20-06-2014, 02:31 PM
Using a Smartphone App to Assist the Visually Impaired at Signalized Intersections
Using a Smartphone App to Assist the.pdf (Size: 1.29 MB / Downloads: 20)
INTRODUCTION
Individuals who are blind or visually impaired use the auditory and limited visual information
that they can gather to make safe crossing decisions often report being dissatisfied with a general
lack of information while crossing intersections, as found by Ponchillia, Rak, Freeland, and
LaGrow (2007). This may explain why a study of blind pedestrian behavior in three cities found
that only 49% of the crossings started during the walk interval (Barlow, Bentzen, & Bond, 2005).
They also found that 27% of all crossings (that did not involve outside assistance) ended after the
onset of the perpendicular traffic stream.
At crossings where using a pushbutton was required, Barlow, et al. (2005) found that few (0% -
16% depending on the city sampled) looked for and found the button; they also began walking
only 20% of the time during the walk signal compared to 72% of the time when the pedestrian
phase was on recall (i.e., included in every cycle). This may be because searching for the button
often requires the pedestrian to move from their path of travel, which is often used as an
alignment cue to make sure they are crossing straight. This suggests that there is room for
improvement in terms of the design and accessibility of both accessible pedestrian signals (APS)
and non-APS crosswalk signals for blind and low-vision pedestrians.
In addition, Barlow et al. (2005) found that although 72% started with appropriate alignment,
location, or both, 42% ended their crossing maneuver outside the crosswalk. To this end, Guth,
Ashmead, Long, and Wall (2005) found that site-specific characteristics (e.g., treatments such as
rumble strips or speed countermeasures) appeared to have a greater impact on reducing the
number of conflicts between pedestrians and vehicles than did a mobility device (e.g., cane or
seeing-eye dog). Therefore, enhancing pedestrians’ ability to perceive useful cues at an
intersection may be an effective method of reducing crash events.
Navigation and Wayfinding for the Blind
may be arguable that providing wayfinding technology for the blind and visually impaired may
undermine the maintenance of their learned techniques. However, the application to improve
safety and increase capability for the visually impaired is more likely to outweigh the overall
cost (Loomis et al., 2007). Navigation and wayfinding involve with dynamically monitoring a
person’s position and orientation with respect to the immediate environment and destination
(Klatzky et al., 1998, 1999; Aslan and Krüger, 2004; Rieser, 2007). Navigation usually implies
that a user will follow a predetermined route or path between a specific origin and destination.
Navigation is often referred to as an optimal path based on a specific goal, such as shortest time,
distance, minimum cost, etc. However, wayfinding refers to the process of finding a path, not
necessary traveled previously, between a pair of origin and destination. The wayfinding process
is more adventurous and exploratory.
Blind Pedestrian at Intersection Crossing
People with vision impairment use auditory and limited visual information that they can gather to
make safe crossing decision at signal intersection. They generally have difficulty crossing
intersections due to the lack of information available to them about the traffic and geometry at
intersections (Ponchillia et al., 2007). A study of blind pedestrian's behavior in three cities found
that only 49% of the crossings started during the walk interval (Barlow et al., 2005). The study
also found that 27% of all crossings (that did not involve outside assistance) ended after the onset
of the perpendicular traffic stream.
At crossings where using a pushbutton is required, Barlow, et al. (2005) found that few (0% -
16%) looked for and found the button; they also began walking only 20% of the time during the
walk signal as compared to 72% of the time when the pedestrian phase was on recall. The reason
may be because searching for the button often requires the pedestrian to move away from their
path of travel, which is often used as an alignment cue for crossing. In addition, Barlow et al.
(2005) found that although 72% of blind participants started with appropriate alignment,
location, or both, 42% ended their crossing maneuver outside the crosswalk. Guth et al. (2007)
found that site-specific characteristics (for example, treatments such as rumble strips or speed
countermeasures) appeared to have a greater impact on reducing the number of conflicts between
pedestrians and vehicles than did a mobility device (e.g., cane or guide dog). Therefore,
enhancing pedestrians’ ability to perceive useful cues at an intersection may be an effective
method of reducing crash events. There is room for improvement in terms of the design and
accessibility of both accessible pedestrian signals (APS) and non-APS crosswalk signals for
blind and low-vision pedestrians.
Navigation Technology and Location Based Services (LBS) for the Blind
Development of travelling aids based on global positioning has a long history. The first satellite
navigation system, used by US Navy, was first tested in 1960. The use of GPS to guide blind,
visual impaired or elderly people has been researched extensively (Garaj, 2001; Gill, 1997; Helal
et al., 2001). Tjan et al. (2005) designed and implemented a Digital Sign System (DSS) based on
low-cost passive retro-reflective tags printed with specially designed patterns. Blind or visually
impaired pedestrians can use a handheld camera and machine-vision system to identify and
navigate through unfamiliar indoor environment. Bae et al. (2009) evaluated a location tracking
system using IEEE 802.11b Wi-Fi system to analyze the requirements of location based services
in an indoor environment.
MOBILE ACCESSIBLE PEDESTRIAN SIGNAL (MAPS)
After receiving orientation and mobility (O&M) training from O&M specialists, people with
vision impairment usually can travel independently to known places along familiar routes by
relying on a white cane or guide dog. However, neither the white cane nor the guide dog
provides spatial awareness along a path or traffic signal information at an intersection. Travelers
with vision impairment may have difficulty planning or feel anxious about unfamiliar routes,
often obtaining and closely following detailed turn-by-turn instructions to reach new
destinations.
In addition to a cane and guide dog, many aids based on various types of technologies have been
developed in the past. Several of these are commercially available to support both indoor and
outdoor wayfinding and navigation for people who are blind. Several of these technologies aim
to address the indoor and outdoor wayfinding problem separately. These solutions generally do
not provide intersection geometry and traffic signal information for pedestrians who are blind or
visually impaired.
The newer generation of Accessible Pedestrian Signal (APS) system incorporates many of the
shortcomings from the earlier system. It provides audible and vibrotactile indication of the
‘Walk’ signal. A pushbutton locator tone that repeats constantly at 1Hz is added to provide
information about the presence and location of a pushbutton. Currently, each APS system costs
over $6,000 per intersection plus labor. There is limited number of intersections equipped with
the APS system due to limited amount of resources available to the public agency. In US, there is
no standard pushbutton location and it often requires additional stub for installing pushbutton
System Objectives
The first objective is to provide intersection geometry, traffic signal information and automatic
pedestrian phase request through a smartphone device. A smartphone application prototype will
integrate available sensors on the phone to determine a user location and orientation with respect
to an intersection. The smartphone app then wirelessly communicates with a traffic controller
and receives near real-time signal timing and phasing updates. Corresponding signal phasing
information is sent to smartphone according to the desired direction of crossing as confirmed by
the user. After receiving confirmation from users, the system will then provide timing
information of corresponding pedestrian phase to users. Warning signals such as ‘Do not walk’
or ‘Walk phase is on, # sec left’ will be broadcasted through Text-to-Speech (TTS) interface to
support decision making at crossing. Automatic pedestrian pushbutton request can also be sent to
signal controller for registered blind, visually impaired, elderly or disabled pedestrians when they
confirm the desired direction of crossing.
EXPERIMENT DESIGN
Minnesota Institutional Review Board (IRB Code # 1112S07962).
3.1 Locations
Two intersections in Golden Valley west of City of Minneapolis were identified and
recommended by Orientation and Mobility (O&M) specialist for field experiment. Intersection
#1 is located at Winnetka Avenue and Golden Valley Road. The Winnetka Avenue, five lanes,
goes in north-south direction and the Golden Valley Road, four lanes, is in the east-west
direction. This intersection is installed with APS system manufactured by Polara Engineering,
Inc. (http://www.polara). Intersection #2, couple blocks away from the first intersection is
located at Rhode Island Avenue and Highway 55 (Olson Memorial Highway). The Rhode Island
Avenue, four lanes, goes in north-south direction and Highway 55, seven lanes, is in the eastwest
direction. This intersection does not have APS system installed. Pedestrians are required to
use existing pushbutton to cross the intersection. Crossing experiments at intersection #1 and #2
were conducted on separate Friday on April 13 & 20, 2012, respectively.
Materials
The experiment at intersection #1 took place nearby a commercial area on a light raining day
from 7:40 AM to 5:30PM. The experiment at intersection #2, two blocks away from the first
intersection, took place on a bright sunny day from 7:40 AM to 5:30PM. Sidewalk areas were
clear with no obstacles at both locations. However, the sidewalk surface, at couple spots, was a
bit uneven at intersection #2. A traffic data collection unit (DCU) and a relay IO module were
installed in the controller cabinet at intersection #2 to provide signal information to smartphone
users. Survey questionnaire regarding usability, acceptance, and trust of the smartphone-based
traffic signal system was read to each individual and their responses were recorded on the
questionnaire. See Appendix B for questionnaire details
Procedures
research team member before and after each crossing task. The crossing tasks and interviews
focus on participants’ experiences while crossing signalized intersections, using audible
pedestrian signals, or a smartphone-based accessible pedestrian signal device provided by the
research team.
For each crossing task, a certified O&M specialist brought each participant to a starting point
which was located about 100 to 200 feet (north) away from the north-east corner of the
intersection, as illustrated in Figure 3-1. Visually impaired participants were asked to travel
along the sidewalk using their own navigational skills to reach the corner of the intersection.
While at the intersection, the visually impaired participants need to find and use the pushbutton
to request a pedestrian walk signal or use the smartphone-based pedestrian signal device to
determine when it is possible to cross. Participants then cross the street that is perpendicular to
the sidewalk they just travelled and arrive at the other side of street.
SUMMARY AND CONCLUSION
People with vision impairment generally have difficulty crossing intersections due to lack of
information available to them about the traffic, signal and intersection geometry. Among the
intersection crossing sub-tasks, locating the crosswalk, determining when to cross and
maintaining alignment with the crosswalk while crossing are the most difficult tasks for the blind
or visually impaired to execute. The current Accessible Pedestrian Signal (APS) system requires
the blind to search for a pushbutton if one even exists. It often requires the pedestrian to move
away from their path of travel, which is often used as an alignment cue for crossing. Due to the
high cost of the APS installation, most agencies do not deploy them at all signalized
intersections. In addition to the installation and maintenance costs that accrue to the local traffic
agency, current APS systems contribute significant “noise” to the local neighborhood.
Furthermore, the auditory guiding cues provided by the APS are often inaudible because of the
ambient traffic noise associated with rush hour. There is room for improvement in terms of the
design and accessibility of both APS and non-APS crosswalk signals for blind and low-vision
pedestrians.
Among the intersection crossing sub-tasks, locating crosswalk, determining when to cross and
maintaining alignment to crosswalk while crossing are the most difficult tasks for the blind and
visually impaired. We have interviewed ten blind and low-vision people to understand what
types of information they use at intersection crossings and identified information types that could
assist them. Six high-level recommendations emerged for the design of MAPS: