Several have written seeking more information about the report
commissioned by the U.S. Access Board on accessible traffic signals for
blind travelers. It is included below.
if you want a copy in another format, "Accessible Pedestrian Signals,"
Publication A-37, is available without charge from the US Access Board by
calling its toll-free line at 1/800/872-2253 (press `1' and follow
ordering instructions).
The American Council of the Blind, http://www.acb.org, has many documents
on pedestrian safety on its web site, if further information is sought.
I should note that Billie Louise Bentzen conducted much of the
federally-funded research on detectable warnings in the 1970s and 1980s.
This research was used as a basis for developing the guidelines
supplementing the Americans with Disabilities Act.
kelly
ACCESSIBLE PEDESTRIAN SIGNALS
Billie Louise Bentzen, Ph.D.
Lee S. Tabor, AIA
Accessible Design for the Blind
P.O. Box 1212
Berlin, Massachusetts 01503 USA
978-838-2307 voice/fax
[log in to unmask]
4 August 1998
Work performed in support
of the U.S. Access Board
under Contract No.PD-97-0772
_________________________________________________________________
TABLE OF CONTENTS
Accessible Pedestrian Signals 2
Information Requirements at Intersections 3
Accessible Traffic Signal Technologies 5
Characteristics of Accessible Pedestrian Signals 8
Determining When to Install Accessible Pedestrian Signals 13
Specifying Accessible Pedestrian Signals 15
Installing Accessible Pedestrian Signals 16
Pedestrian Detection Technology 17
Matrix: APS Functional Characteristics 18
APS Product Sources 20
Sources of Information 21
References 23
ACCESSIBLE PEDESTRIAN SIGNALS
Introduction
The Transportation Equity Act for the 21st Century--TEA-21, the
successor to ISTEA--directs that pedestrian safety considerations,
including the installation of audible traffic signals, where
appropriate, be included in new transportation plans and projects
[Sec. 1202(g)(2)]. The bill was signed into law by the President on
June 9, 1998.
Accessibility
The Americans with Disabilities Act (ADA) requires access to the
public right-of-way for people with disabilities. Access to traffic
and signal information is an important feature of accessible sidewalks
and street crossings for pedestrians who have vision impairments.
While most intersections pose little difficulty for independent
travelers who are blind or have low vision, there are some situations
in which the information provided by an accessible pedestrian signal
is necessary for independent and safe crossing.
How Persons Who Are Blind Cross Streets
Techniques and cues used in crossing streets are diverse and vary by
location and individual. Many visually impaired pedestrians have
trained with an Orientation and Mobility Specialist who has an
undergraduate or graduate degree in teaching travel skills to persons
who have visual impairments. In the most common technique utilized for
crossing at signalized intersections, pedestrians who are blind begin
to cross the street when there is a surge of traffic parallel to their
direction of travel.
Vehicular sounds are often sufficient to determine the onset of the
WALK interval and the direction of the crosswalk. However, there are
some intersection geometries, acoustic conditions, and traffic control
systems which make it very difficult for persons who are visually
impaired to obtain the cues necessary to cross streets independently
and safely. Accessible traffic signal technologies can be helpful to
pedestrians in these situations.
Value of Accessible Pedestrian Signals
Accessible pedestrian signals (APS) that provide audible and/or
vibrotactile information coinciding with visual pedestrian signals let
pedestrians who are blind know precisely when the WALK interval
begins. This information is useful in analyzing an intersection and
preparing to cross. Pedestrians who know when the crossing interval
begins will be able to start a crossing before turning cars enter the
intersection and can complete a crossing with less delay. Audible
signals can also provide directional guidance, which is particularly
useful at non-perpendicular intersections and at wide multi-lane
crossings.
The redundant information conveyed by audible pedestrian signals
increases the attention of all pedestrians to turning traffic and may
contribute to a reduction in pedestrian-vehicular conflicts and
crashes at signalized intersections (R. Van Houten, Malenfant, J. Van
Houten & Retting, 1997). It is widely believed in many European
countries, where the use of audible pedestrian signals has been more
extensive than in the U.S., that the presence of audible pedestrian
signals increases the speed at which most pedestrians initiate their
crossings, thereby decreasing the necessary length of the pedestrian
interval. Audible pedestrian signals may also increase the safety of
persons with cognitive disabilities.
History of APS in the U.S.
Federal and model code accessibility standards in the U.S. do not yet
include scoping or technical provisions for APS or other means of
communicating visible signal information to pedestrians who have
vision impairments. Regulators have been reluctant to standardize on
any current device or system until more research and development is
done on applications of emerging intelligent transportation systems
and related communications technologies.
Although audible crossing indicators have been available for over 25
years, they have not been well received by traffic planners in the
United States. This is probably attributable to two factors: one is
noise pollution and consequent community opposition; the other is
disagreement among blind people on the need for and effectiveness of
audible pedestrian signals.
However, changes in traffic control and signaling design and practice
today have greatly disadvantaged blind pedestrians who wish to travel
independently. The Department of Justice has recognized that APS may
be necessary at some locations in order to provide access for a
pedestrian who is blind to the "program" of pedestrian circulation
provided by a jurisdiction.
INFORMATION REQUIREMENTS AT INTERSECTIONS
Introduction
Travel along regular routes and on regular schedules is routine for
most blind pedestrians. However, independent travel to unfamiliar
destinations is a more complex undertaking, requiring access to
information on the pedestrian and street environment at decision
points along the route. Most blind pedestrians will be able to cross
streets safely and independently if they have access to the same range
of information available to pedestrians who are fully sighted.
Detecting the Street
The first information needed by the pedestrian who is blind is "Have I
arrived at a street?" Before the advent of curb ramps, depressed
corners, and built-up intersections, the presence of a curb was an
unambiguous cue to the sidewalk/street edge. In the absence of a curb,
even experienced blind pedestrians using an unfamiliar intersection
with a curb ramp have a high probability of entering the street before
they are aware of leaving the sidewalk (Bentzen & Barlow, 1995;
Hauger, Rigby, Safewright, & McAuley, 1996). Blind travelers whose
path of travel coincides with a single curb ramp at the apex of a
corner--a diagonal curb ramp--may inadvertently enter the stream of
parallel traffic (Hauger et al., 1996) without being aware of the
sidewalk/street boundary.
In some countries (including Japan, England, and Australia), surfaces,
which are highly detectable under foot or detectable by the use of a
long cane, provide definitive information to pedestrians who are blind
that they have arrived at a curb ramp. The International Standards
Organization (ISO) is proposing a standardized truncated dome surface
for use as a warning of the sidewalk/street boundary ahead. It is
similar to the detectable warning surface specified in the ADA
Accessibility Guidelines (ADAAG) 4.29.2 for use on the edges of
transit platforms.
Identifying the Street
The next information needed for decision-making at unfamiliar
intersections is: "Which street is this?" This information is seldom
provided in any accessible format. Pedestrians who are visually
impaired develop a mental map and keep track of where they are within
that map, usually by counting blocks and street crossings. Where
necessary--and available--assistance may be sought from other
pedestrians.
Analyzing Intersection Geometry
The next information needed is: "What is the geometry of this
intersection?" Important pieces of information which are obvious to
pedestrians having full vision, but which may not be possible for
pedestrians who are blind to determine by listening to traffic
patterns, are the following:
o Is my destination curb straight in front of me, or must I angle to
the left or right to reach it?
o How many streets intersect here?
o How wide is this street?
o Should I expect to encounter any islands or medians as I cross this
street?
o Am I standing within the crosswalk?
Incorrect or missing information for any of these questions may result
in missing the destination curb or median.
Analyzing the Traffic Control System
Next, pedestrians need to identify the type of traffic control system
at this intersection:
o Is this a signalized intersection?
o Do I need to push a button to actuate the walk interval? If so,
where is the button?
o Is the button close enough to the crosswalk that I will have time to
position myself correctly at the crosswalk, facing my destination
curb, before the onset of the walk interval?
o Which button controls the walk interval for the street I want to
cross?
o Does it stop traffic on one street, or all traffic?
o Do cars still turn during the walk interval?
o Is there a second button I must push that is on a median?
o Will there be a surge of parallel traffic telling me the walk
interval has begun?
o Will I be able to hear it over other, concurrent traffic sounds?
Missing information for any of these questions may result in failing
to use pedestrian push buttons and crossing at times other than the
pedestrian phase. In research conducted for the San Diego Association
of Governments (1988), blind pedestrians had significant difficulties
finding the push button and realigning at the curb for crossing. On
50% of trials in research conducted in San Francisco (Crandall,
Bentzen and Myers, 1998), blind pedestrians crossing at four
unfamiliar fixed timed signalized intersections that did not have APS
were not able to obtain sufficient information from traffic sounds and
other cues to identify whether an intersection was signalized or had
stop signs.
Identifying the Crossing Interval
After determining the geometry of the intersection and aligning so
they are facing towards the destination curb--and having determined
that an intersection is signalized and pushing a button, where
necessary--pedestrians who are blind need to know: "When does the WALK
interval begin?" In the absence of APS, pedestrians who are blind use
the surge of traffic on the street beside them (parallel traffic) to
indicate that they have the WALK interval. On 34% of trials in
research cited above (Crandall et al. 1998), participants who were
blind did not have sufficient information to begin their crossings
during the WALK interval and initiated a crossing out of phase.
Too little traffic may be as information-poor as too much. Sometimes
there is no surge of parallel traffic, such as at intersections where
all traffic stops during the pedestrian phase, mid-block crosswalks,
and intersections where--or when--there is little or no traffic on the
parallel street. Useful rush hour traffic noises may be absent in the
evening or even at lunch hour. Sometimes streets are so wide or in
such noisy environments that the surge of parallel traffic cannot be
heard. Where there is split phase timing to permit left turns, the
surge of left turning cars may be mistaken as indicating the onset of
the WALK interval and blind pedestrians may cross into the paths of
left turning vehicles.
Starting the Crossing
Being able to start a crossing soon after the onset of the parallel
traffic surge requires fast decision-making. And distinguishing
between a surge of parallel traffic indicating the onset of the WALK
interval and a single car turning right on red after stopping requires
good listening and good spatial thinking. A majority of persons who
are visually impaired are over the age of 65, by which time they may
be experiencing age-related hearing loss and delayed reaction times.
They often require a few seconds to be certain of the parallel traffic
surge, and therefore may not start soon enough to clear the street
within the clearance interval. Pedestrians who have low vision may use
visual cues to identify and avoid vehicles within close range.
However, pedestrians who are blind must proceed more cautiously. This
often means ceding the right of way to a vehicle stream that, once
established, may not offer a pedestrian gap until another cycle has
been called.
Maintaining Crossing Alignment
Once the pedestrian who is blind has begun to cross the street, the
next question is: "Am I headed straight towards my destination curb?"
Traffic going straight ahead on the parallel street provides helpful
auditory guidance to many persons if it is present. However, abundant
turning traffic makes it difficult to hear traffic going straight, and
difficult to use its sound to maintain a straight line of travel. When
traffic is absent, blind pedestrians have no guidance from vehicular
sounds either for determining the onset of the WALK interval or to
maintain alignment while crossing the street. The wider the street,
the more severe the consequences of even slight veers from the
crosswalk area.
ACCESSIBLE TRAFFIC SIGNAL TECHNOLOGIES
Types of Signals Providing WALK and DON'T WALK Information
A number of technologies exist which provide WALK and DON'T WALK
information. These APS provide information that is audible,
vibrotactile, or both.
The matrix entitled "Accessible Pedestrian Signals: Product Functional
Characteristics" shows the functional characteristics of each product.
Manufacturer information is given on the page following the matrix.
All products produce a sound, vibration, or both, during the walk
interval. Beyond this, there is great variation in the functional
characteristics of different products, with some providing information
throughout the signal cycle. A few devices have audio output that
varies, by message or repeat frequency, as the pedestrian cycle
changes from WALK to DON'T START to DON'T WALK.
Currently available products are of three design types, categorized by
the location from which the audible or vibrotactile cue is given:
o speakers mounted in, on or near the visible ped-head;
o transmitters mounted in or on ped-heads, and
o sound generator and vibrating hardware which are integrated into the
push button at or near the curb.
Like visible pedestrian signals, devices that use audible speakers
and/or vibrating hardware will provide cues at both ends of a crossing
when the pedestrian interval is actuated. Transmitter/receiver systems
respond to individual use, and so will 'read' only the transmitter
that is being scanned.
Speakers Mounted In, On, or Near Ped-heads
Products that have speakers mounted in, on, or near ped-heads emit a
sound such as a bell, buzz, tone or birdcall (typically cuckoo and
chirp) during the WALK interval. (Examples: IDC, Mallory, Novax, STN
Atlas, and Wilcox) If such a signal is loud enough to be heard across
the street, if the tone is highly localizable, and if the speaker is
carefully oriented, the signal also functions as an audible beacon,
providing guidance for going straight across the street.
If the tone is not highly localizable or the speaker is not carefully
oriented, such a signal may give ambiguous information about which
street has the WALK interval, and may give false information about the
direction of the crosswalk. A tone that is loud enough to be heard
across the street may be perceived as obnoxious by other persons in
the vicinity and may mask traffic sounds which provide critical safety
information.
Tones that alternate from one side of the crossing to the other have
been shown to enable blind pedestrians to cross more directly and
quickly. They are also less likely to mask traffic sounds.
A figure shows a rectangular box, perforated on one side, with rounded
corners. It has a hinged attachment to the top of the ped-head so it
could be angled somewhat up or down. This equipment is manufactured by
IDC.
Transmitters at the Ped-head
Infrared or LED transmitters located at the ped-head can transmit a
speech message to hand-held receivers (Examples: Talking Signs,
Relume). Messages may identify the location and direction of travel of
the pedestrian, give the name of the street to be crossed, and provide
real time information about WALK and DON'T WALK intervals. It is
essential that the information regarding the light cycle be received
only when the user is standing at the crosswalk with the receiver
aimed at the transmitter on the opposite curb, or the information can
be ambiguous.
For example, the Talking Signs system installed at several
intersections in San Francisco transmits a message that includes the
name of the street on which the pedestrian is traveling, the direction
of travel, the block the pedestrian is on, and the name of the
intersecting street he/she is approaching. Standing within the limits
of the crosswalk at the intersection, the pedestrian can pick up a
repeating message stating the name of the street and the status of the
cycle. For example, "Wait--Grove Street," or "Walk sign--Grove
Street." To ensure safety, a pedestrian must receive the same message
for the same traffic condition at every crossing equipped with
transmitters.
A transmitted system can convey more--and more precise--information
about individual intersections than any other APS. It can be adapted
for vibrotactile use by deaf-blind pedestrians and may be engineered
for output in other languages. It is excellent for atypical
intersections where there are more than four crosswalks, and when
direct signals, such as tones, may overlap and therefore be unclear or
misleading. There is no noise pollution with such a system--the
information is only received by individuals when they desire it--but
it does not benefit other pedestrians at the same crossing. Such
systems require users to obtain, carry, maintain and use receivers,
which raises issues of distribution and availability to non-residents.
However, the increasing use of personal pagers, cellular telephones,
and other mobile digital communications devices suggests that personal
telecommunications equipment will be commonplace in the near future.
Figure: A Bird's Eye View of Talking Signs(reg. tm) Infrared
Transmitter System for Intersections. Pedestrian Hears Voice Message
from Hand-held Receiver
The above illustration shows how the Talking Signs infrared
transmitter delivers messages to the pedestrian who is carrying a
receiver.
Wide beam tells:
o Direction of travel - "traveling east"
o Present location - "on zero hundred block of Larkin"
o Intersecting street - "towards Grove Street"
Narrow beam tells:
o Crossing condition and intersecting street - "wait--Grove Street"
"walk sign--Grove Street"
o Safe crosswalk zone
This figure is a diagram of the angles of transmission for the Talking
Signs system as it is used at intersections. It shows the intersection
of Larkin Street and Grove Street. Square boxes on the northeast and
northwest corners of the intersection represent the transmitters that
would be placed on the ped-heads at those corners. Each box has a
narrow cone coming out one side and a wide cone coming out the other
side. Narrow transmission cones send messages in both directions
across Grove Street about the crossing condition and the name of the
street, for example, "Wait--Grove Street" or "Walk sign--Grove
Street." Wider cones send messages away from Grove Street, along
Larkin Street carrying information about location, for example,
"Traveling east on zero hundred block of Larkin towards Grove Street."
Sound Generator and Vibrating Hardware Integrated into the Push Button
A third type of APS, which has been standard in Australia and Sweden
for many years, is fully integrated into the pedestrian push button
assembly (Examples: Campbell/Panich, Georgetown, Polara Engineering,
Prisma Teknik). Some provide vibratory information only; others
augment vibrotactile hardware with a quiet, slowly repeating, tick,
click, or tone to identify the location of the push button during the
DON'T WALK and pedestrian clearance intervals, and a faster tick,
click, or tone to identify the WALK interval.
Audible push button locating signals are heard only from the near
vicinity of the push button. They let pedestrians know that the
intersection is one that requires pedestrian actuation to call a WALK
interval. The tick/click/tone also signals where to find the push
button. The locator tone coming from the push button assembly during
the DON'T WALK and clearance intervals becomes a louder and faster
tone during the WALK interval. Tones coming from the push button are
often found to be less objectionable in quiet settings than the tones
coming from the ped-head.
Most APS devices that are integrated into the push button incorporate
a raised (tactile) directional arrow. Some manufacturers offer options
for additional tactile information that describes street crossing and
traffic signal characteristics in braille or raised diagrams.
Vibrating devices may be particularly applicable at intersections with
medians, where a full crossing requires pedestrians to wait at the
median for a subsequent cycle. Since the sounds of multiple audible
signals may overlap in such settings, they are not recommended because
of the possibility of conveying conflicting information. Vibrotactile
signals may also be more suitable at intersections with channelized
turning lanes, where audible tones cannot provide precise enough
information about which crossing is being indicated by the signal.
Vibrotactile information requires physical contact with the signal
hardware. The pedestrian must locate the button and understand the
meaning of the vibrating signal obtained by resting the hand on the
housing of the device. It is essential that vibrotactile signals be
close enough to the curb ramp, near the curb line, so that blind
pedestrians can be aligned and prepared for crossing while still
keeping a hand on the signal.
A figure shows a vertically elongated push button housing. On the top
is a small tactile arrow which can be turned to point across the
street controlled by that push button. On one vertical side of the
housing, going from top to bottom, is a round button, a raised
diagrammatic hand pointing to the button, a silhouette of a person,
and a square array of LEDs. On the other visible vertical side is a
schematic tactile map of the crosswalk. This equipment is manufactured
by Prisma Teknik.
CHARACTERISTICS OF ACCESSIBLE PEDESTRIAN SIGNALS
Information Characteristics
The most important information provided during the WALK interval is:
"When does the crossing interval begin?" The audible or vibrotactile
answer to this question:
o must be readily perceived from where pedestrians begin their
crossings;
o must clearly convey that it is time to walk, and
o must be unambiguous with regard to which street has the WALK
interval.
It should be no louder than necessary.
Volume Control
Most audible pedestrian signals have volume control that is
automatically responsive to ambient (background) sound. A louder tone
will be produced when vehicle and other noise at an intersection is
high, as during rush hour or construction; a quieter sound will be
produced during night-time hours. This is especially helpful in
residential neighborhoods. Some signals can also be pre-set for
varying volume within particular ranges. Most signals with automatic
volume control have a minimum limit placed at about 30 dB and a
maximum limit at about 90 dB.
A signal that is 5 dB above ambient sound as perceived at the
departure curb, is normally considered loud enough to inform
pedestrians who are blind that the WALK interval has begun.
At regularly shaped four-way intersections, the signal does not need
to be heard across the intersection, since the speakers at the
departure and arrival curbs will both operate upon button actuation. A
signal that is unnecessarily loud will not only be perceived as a
neighborhood nuisance, but it may also mask the sounds of turning
vehicles. In Australia, the WALK tone is adjusted to be heard for
about one-third of the width of the crossing.
Localizable Tones
Where intersections are complex, and particularly at crosswalks which
have turns or which are angled relative to the departure sidewalk,
pedestrians who are blind may need information to help them head for
their destination curb. This requires that an audible signal be highly
localizable. The most localizable tones are ones which are
discontinuous and which are of mixed or changing frequencies. Tones
ranging from 500 Hz to 1000 Hz, with higher harmonics, are highly
localizable for most pedestrians, including those having age-related
hearing loss (Hulscher, 1976; San Diego Association of Governments,
1988). Most audible pedestrian signals available in the U.S. are now
pulsed, and most are either mixed frequencies or changing frequencies
such as those resembling birdcalls.
For these signals to be highly localizable, their speakers should be
oriented in line with the relevant crosswalk. If the tone is not
highly localizable and the speaker is not carefully oriented, the
signal may give ambiguous information about which street has the WALK
interval, and ambiguous information for going straight across the
street.
In a typical installation, speakers are actuated simultaneously on
both the corner where the pedestrian is standing and the destination
corner. It is therefore sometimes difficult for blind pedestrians to
determine the direction of the audible pedestrian signal on the
destination corner, even if the tone is highly localizable, because
the tone coming from the destination corner is masked by the sound on
the corner from which the pedestrian is starting the crossing.
Alternating Signal
Research in Montreal (Hall, Rabelle, & Zabihaylo, 1994) has identified
the characteristics of a particularly highly localizable signal.
Orientation and mobility specialists collaborated with an acoustical
engineer to develop a melodic tone which alternated back and forth
across the street.
Blind pedestrians crossed straighter and faster with the alternating
system than with a system in which the tones broadcast in unison from
both ends of the crosswalk. The melody, comprised of highly
localizable frequencies, must be loud enough to be heard across the
intersection. The researchers recommend the use of this signal for
only one crosswalk at an intersection. Pedestrians crossing
perpendicular to the crosswalk having the alternating signal must
interpolate the opposing WALK interval by listening to and analyzing
several signal cycles.
Differentiating Audible Tones
Some audible pedestrian signals utilize two different tones that are
associated with two different crossing directions. The most common
tones are sounds like "cuckoo" and "chirp." The repeating cuckoo sound
is normally used for north/south crosswalks, and the repeating chirp
is normally used for east/west crosswalks. This is the recommended
signal in California and Canada.
Pedestrians report that mockingbirds and catbirds may mimic the
"cuckoo" and "chirp" where the signal is broadcast at every pedestrian
interval. Useful tones must be unique and distinctive and not easily
mistaken for other messages common in the street environment, like the
warning sound of a backing vehicle.
Some APS products have the capability of producing more than two
different tones to accommodate intersections having more than two
intersecting streets. However, it is difficult to interpret the use of
additional tones without specific instruction. Unfamiliar or
non-standard tones will not be useful to pedestrians who are not
familiar with a given intersection.
A figure shows a rectangular box, perforated on one side, with rounded
corners. It has a hinged attachment to the ped-head so the speaker can
be angled variously. This equipment is manufactured by Novax
Industries.
Associating Tones with Direction of Travel
For the two different sounds to be useful, users must remember which
sound goes with which direction, and know their direction of travel.
At intersections that are not aligned according to the primary compass
coordinates, information from paired audible tones may be ambiguous
except to frequent users of those intersections.
In areas where the street system is curvilinear or otherwise
irregular, it may not be apparent to a blind pedestrian that a heading
has changed. In fact, pedestrians may not know the compass orientation
of a route of travel. In research in San Diego (San Diego Association
of Governments, 1988), blind pedestrians were often unable to
associate a given sound with a particular travel direction.
Broadcast Voice Messages
Some systems have the capability of presenting recorded speech
messages telling the name of the street and the status of the signal
cycle (Examples: Campbell/Panich, Novax, Prisma Teknik). In locations
where they have been tried, including Seattle and Philadelphia, there
has been difficulty making the speech information loud enough to be
intelligible over traffic sounds. However, such messages--if
heard--clearly communicate to all pedestrians which street has the
WALK interval.
Research in Clearwater, Florida (Van Houten et al., 1997) with
prototype speech message technology indicates that voice messages can
be used to increase the attention of all pedestrians to turning
vehicles and to decrease pedestrian/motor vehicle conflicts at
signalized intersections.
When the pedestrian push button was pressed, the message was "Please
wait for walk signal."
The message "Look for turning vehicles while crossing [street name]"
began 200 msec before WALK signals were illuminated.
The signal also gave participants who were blind precise information
about the onset of the WALK interval and which street had the WALK
interval.
Audible Push Button Locating Signal
Pedestrians with vision impairments must spend extra time analyzing
traffic patterns in order to identify intersections where actuation is
required. Then they must locate the push button for the crossing they
wish to make. Locating the push button is a major problem for blind
pedestrians (San Diego Association of Governments, 1988).
At pedestrian actuated intersections, it is extremely helpful to have
a quiet tone coming from the vicinity of the push button. This audible
push button locator tone informs pedestrians of the need to use the
push button to actuate the WALK interval and signals the location of
the push button.
Audible push button locating signals typically sound during the DON'T
WALK interval and the clearance interval. They have a slowly repeating
tone or ticking sound which is adjusted to be heard no more than 6 to
12 feet (2 to 4 meters) from the push buttons that serve each end of
the crosswalk.
In available products (Examples: Campbell/Panich, Prisma Teknik, STN
Atlas), the sound has automatic level control. The locator tone
informs pedestrians of the need to push a button, and provides an
audible cue to the destination corner.
A figure shows an oval push button housing, elongated vertically. The
face of this equipment has a large print arrow and a rather small
tactile arrow on the upper half. The arrow can be turned to point to
the street controlled by the push button. On the bottom half is a
large push button. This equipment is available from Campbell/Panich.
Walk Onset Tone
A brief burst of high frequency sound, rapidly decaying to a 500 Hz
WALK tone, is used by one manufacturer (Campbell/Panich) to alert
pedestrians to the exact onset of the WALK interval. This may
encourage faster initiation of crossing, decreasing the likelihood of
conflict between pedestrians and turning vehicles. If crossings are
initiated faster, the intersection is likely to be cleared faster.
Vibrating WALK Signal
In some signals, the push button, a second button on the bottom of the
push button housing, the entire push button housing, or a raised arrow
on the housing vibrates during the WALK interval and, in some cases,
during the clearance and DON'T WALK intervals (Examples:
Campbell/Panich, Georgetown, Polara Engineering, Prisma Teknik). The
vibrating signals may or may not be combined with audible signals. In
signals having both types of information, the vibration is synchronous
with the pulsing of the audible signal (slow during DON'T WALK, and
faster during WALK).
The vibratory information feature lets pedestrians who are deaf-blind
know when the WALK interval is in effect. A vibration-only signal
introduces no noise pollution, but it does not provide information to
other pedestrians, who will not be aware of or use the vibratory
feature. However, vibrotactile signals may be the APS of choice at
medians, slip lanes, and other locations where audible signal messages
might overlap to convey conflicting information.
Location is very important for vibratory-only signals. If the push
button is not located in a good place from which to start the
associated crossing, blind pedestrians must feel the WALK signal and
then find a good starting location and align correctly after its
onset. This may take more than the time allotted in sequencing
programs to initiate a crossing. At a crowded corner, it may be
difficult for pedestrians who are blind to make their way up to the
button.
A figure shows a rectangular sign retrofitted onto a round push button
housing. The sign extends upward from the push button. At the top of
the rectangle is a walking man symbol. Below this is a large tactile
arrow with a raised street name (Dale) in all caps, and the raised
numeral 4 at the tip of the arrow. The arrow points toward the street
to be crossed, and the 4 indicates that there are 4 lanes to be
crossed. The large arrow vibrates on WALK. Below the large arrow is a
high contrast print arrow.
Actuation Indicator
Either a light, a tone, or both may indicate to pedestrians that their
actuation request has been received (Examples: Campbell/Panich, Prisma
Teknik). The indicator assures pedestrians that the device is working,
thereby encouraging pedestrians to wait until the onset of the WALK
interval. A light is helpful to persons with low vision, but persons
who are blind require a tone.
Tactile Information
A raised arrow on the push button housing helps users know which
street is controlled by a push button. It is of minimal assistance in
aligning for a crossing, however. The arrows that work best for
persons who are blind are ones that have a relatively long shaft and
are oriented so that they can be read with the hand held in a
horizontal position. Arrows should have good visual contrast with
their background so that all users, including those having low vision,
will see them readily.
One signal (manufactured by Polara Engineering) provides the name of
the associated street in braille and raised type on a large,
vibrating, tactile arrow placed above the push button. A Scandinavian
push button-integrated signal (manufactured by Prisma Teknik) can
incorporate a raised schematic map showing what will be encountered as
the pedestrian negotiates the crosswalk controlled by that push
button. Map information includes:
o the number of lanes to be crossed;
o whether these are vehicular or bicycle lanes or trolley tracks;
o which direction traffic will be coming from in each lane, and
o whether there is a median.
A California manufacturer (Polara Engineering) is working on a system
of tactile symbols which will provide information such as the shape of
the intersection, and whether turning traffic is permitted during the
WALK interval.
A figure shows an example of a tactile map which is an optional
feature on the Prisma Teknik push button. An arrow at the bottom
points upward. It indicates where the pedestrian is starting and the
direction of travel. A horizontal bar above the arrow indicates the
down curb. A vertical line extending upwards from the curb line
indicates the crosswalk itself. Along this line, reading from bottom
to top, are two small rectangles to the left of the crosswalk line
indicating two vehicular lanes with traffic coming from the left, then
an oval interrupting the crosswalk line indicating an island or median
across the crosswalk, and then two small rectangles to the right of
the crosswalk line indicating two vehicular lanes with traffic coming
from the right. At the upper end of the crosswalk line is a horizontal
line indicating the up curb. It can be seen that each symbol is a
separate piece, so the maps can be assembled to correctly show the
crosswalk at each push button.
Separate Actuation of the Audible Signal
Several jurisdictions report the use of special actuating buttons or
systems for accessible signals that are subsidiary to the standard
pedestrian button. Devices may actuate an audible or vibrotactile
signal only in response to a specific call.
Two devices (Georgetown and Novax) can be optionally equipped such
that a pedestrian must push and hold the button for an additional
period of time in order to actuate the audible feature. Other systems
rely on a separate actuating button, which may have a braille label.
Blind pedestrians who don't wish to add noise to the environment or to
call attention to themselves can actuate the WALK interval without
actuating the accessible signal. Pedestrians who are not aware of
local practice may not be able to call the accessible signal.
DETERMINING WHEN TO INSTALL APS
Introduction
In some countries APS are required wherever new pedestrian signals are
installed. In the U.S., however, APS have been viewed as an individual
accommodation, installed upon request along a specific route of
travel.
It is likely that the recent passage of the Transportation Equity Act
for the 21st Century (TEA-21), the successor to ISTEA, will stimulate
increased attention to APS as a standard pedestrian safety feature.
The Department of Transportation will develop guidance on a wide range
of pedestrian and bicycle issues, including APS. Transportation
standards, documents, manuals, and good practice recommendations will
be updated over the next few years to reflect this broader view. The
Institute of Transportation Engineers has established a committee on
accessible intersections charged to develop a toolbox of resources
that traffic engineers can use to make information at intersections
available to pedestrians with vision impairments.
Since pedestrians who are blind have sufficient acoustic information
for crossing many streets safely, how are engineers to decide which
signalized intersections shall have APS?
A number of U.S. jurisdictions have well-articulated systems for
determining whether an APS is warranted. Each involves participation
of one or more representatives of at least three groups of experts:
traffic engineers, orientation and mobility specialists, and
pedestrians who are blind. Additional information may be obtained from
transportation agencies listed under "Sources of Information" later in
this document.
San Diego and Los Angeles have highly structured rating scales and
require a minimum number of points to warrant installation of APS. The
process used in Portland, Oregon is less structured.
APS Need Evaluation Factors
Factors that these and other jurisdictions consider in evaluating
signalized intersections to determine whether APS are warranted
include:
o proximity to a facility for persons who are blind;
o proximity to alternate crossings, proximity to transit stops, and
proximity to key facilities used by all pedestrians;
o intersection configuration and width of street;
o vehicle speed;
o traffic volume (both heavy and light);
o pedestrian accident records;
o demonstrated need or user request;
o presence of pedestrian push buttons;
o surrounding land use and neighborhood acceptance; and
o existence of a signal which is susceptible to retrofitting.
Cost of Evaluation Versus Standard Implementation
At least one small city has determined that the expense of evaluating
intersections for APS installation is likely to be higher than simply
integrating APS in the pedestrian signal, where one is provided.
Corvallis, Oregon has provided APS at all signalized intersections.
They have found that audible prompts get pedestrians moving faster and
are particularly useful in advising persons with cognitive
disabilities when to cross the street. If APS are to be installed at
all signalized intersections, it is important that signals from one
intersection cannot be heard at other intersections.
Summary
While point ratings based upon factors outlined above may be useful in
evaluating priorities for the installation of APS at specific
locations, it should be kept in mind that state and local governments
may be held legally liable if a person who is blind or visually
impaired is injured as a result of the absence of APS, particularly if
there has been a request for APS at the relevant intersection.
Furthermore, the information provided by APS may be necessary at any
time, along any route, to residents, occasional travelers, and
visitors. Thus, warranting schemes should place only limited emphasis
on factors related to frequency or likelihood of use. Of greater
importance are factors related to determining whether sufficient
acoustic information exists--at all times--to permit safe crossing at
a particular intersection.
Too little traffic is as great a problem for pedestrians who are blind
as is too much traffic. Blind pedestrians must be able to hear a surge
of traffic parallel to their direction of travel in order to know when
the WALK interval begins.
Intersections that may require evaluation for APS installation include
those with:
o very wide crossings;
o secondary streets having little traffic;
o non-orthogonal or skewed crossings;
o T-shaped intersections;
o high volumes of turning vehicles;
o split-phase signal timing; and
o noisy locations.
Where these conditions occur, it may be impossible for a pedestrian
who is blind to determine the onset of the WALK interval by listening
for the onset of parallel traffic or to obtain usable orientation and
directional information about the crossing from the cues that are
available.
SPECIFYING ACCESSIBLE PEDESTRIAN SIGNALS
Standards and Technical Provisions
In many countries, APS technology is specified in regulations. The
most prescriptive standard seems to be that of Australia, which is met
by the Audio Tactile Push Button with a locator tone manufactured by
Bob Panich Consultancy. Canada's standard is much less prescriptive,
and is similar to that of the state of California. Signals
manufactured by Intersection Development Corp., Mallory, Novax
Industries, and Wilcox Sales meet these specifications.
The International Standards Organization (ISO) has recently developed
a draft standard "Technical aids for vision and vision and hearing
impaired persons, Acoustic and tactile signals for traffic lights";
signals manufactured by Bob Panich Consultancy, Prisma Teknik and STN
Atlas meet the criteria of the current draft. See "Sources of
Information" later in this document to obtain standards.
Push Button Criteria
Pedestrians who have vision impairments need to know if an
intersection is designed to require pedestrian actuation of the WALK
cycle. This information can be provided by an accessible push button.
The most important characteristics of accessible push buttons are:
o a locating tone if actuation requires use of a push button;
o a faster, repeating tone during WALK; and
o a tactile arrow to indicate which crosswalk is governed by the push
button.
Desirable optional characteristics include:
o a change tone at the onset of WALK;
o a vibration on WALK;
o audible and visible actuation indicators; and
o a tactile map, symbols, or text providing intersection information.
Broadcast Audible Signal Criteria
The most important functional characteristics of APS which broadcast
audible information on the status of the signal cycle from the
ped-head are:
o a highly localizable sound;
o an unambiguous indication of which street has the WALK interval; and
o a sound volume responsive to ambient sound.
Desirable optional characteristics include:
o alternating tones; and
o a different tone for opposing crossings.
Transmitted Audible Signal Criteria
The most important considerations for APS which transmit personal
messages are:
o an unambiguous message set;
o signal status messages which can be heard only within the crosswalk;
and
o a proactive system for distributing receivers to residents and
visitors.
Desirable optional characteristics include:
o naming the intersecting street in the signal messages; and
o providing additional location information that can be picked up as
the traveler approaches the intersection.
Vibrotactile Signal Criteria
Vibrotactile signals must be installed within the width of the
crosswalk near the curb line of the sidewalk so that users can rest a
hand on the signal while simultaneously being aligned and prepared to
cross.
INSTALLING ACCESSIBLE PEDESTRIAN SIGNALS
Precise Orientation of Speakers and Transmitters
Precise orientation is critical. If a speaker or transmitter is
oriented even a few degrees out of alignment with the associated
crosswalk, pedestrians may inadvertently travel out of the crosswalk.
Audible signals should be mounted within the crosswalk; where two
speakers are used on the same corner, they should be horizontally
separated by at least 10 feet (3 meters).
Sound Level
The sound level of the speakers should be carefully set. Sound should
be between 30 dB minimum and 90 dB maximum. At no time should sound be
more than 5 dB above ambient sound. At crosswalks where pedestrians
who are blind need to know only the onset of WALK, sound pressure
levels should be measured from the corner. At crosswalks where
directional guidance is needed, such as at very wide streets, or at
irregular or complex intersections, sound pressure level (dB) should
be measured from the middle of the street.
Location of Push Buttons
Push buttons must be installed as near the crosswalk as possible,
preferably on the sidewalk within the width of the crosswalk
connection. Vibration-only devices should be installed within the
width of the crosswalk near the curb line of the sidewalk. Where push
buttons emit tones, paired devices signaling perpendicular crossings
should be separated as much as crosswalk location permits. Tactile
signage can be used to identify which crossing is controlled. Because
all pedestrians will use the push button at an actuated crossing, the
device should be located in close proximity to the top landing of the
curb ramp serving that crossing and within accessible reach range for
use from a wheelchair.
PEDESTRIAN DETECTION TECHNOLOGY
Introduction
Pedestrian detection technology can be of particular benefit to
persons who are blind if the system incorporates audible and/or
tactile crossing information. Systems that replace pedestrian
actuation with automatic sensing to trigger a WALK cycle should
provide APS to signal the crossing interval, since the cycle will not
otherwise provide sufficient cues for analysis by a blind user.
PUFFIN Crossing
An excellent example of the use of detection technology is the
"Pedestrian User-Friendly INtelligent (PUFFIN) crossing in use in
England since 1993 (Department of Transport, 1993). PUFFIN crossings,
with equipment manufactured by Microsense Systems, Ltd., employ
pedestrian detectors for both the pedestrian waiting area and the
crosswalk.
In PUFFIN crossings, visual WALK/DON'T WALK indicators are located on
the same end of the crosswalk as the waiting pedestrian. They are
oriented perpendicular to the street at the right edge of the
crosswalk so that the pedestrian can simultaneously watch the ped-head
and the approaching traffic in the nearest lane. Because the ped-heads
can be viewed close up, pedestrians who have low vision are often able
to see the visual signals. The visual pedestrian signals show either a
green man indicating that the pedestrian may start crossing, or a red
man indicating that the pedestrian should not start crossing. There is
no intermediate or ambiguous flashing symbol.
Waiting Area Detectors
Waiting area detectors may be either pressure mats with piezo-electric
sensors, infrared or microwave detectors mounted on the signal pole,
or video cameras serving remote sensor software. After a pedestrian
has pressed a push button to actuate the WALK interval, detectors
confirm the presence of pedestrians standing near the crossing. If the
pedestrian disappears before the onset of the walk interval, the call
for the pedestrian phase is canceled. Pedestrians who are
vision-impaired must be able to locate the push-button, the waiting
area, and the crosswalk if such detectors are to be effective. In
these and in similar systems that rely wholly on sensors to actuate
the pedestrian phase, APS will be necessary to signal the onset of the
WALK interval.
Crosswalk Detectors
Crosswalk detectors are infrared sensors that respond to pedestrians
moving in the crosswalk. As long as a pedestrian is detected in the
crosswalk, a preset extension is added to the pedestrian clearance
interval, enabling later-starting or slower moving pedestrians to
clear the intersection before vehicular traffic resumes.
Similar pedestrian detection technologies are in use in the
Netherlands, Australia and New Zealand, where they also improve safety
and efficiency of street crossings for pedestrians who have vision
impairments.
ACCESSIBLE PEDESTRIAN SIGNALS:
PRODUCT FUNCTIONAL CHARACTERISTICS
[Characteristics of eleven products are described in a matrix format,
giving the following information for each product.]
1. Type of product: Speaker mounted in the ped-head (visual pedestrian
signal); transmitter mounted in the ped-head; or push-button
integrated.
2. Audible walk signal characteristics: voice; bell; buzzer;
birdcalls; ticker; or tones.
3. Sound volume: fixed; variable by the installer; automatically
varying in relation to ambient sound level; variable by the user; or
audible only at user request.
4. Presence of an audible locating tone for a pedestrian push button.
5. Presence of a special walk onset tone at the beginning of the walk
interval.
6. Presence of a vibrating walk signal.
7. Actuation indication: either a light or a tone to indicate that a
pedestrian has pushed the button to request a walk interval.
8. Tactile information: either an arrow to indicate which street a
push button controls, or additional tactile information about street
geometry.
9. Street name.
For each product below, this text version will state whether the
characteristic is a standard feature or is optional. Information on
product sources follows this text.
Campbell/Panich. Push button integrated - standard; tones - standard;
voice or birdcalls - optional, automatically variable volume -
standard; actuation indication (light) - optional; tactile arrow -
standard.
Georgetown. Push button integrated - standard; buzzer - optional,
actuated only when button is depressed for at least three seconds -
optional; audible locating signal - optional; vibrating walk signal -
standard; tactile arrow - standard.
Intersection Development Corporation. Speaker mounted on or in the
ped-head - standard; birdcalls (cuckoo and chirp to indicate which
crosswalk has the walk interval) - standard; automatically variable
volume - standard.
Mallory. Speaker mounted on or in the ped-head, providing either
birdcalls or tones - standard; fixed sound volume - standard. This
product is a component for a ped-head.
Novax Industries. Speaker mounted on or in the ped-head - standard;
birdcalls - standard; optional sounds include voice, bell, buzzer,
ticker, and tones; sound volume can be set by installer within maximum
and minimum limits, and then automatically variable volume - standard.
A separate push button product actuates an audible signal only when
the button is depressed for at least three seconds.
Polara Engineering. Push button integrated - standard; tones -
optional; vibrating walk signal - standard; audible locating signal -
optional; tactile arrow - standard; street name in braille and raised
print - standard; street geometry information - optional. This product
retrofits an existing push button.
Prisma Teknik. Push button integrated - standard; tone - standard;
voice - optional; sound volume set by installer within maximum and
minimum limits, and then automatically variable volume - standard;
audible locating signal - standard; vibrating walk signal - optional;
actuation indicator (light and tone) - standard; tactile arrow -
standard; tactile crosswalk map - optional.
Relume. Ped-head mounted transmitter - standard. Speech message says
"Proceed with caution" during walk interval, and "Don't walk" during
clearance and don't walk intervals. Requires hand-held receiver.
STN Atlas. Speaker mounted near ped-head - standard; WALK tones -
standard; automatically variable volume - standard; audible locating
signal (ticker) - standard.
Talking Signs. Ped-head mounted transmitter - standard. Repeating
speech message says "Walk sign" and street name during walk interval,
and "Wait" and street name during clearance and don't walk intervals.
Volume variable by user. Requires hand-held receiver.
Wilcox Sales. Speaker mounted on ped-head - standard; birdcalls -
standard; sound volume variable by installer - standard; automatically
variable volume - optional.
APS PRODUCT SOURCES
Bob Panich Consultancy Pty. Ltd.
48 Church Street, P.O. Box 360
Ryde NSW 2112, Australia
Voice: 61 2 9809 6499
Fax: 61 2 9809 6962
E-mail: [log in to unmask]
Website: people.enternet.com.au/~panich
Product: Audio Tactile PB
Dick Campbell Company
1486 Northwest 70th Street
Seattle, Washington 98117
Voice: (206) 782-1991
Fax: (206) 782-2092
Email: [log in to unmask]
Product: Audio Tactile PB
Georgetown Electric, Ltd.
2507 West Second Street
Wilmington, Delaware 19805
Voice: (302) 652-4835
Fax: (302) 652-6447
Product: VIPB
Intersection Development Corporation
9300 East Hall Road,
Downey, California 90241
Voice: (800) 733-7872 or (562) 923-9600
Fax: (562) 923-7555
Website: www.idc-traffic.com
Product: APS-10
Mallory/North American Capacitor Co.
P.O. Box 1284
Indianapolis, Indiana 46206-1284
Voice: (317) 273-0090
Fax: (317) 273-2400
Product: VSB 110
NOVAX Industries Corporation
658 Derwent Way
New Westminster BC V3M5P8 Canada
Voice: (604) 525-5644
Fax: (604) 525-2739
Website: www.novax.com
Product: DS-100
Polara Engineering, Inc.
4115 Artesia Avenue
Fullerton, California 92833-2520
Voice: (714) 521-0900
Fax: (714) 522-8001
Email: [log in to unmask]
Product: TPA
Prisma Teknik AB
P.O. Box 5, S-543 21
Tibro, Sweden
Voice: (46) 504 150 40
Fax: (46) 504 141 41
Email: [log in to unmask]
Website: www.prismateknik.com
Product: Prisma TS
Relume Corporation
64 Park Street
Troy, Michigan 48083
Voice: (248) 585-2640 or (888) 7RELUME
Fax: (248) 585-1909
STN Atlas Elektronik GmbH
Behringstrasse 120
D 22763 Hamburg, Germany
Voice: (49) 40 88 25 2155
Fax: (49) 40 88 25 4111
Product: AUDIAM
Talking Signs, Inc.
812 North Boulevard
Baton Rouge, Louisiana 70802
Voice: (888) 825-5746 or (504) 344-2812
Fax: (504) 344-2811
Email: [log in to unmask]
Wilcox Sales Company
1738 Finecroft Drive
Claremont, California 91711-2411
Voice: (909) 624-6674
Fax: (909) 624-8207
Product: PS/A 10
SOURCES OF INFORMATION
California Department of Transportation
Traffic Manual Metrics, Rev. 1996
1120 North Street
Sacramento, California 95814
Voice: (916) 654-5267 or (916) 654-2852
City of Los Angeles, California
Adaptive Device Study Worksheet
Brian Gallagher, PE
Department of Transportation
City of Los Angeles
221 Figueroa Street, Suite 300
Los Angeles, California 90012
Voice: (213) 580-5398
City of Portland, Oregon
Guidelines for Installing Audible Pedestrian Traffic Signals
Linda Ginenthal, Community Traffic Safety Program
City of Portland
Office of Transportation
1120 SW Fifth Avenue, Room 730
Portland, Oregon 97204
Voice: (503) 823-5266
E-mail: [log in to unmask]
City of San Diego, California
Audible Pedestrian Traffic Signals for the Blind
Intersection Evaluation Procedure
Patricia Sieglen, Disability Services Coordinator
City of San Diego
1200 Third Avenue, Suite 924
San Diego, California 92101
Voice: (619) 236-5979
Fax: (619) 236-5596
Department of Transport
Network Management and
Driver Information Division
St. Christopher House
Southwark, London
England SE1 0TE
International Standards Organization
Secretariat of ISO/TC 173/WG6
Mr. Gerald Kuso
Osterreichisches Normungsinstitut
Heinistrasse 38
A-1020 Wien, Austria
Voice: (43) 1 213 00 714
Fax: (43) 1 213 00 722
Microsense Systems, Ltd.
Meon House, 10 Barnes Wallis Road
Segensworth, Fareham, Hampshire
England, PO15 5TT
Voice: (44) 1489 571979
Fax: (44) 1489 575616
Standards Australia
Pedestrian Push-button Assemblies
1 The Crescent, Homebush 2140
(PO Box 1055, Strathfield 2135)
Australia
Voice: (61) 2 9746 4600
Fax: (61) 2 9746 3333
Transportation Association of Canada
TAC Manual of Uniform Traffic Control Devices, 1994
2323 St. Laureat Boulevard
Ottawa, Ontario K1G 4J8 Canada
Voice: (613) 736-1350
Fax: (613) 736-1395
E-mail: [log in to unmask]
Website: www.tac-atc.ca/
U.S. Architectural and Transportation Barriers Compliance Board
(the Access Board)
1331 F Street NW, #1000
Washington, DC 20004-1111
Voice: (202) 272-5434; Technical Assistance Line: (800) 872-2253
TTY: (202) 272-5449; Technical Assistance Line: (800) 993-2822
Fax: (202) 272-5447
E-mail: [log in to unmask]
Website: www.access-board.gov
REFERENCES
Bentzen, B.L. & Barlow, J.B. (1995). Impact of curb ramps on safety of
persons who are blind. Journal of Visual Impairment and Blindness. 89,
319-328.
Crandall, W., Bentzen, B., & Myers, L. (1998). Smith-Kettlewell
Research on the use of Talking Signs (reg. tm) at light controlled
street crossings. Smith-Kettlewell Rehabilitation Engineering Research
Center, San Francisco. Report to National Institute on Disability and
Rehabilitation Research.
Department of Transport (1993). The use of PUFFIN pedestrian
crossings. London: Department of Transport, Network Management and
Driver Information Division.
Hall, G., Rabelle, A. & Zabihaylo, C. (1994). Audible traffic signals:
A new definition. Montreal: Montreal Association for the Blind.
Hauger, S., Rigby, J., Safewright, M & McAuley, W. (1996). Detectable
warning surfaces at curb ramps. Journal of Visual Impairment and
Blindness. 90, 512-525.
Hulscher, F. (1976). Traffic signal facilities for blind pedestrians.
Australian Road Research Board Proceedings 8, 13-26.
San Diego Association of Governments (1988). Evaluation of audible
pedestrian traffic signals.
Van Houten, R., Malenfant, J., Van Houten, J. & Retting, R. (1997).
Using auditory pedestrian signals to reduce pedestrian and vehicle
conflicts. Transportation Research Record No. 1578. Washington, DC:
National Academy Press.
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