print disabilities, basic speech messages shall
be frequency modulated at 25 kHz (+/- 10 percent deviation), and shall have an
infrared wavelength from 850 to 950 nanometer (nm). (2) Receiver shall produce a
12 decibel (dB) signal-plus-noise) ration with a kHz modulation tone at +/-
25 kHz deviation of the 25 kHz sub carrier at an optical power density of 26
Pico watts per square millimeter measured as the receiver photosensor aperture.
(3) The audio output from an internal speaker shall be at 75 dB(A) minimum at 18
inches with a maximum of 10 percent distortion. (4) The receiver photosensor
aperture shall be 80 degrees in acceptance angle. (5) The receiver shall be
designed for a high dynamic range and capable of operating in full-sun background
illumination. (6) Capture of the receiver by the stronger of two signals in the
receiver field of view requires a received power ratio on the order of 20dB for
negligible interference; adjacent transmitter frequency tolerance of 50 Hz to 100Hz
improves the intelligibility of interfering signals.
Advisory: Transit stations and platforms are routinely used by persons who are
blind. Tactile signs do not necessarily help persons who are blind to locate station
entrances and exits, fare gates, fare machines, stairs and escalators, platforms,
and other amenities, because tactile signs cannot be located consistently enough
for persons who are blind to find them efficiently. Remote infrared audible signs are
suggested as a wayfinding system because, like vision, they enable users to
scan the environment (using a personal receiver) and “read messages” from a
distance. They are able to provide directional and informational messages in a
way that enables persons who are blind to travel as independently as persons who
can read print signs.
Discussion: Remote infrared audible signs (RIAS) have been found to be a
particularly effective means to make wayfinding information accessible to
persons who are blind or who have print disabilities. Many transmission media
are potentially available for use in communicating wayfinding information to
people with print-reading disabilities (e.g., blindness, low vision, dyslexia, and
mental retardation). A key concern at this stage of technology development is the
possibility of blocking development of new technologies by inadvertently
limiting compliance to existing technologi8es.
Discussion: Currently there is a need to provide a uniform protocol for
communication of information by RIAS so that: (1) Users will not be required to
carry more that one receiver (one for each wayfinding application) to acquire
basic wayfinding information; (2) Users will be able to use the same receiver in
any location (within or between cities) so that the wayfinding environment is
“seamless”; (3) Manufacturers will be able to design basic functionality around a
single communication protocol. Additional enhancements would be permitted.
(4) Manufacturers and users will be able to take the protocol specifications to
national and international standards groups. Registering the protocol would help
provide a clear channel (free from interference from competing communication
technologies and interfering signals from other electronic devices and systems).
(5) Protocol must be coordinated with existing assistive listening device systems
to ensure simultaneous systems operations without disruption.