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SUMMARY
Crossing Solutions at Roundabouts
and Channelized Turn Lanes for Pedestrians
with Vision Disabilities
This report explores concerns over the accessibility of two complex intersection forms for
pedestrians who are blind: intersections with channelized right turn lanes and modern
roundabouts with one-lane and two-lane approaches. Based on the findings of this research
project, significant impediments to the accessibility of these sites exist for pedestrians who
are blind, but some crossing solutions can increase the accessibility in terms of improving
safety and reducing delay. The following sections summarize the research approach and
major conclusions of this study.
Project Overview
Objectives
The guidance in this report is intended to provide practitioners with useful information
related to establishing safe crossings at roundabouts and channelized turn lanes (CTLs) for
pedestrians who are blind. The specific objectives of this project were to:
· Identify and field test crossing treatments with the potential to enhance accessibility for
pedestrians who are blind,
· Formulate and apply an evaluation framework and associated performance measures that
can quantify accessibility,
· Develop approaches to extend the findings to other sites through statistical modeling and
microsimulation, and
· Discuss implications of the results for engineering practice and the ongoing accessibility
debate.
This report is not intended to provide practitioners with rigid requirements of when to
install specific treatments. To do so would involve policy decisions that are beyond the scope
of this effort. Instead, the report provides pertinent information on the concept of accessi-
bility and how to provide improved crossing environments based on the crossing task for a
visually impaired pedestrian.
Problem Definition
The crossing task for blind pedestrians consists of four principal tasks that need to be mas-
tered to successfully cross the street:
1. Finding the crosswalk and identifying the intended crossing location at an unknown
intersection,
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2. Aligning to cross to establish a correct initial heading at a crosswalk that may or may not
be aligned perpendicular with the sidewalk,
3. Deciding when to cross in an environment of largely uninterrupted traffic flow requiring
the identification of appropriate gaps in traffic or crossing opportunities in front of yield-
ing vehicles, and
4. Maintaining alignment while crossing multiple lanes over the length of the entire cross-
walk until the far side of the roadway is reached.
The crossing task at channelized right turn lanes and modern roundabouts is challeng-
ing due to the prevailing curved vehicle trajectories and complicated by the absence of a
pedestrian signal at most crossings. While many pedestrian crossings are unsignalized,
traffic patterns at a conventional orthogonal intersection are more readily interpreted by
a blind traveler. At pedestrian crossings with signals, the presence of an accessible pedes-
trian signal (APS) can provide further information to a blind traveler about the present
signal phase and the anticipated traffic patterns. At the crosswalks studied in this research,
no signals were present (in the base condition), which resulted in a largely uninterrupted flow
of traffic. The geometric configuration of the intersection can further result in elevated speeds
at the crosswalk, and busy traffic volumes can contribute to high ambient noise levels, fur-
ther complicating the task of correctly identifying vehicle trajectories based on auditory infor-
mation alone. Various prior research efforts have documented the crossing challenges for
pedestrians who are blind at roundabouts and intersections with channelized turn lanes, and
these findings have been confirmed in this project.
Research Approach
Site and Treatment Selection
The NCHRP Project 3-78A research effort was focused on the evaluation of infrastructure-
based treatments that are within the jurisdiction of a public agency. Other agent-based treat-
ments that may be carried out by the pedestrian were considered to be outside the scope of
this effort. The project began with an extensive list of infrastructure-based treatments that
was narrowed down through an internal team survey process to a small subset of treatments,
that were deemed to have the greatest chance for success and that had not previously been
evaluated through research. The list of treatments conceptually falls along a two-dimensional
performance assessment matrix:
1. The degree of control over critical pedestrian and driver behaviors, and
2. The costs for acquisition, installation, and maintenance by an agency.
The research team carefully matched the degree of control to the expected crossing chal-
lenges at a test location, while striving to minimize agency cost. As a result, a two-lane round-
about crossing was outfitted with a signalization device and speed-reducing traffic calming
features while a single-lane channelized turn lane was outfitted with flashing beacons and
sound-amplifying pavement treatments. The number of treatment field installations was con-
strained by the team's ability to identify agencies willing to install and incur the treatment
costs. Additional treatments that were not formally installed and evaluated are discussed
throughout the report and appendices. (Appendix B through Appendix N are contained in
NCHRP Web-Only Document 160, available on the TRB website.)
Test sites were selected on the basis of representative geometry of roundabout and chan-
nelized turn lane designs, the provision of pedestrian facilities, the existence of a sufficiently
large pool of blind study participants, and ultimately the willingness of the local road agency
to support the research team in treatment installation and evaluation.
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Study Design
This research employed a prepost within-subject experimental design where the same
blind study participants conducted crossings in both a pretest before and a posttest after
treatment installation. In each treatment instance, a period of several weeks elapsed between
treatment installation and conducting of the posttest data collection. This was to permit
drivers to acclimate to the presence of the treatment. The within-subject experimental
design optimized the statistical power of the analysis, which was critical given the high degree
of within- and between-subject variability inherent in the crossing task.
During the experiments, blind participants were familiarized with the intersection geom-
etry and traffic patterns by a certified orientation and mobility (O&M) specialist, who also
accompanied the participants during all crossing trials. Subjects were instructed to cross
when ready and were not prompted by the O&M instructor as to when to do so. Participants
were thoroughly briefed on all aspects of the study. Each participant provided his/her signed
informed consent prior to the study. All aspects of the study were reviewed and approved by
the Institutional Review Board (IRB) of Western Michigan University as well as a National
Academy of Science (NAS) Institutional Review Board.
Analysis Framework
A critical contribution of this research project was the formulation and application of an
analysis framework that could be used to quantitatively describe the crossing performance of
individual pedestrians as well as to quantify the accessibility impacts of the tested crossing
treatments. The analysis framework devised by this project identifies four distinct criteria,
which in isolation describe specific components of the crossing task, and which in combina-
tion provide an operational assessment of the accessibility of a site.
1. Crossing opportunity criterion
Are there sufficient crossing opportunities in the form of yields or crossable gaps?
2. Crossing opportunity utilization criterion
Are the crossing opportunities detected and/or utilized by the pedestrian?
3. Delay criterion
Is a crossing opportunity taken within a reasonable time?
4. Safety criterion
Does the crossing interaction occur without a significant degree of risk?
The interpretations of the italicized terms (sufficient, reasonable, and significant) in the
analysis framework are discussed, but are ultimately subject to policy considerations. This
report presents more detailed definitions of what constitutes a yield or crossable gap and
offers discussion on how varying levels of delay and safety performance may be interpreted.
The research team makes no claim that the current empirical framework for what is consid-
ered to be accessible is the final answer to this question. It does, however, represent a frame-
work that was consistently applied to the evaluation of the crossing performances generated
by these treatments and to the simulation and statistical modeling based upon these cross-
ing data. And equally important, it represents a measurement and data collection approach
that can be carried out by current practitioners and future researchers in the field.
Field Study Results
The empirical field studies were performed at two signalized intersection approaches with
channelized right turn lanes, at three single-lane roundabouts, and at two multilane round-
about approaches. The results are reported separately by facility type.
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Channelized Turn Lanes
This research provided evidence that channelized turn lane locations can be very challeng-
ing to cross for a blind pedestrian. While the mainline crossing locations at signalized inter-
sections often have pedestrian signals supplemented with APS, the channelized right turn
lanes are typically not signalized. Turning speeds in channelized lanes are a function of the
facility design and often can approach 2030 mph at the crosswalk. At the same time, driver
attention is often diverted to the task of looking for gaps in the cross-street traffic in prepa-
ration for the downstream merge task. Observations at the test locations gave evidence that
yielding behavior was very low, in the range of 15%, and that driver speeds were higher dur-
ing signal phases where no conflicting downstream traffic was expected. Given the frequency
of these types of facilities across the United States, the research team has identified a con-
cern for accessibility that may even go beyond that of the (presently less frequent) round-
about installations. More research is strongly recommended in this area to work toward
national accessibility guidelines for channelized turn lanes.
At the tested location, the pretest pedestrian performance measures were characterized by
mean pedestrian delays of 25 s to cross the single lane of traffic. The 85th percentile delay
was 40 s. The crossing was further characterized by high risk. On average, the accompany-
ing O&M instructor had to intervene (i.e., pull back the blind participant) during 5.6% and
9.4% of the crossings at the two CTL locations, respectively. These interventions took place
when the O&M instructor perceived there to be a high risk of a pedestrianvehicle collision.
In addition to high speeds and low yielding rates on the order of 15% to 18%, the cross-
ing difficulty was attributed to high ambient noise levels from adjacent traffic at the main
intersection and a difficulty to discern turning vehicles from through traffic.
The CTL crossing treatments included a pedestrian-actuated, flashing-yellow beacon and
on-pavement sound strips that resulted in an audible "clack" noise when traversed by a turn-
lane vehicle. The beacons were intended to increase driver yielding, while the sound strips
were intended to improve the audible information of turning-versus-through vehicles. The
evenly spaced sound strips further sent different sound patterns for a vehicle traveling at
constant speed compared to one that was decelerating in potential preparation for a yield.
The sound strips were tested in isolation as well as in combination with the beacon. The
results showed that the sound strip in isolation resulted in a significant decrease in O&M
interventions, from 9.4% to 2.9%. A light reduction in average delay from 26.2 s to 18.5 s
was not statistically significant. The combination beacon and sound-strip treatments signif-
icantly reduced O&M interventions from 5.6% to 1.4% and decreased overall pedestrian
crossing delay from an average 23.4 s to 12.2 s to cross one lane of traffic. The treatment
effect was attributed to a slight increase in driver yielding (15.2% to 22.0%), but mostly to
an increased rate of utilization of yield and gap crossing opportunities. The interventions
observed following installation of the treatments suggest that risky pedestrian crossings were
not totally eliminated by the installation of the pedestrian-actuated flashers and/or the
surface-mounted sound-strip treatments. It could therefore be argued that accessibility was
improved but not totally achieved with these CTL treatments.
The team concludes that signalized treatments may need to be considered at channelized
turn-lane sites, where the combination of high traffic volumes and speeds results in a risky
and high-delay crossing environment. While no low-volume and low-speed turn lanes were
tested, the team recommends that the sound strip and beacon treatment combination be
further evaluated at other locations due to its low cost and degree of control. Since field tests
suggested that high vehicle speeds contributed to the high incidence of unsafe crossings at
the tested location, geometric designs and treatments intended to reduce vehicular speed,
such as traffic calming designs, raised crosswalks, pork-chop island design, narrow lane
width, small curve radii, and the absence of an acceleration lane may further decrease the
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likelihood of unsafe crossing judgment by pedestrians who are blind. In short, there are a
number of yet-to-be-researched CTL treatments that have the potential to improve CTL
accessibility.
Single-Lane Roundabouts
This research concludes that while some blind research participants had difficulties crossing
single-lane roundabouts in a safe manner, these sites appear not to pose crossing difficulties
that are beyond those experienced by many blind travelers at similar signalized intersections.
The accessibility of single-lane roundabouts seems to be critically linked to:
· Low vehicle speeds at the crosswalk, where reduced vehicle speeds are the result of good
geometric design as opposed to driver willingness to reduce speeds due to the possibility
of encountering a pedestrian;
· The willingness of a majority of drivers to yield to pedestrians;
· Properly installed detectable warning surfaces at all transition points between sidewalk
and the street, including the pedestrian splitter island; and
· Availability of O&M instruction customized to roundabout crossings to explain to pedes-
trians the intersection geometry and the expected traffic patterns at the crossing.
Field studies performed as part of this project evaluated three single-lane roundabouts with
varying geometries and traffic volumes. At two of the three roundabouts, the majority of blind
participants were able to identify and utilize crossing opportunities within approximately 11 s
of average delay per pedestrian for crossing one leg of the roundabout (entry or exit). At the
third single-lane roundabout, average delay was 25 s, with many blind participants experi-
encing even longer delays to cross one lane of traffic. Interestingly, this high-delay round-
about was characterized by low traffic volumes (9,900 vehicles per day) and low yielding rates
(approximately 6%), which resulted in pedestrians waiting for "all-quiet" periods to cross.
The rate of O&M interventions at this low volume roundabout was also low at 0.8%.
A slightly higher intervention rate (1.4%) was observed at one of the other, lower-delay,
single-lane roundabouts. At the third single-lane roundabout, the rate of interventions was
3.9%, which raises concerns that some attributes of single-lane roundabouts decrease acces-
sibility. Traffic volumes at this roundabout were higher (more than 15,000 vehicles per day),
but a yielding rate of 33% resulted in a relatively low average delay of around 11 s per pedes-
trian per leg.
There were some blind travelers at all three single-lane roundabouts, however, who expe-
rienced higher delays in crossing (up to an average 74 s per leg over all crossing attempts) and
some who experienced higher than average intervention rates. The research team was directed
by the study panel to not evaluate any treatments at single-lane roundabouts.
There remains concern over the accessibility of single-lane roundabouts with vehicle
speeds higher than those observed at the data collection sites, with higher traffic volumes,
and with a lower likelihood of drivers yielding to pedestrians. Future research should target
such sites and investigate treatments that are geared towards reducing speeds and increas-
ing yielding behavior.
Two-Lane Roundabouts
This research confirmed that two-lane roundabouts are challenging and not accessible with-
out the provision of additional crossing treatments or without a drastic change toward an
increase in likelihood of drivers voluntarily yielding to pedestrians. The crossing difficulties
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are attributed to generally higher speeds and traffic volumes compared to single-lane facilities.
Higher driver speeds appear to be inversely related to the likelihood of drivers yielding to
pedestrians, and are further associated with a higher risk of pedestrian injury in the event of
a collision. Multilane crossings further carry the added risk of multiple-threat situations,
where a yielding vehicle in the near lane may visually and auditorily mask the presence of a
vehicle in the far lane, relative to the position of the waiting pedestrian.
Prior to treatment installation, the two-lane roundabout in this study showed average
O&M intervention rates on the order of 2.4% to 2.8% of crossings and average delays of
16 to 17 s to cross just one of the two legs (entry or exit) of the roundabout. While these
statistics shouldn't be generalized across all two-lane roundabouts, the team believes that
the crossing performance could be even worse at higher-volume facilities and at round-
abouts with three-lane approaches, which should be the focus of future research.
Two treatments were tested at the two-lane roundabout location, both of which resulted
in notable improvements over the pretest condition. The tested treatments were a pedestrian
hybrid beacon (PHB, also known as a HAWK signal) and a raised crosswalk. Both resulted in
statistically significant decreases in pedestrian delay and crossing risk at the test locations.
The raised crosswalk treatment reduced average pedestrian delay from 17.0 s to 8.0 s. The
PHB reduced delay from 16.0 s to 5.8 s on average for crossing two lanes of traffic. The inter-
vention rates at the two studied crosswalks dropped from 2.8% of trials and 2.4% of trials
prior to installation to zero after installation of each of these treatments. The team concludes
that without treatment in place, pedestrians who are blind may be exposed to an unaccept-
able level of risk at two-lane roundabouts. It is further concluded that the risk level appeared
acceptable after either of the tested treatments was installed at this site and under prevailing
(traffic) conditions. It is unclear if and how crossing performance would change with higher
traffic volumes or at a site with different geometry.
The team was surprised that the intervention rate for both treatments was zero, as it was
anticipated that the raised crosswalk would not yield as great a risk reduction as the PHB.
Field notes from a team observer indicate that there were eight risky multiple threat crossings
at the raised crosswalk that did not actually result in interventions. No such events were
recorded at the PHB. Additional research at other locations and with other individuals is nec-
essary to determine whether there is in fact no difference in risk between these two treatments.
Interpretation
Applications to Other Sites
The report presents two approaches for extending the research results to other locations.
The first approach is based on statistical modeling of pedestrian delay as a function of behav-
ioral attributes of pedestrians and drivers. The second approach is based on traffic micro-
simulation, where the same behavioral attributes can be used to simulate different behaviors
of pedestrians and drivers. Both approaches are considered preliminary at this point, and a
more extensive application is necessary to build confidence in the validity of these approaches.
Pedestrian Delay Models
Separate delay models are developed for single-lane roundabouts, two-lane roundabouts,
and channelized turn lanes. All three models use natural-log transformed explanatory vari-
ables that predict a decrease in delay with an increase in yielding, the availability of crossable
gaps (i.e., less traffic), and the rate of utilization of yield and gap crossing opportunities. The
models predict greater delay for channelized turn lanes than for single-lane roundabouts,
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assuming the same traffic patterns and pedestrian behavior. Similarly, delays are greater at
two-lane roundabouts than at the other sites, assuming that traffic patterns and user behav-
ior are fixed.
The resulting delay models are statistically significant and produce good estimates of
pedestrian delay that match observed field data. The underlying probability terms can be
estimated from field observations for other sites or can be estimated from the technical
literature and traffic flow theory concepts. The resulting models allow the analyst to dis-
tinguish delay encountered at channelized turn lanes, single-lane roundabouts, and two-
lane roundabouts. They further allow the analyst to represent the impact of pedestrian
crossing treatments on delay.
Simulation
The NCHRP Project 3-78A analysis framework uses the principles of gap and yield avail-
ability, the rate of utilization of both types of crossing opportunities, and other performance
measures that quantify the level of delay and risk experienced by a pedestrian. This report
illustrates that these measures fit within the realm of microsimulation software, which thus
represents a second approach for extending the results of this project beyond the observed
sample of sites.
The availability parameters represent characteristics of the traffic stream and are a func-
tion of traffic volumes, speed, and driver behavior. The utilization parameters are pedestrian
behavior attributes that describe a pedestrian's ability and willingness to cross in a yield or
gap situation. These factors represent various inputs into a simulation tool and also become
sensitivity parameters that can be used to explore changes in driver behavior, pedestrian skill
level, or even the installation of a pedestrian crossing treatment. It is demonstrated in this
report that input parameter changes in a simulation model result in the hypothesized effects
on pedestrian delay and risk measures.
Additionally, the report presents a detailed evaluation of different pedestrian signaliza-
tion options for single-lane and two-lane roundabouts that considers various crossing
geometries and signal phasing strategies, including a comparison of a traditional pedestrian-
actuated signal and the PHB that was also field tested in this research. The analysis showed
that the impacts of a roundabout pedestrian signal on vehicle operations can be mitigated
by using two-stage phasing, a separation of the exit portion of the crosswalk from the circu-
lating lane, and the use of the PHB phasing strategy.
Policy Implications
The U.S. Access Board Draft Public Rights-of-Way Accessibility Guidelines (PROWAG)
specify a pedestrian-actuated signal at two-lane roundabout crosswalks with pedestrian
facilities. However, the Americans with Disabilities Act (ADA) allows equivalent facilitation
in all implementations of requirements. Consequently, other treatments that provide equiv-
alent accessibility are acceptable. This is to allow for improvements in technology, develop-
ments in materials or research, or the implementation of new ideas and information. It is up
to the designer and/or constructing jurisdiction to provide justification for their installation
decisions in the case of an ADA complaint. The team believes that there is some confusion in
the interpretation of these standards, in that some may fail to recognize the inherent differ-
ence in civil rights laws and engineering standards.
While the current draft requirements focus on two-lane crossings at roundabouts and
CTLs as well as treatments that provide information about the crosswalk location such as
landscaping or barriers, there is still a responsibility to design and build all facilities to be
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"accessible to and usable by" pedestrians with disabilities (DOJ 1990). The data presented
in the present work strongly argues against the belief that all single-lane roundabouts are
created equal. While one of the studied sites showed generally low delay and risk, a sec-
ond site had high pedestrian risk, while the third exhibited high delays. There was high
inter-participant variability, which makes any broad conclusions about the accessibility of
a particular roundabout type difficult. Further, single-lane channelized turn lane crossings
proved very challenging to most of the blind study participants, and additional treatments
are necessary. The accessibility of this CTL site was not fully established with the low cost and
low degree of control treatments tested in this project, and increased attention therefore
needs to be given to this access issue in addition to the national attention on the accessibil-
ity of roundabout crossings.
Wayfinding Challenges
This research was primarily focused on the aspect of accessibility that is related to the
actual decision of when to initialize a crossing. As discussed earlier in this report, the full
accessibility of a crossing involves three other critical tasks: (a) the task of locating the cross-
walk, (b) the task of aligning to cross, and (c) the task of maintaining alignment during
crossing. Several treatments are available that can assist in these important accessibility tasks,
and these should be evaluated in future research.
However, even today anecdotal evidence suggests that certain facility design elements
and supplementary treatments can be valuable assets to blind travelers. Design elements
that help pedestrians locate the crosswalk include landscaping along the curb (except at the
crosswalk) and the presence of a curb ramp at the crosswalk. This landscaping also may pro-
vide a clue to blind pedestrians that the intersection is a roundabout. The PROWAG and
other U.S. Access Board resources provide additional detail on these and other wayfinding
and alignment treatments. The reader is encouraged to refer to those references for further
information.
Future Research Needs
This report makes specific recommendations for research in continuation of the work of
this research project. With the imminent adoption of the PROWAG, it is necessary to further
explore crossing solutions for blind travelers and work toward building a sample size of obser-
vations that is appropriate for making policy decisions on a national level. Future research is
expected to be facilitated by numerous municipalities and agencies that are already taking the
initiative and proceeding with treatment installations. This research can capitalize on the
momentum of the ongoing national accessibility debate and existing treatment installations
and therefore can be performed with much greater efficiency. The specific areas of future
research identified in this report are as follows:
1. More testing and treatment evaluation at channelized turn lane sites, with particular
emphasis on treatments with a red signal display for drivers, as well as traffic calming treat-
ments that more drastically increase yielding.
2. Additional treatment testing at two-lane roundabouts to increase sample size and build
confidence in treatment effectiveness, with emphasis on treatments with a red signal dis-
play and more low-cost traffic calming treatments such as raised crosswalks.
3. Supplemental data for single-lane roundabouts to improve our understanding of the rela-
tionship of design and traffic volumes to accessibility, and exploration of treatment needs
at high-volume and high-speed designs.
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4. Development of improved measures to quantify pedestrian risk that provide a more com-
plete picture than O&M interventions
5. Exploration of education and training measures to assist blind travelers in successfully
navigating unknown geometries at roundabouts and channelized turn-lane intersections
6. Added focus on the auditory environment at the crosswalk, its relation to vehicular traf-
fic volumes, and its effect on the ability of a blind pedestrian to make sound crossing deci-
sions, with consideration of the increased frequency of quiet and hybrid vehicles in the
traffic stream.
7. Evaluation of new roundabout designs, the potential value in relocating pedestrian cross-
walks upstream/downstream of the circulatory traffic lane, and the inclusion of effective
speed-calming design treatments between the point where traffic exits the roundabout
and a downstream pedestrian crossing location.
While the in-depth evaluation with many participants at each site as performed through
NCHRP Project 3-78A was necessary to establish relationships at sufficient statistical power,
future research may benefit from revised research designs that sacrifice some statistical
power for a greater sample size across more test sites. In working toward broadly applicable
guidelines for pedestrian accessibility across the United States, research focused on breadth
rather than depth should receive higher priority.
