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proof that it is inaccessible. Accessibility must be evaluated in patterns, including volumes, gap distributions, and vehicle
terms of direct observation that a facility can be used by all classification.
persons, independent of whether they are actually observed
using it. For the question of the accessibility of complex inter-
Scope of Work
sections to pedestrians who are blind, a conventional engineer-
ing analysis of pedestrian crashes therefore does not provide The objective of this research was to explore through empir-
the necessary information. ical research geometric designs, traffic control devices, and
other treatments that will enable safe crossings at roundabouts
and CTLs for pedestrians who are blind. The results of this
Comparing Roundabouts research also will be useful to engineers, the accessibility com-
and Channelized Turn Lanes munity, policy makers, and the general public to aid in under-
When attempting to cross a CTL or the entry/exit lane of a standing the specific challenges experienced by pedestrians
roundabout, a blind pedestrian must decide, largely on the who are blind at these facilities. It is only through understand-
basis of auditory cues, when it is safe to cross. Both types of ing the components of the crossing task and the particular
facilities share the following common characteristics with challenges involved that solutions can be developed, installed,
respect to the crossing task for blind pedestrians: and evaluated appropriately.
The focus of this research was on people who are blind,
· Use of (typically) unsignalized pedestrian crossings without and therefore the term "blind," rather than "visually impaired,"
an audible device that assists in determining signal status, will be used throughout this document. In this context, peo-
· Potentially high levels of ambient noise associated with ple who are blind are defined as those who have only light-
background traffic at the main intersection or roundabout, perception or less vision and who are therefore unable to
· Free-flowing traffic at the exit portion of the roundabout identify traffic patterns, signs, markings, or signal displays.
crossing and at non-yield-controlled CTLs, The research clearly has implications for other pedestrians
· Challenge of curved vehicle paths that differ from more with vision impairments, which includes those with limited
standard orthogonal intersections, or low vision. But all studies performed through this research
· Ambiguity about vehicle trajectories between through/ involved only pedestrians who are blind according to the
definition above.
circulating and turning/exiting traffic,
·
The guidance in this report is intended to provide practi-
Lack of information identifying the sites as different from
tioners with useful information related to establishing safe
conventional orthogonal intersections, and
crossings at roundabouts and CTLs for pedestrians who are
· Crossings that originate from a refuge island where traffic
blind. The specific focus areas are to provide guidance on:
moves in front of and behind the pedestrian.
· Identifying when a pedestrian crossing problem may be
However, the two types of facilities also exhibit some signif- present,
icant differences that need to be emphasized. Through-vehicle · Tying treatment solutions to specific crossing challenges
(and potentially turning-vehicle) speeds are expected to be faced by the pedestrian population,
higher in the vicinity of a CTL, resulting in an elevated level of · Conducting pedestrian/vehicle studies that help identify
background noise and potentially different behavior in terms appropriate treatment strategies,
of drivers yielding to pedestrians. The difficulty of the auditory · Quantifying the accessibility performance at a particular
discrimination at a CTL will be influenced by a number of crossing,
factors, such as (a) whether the CTL has a dedicated decel- · Presenting findings from selective field studies performed
eration lane and the length of that lane, (b) whether the CTL through this research,
has a dedicated acceleration lane and the length of that lane, · Developing approaches for extending research findings to
(c) the radius of the channelized lane and the associated design other locations, and
speed, and (d) whether vehicles exiting the channelized lane · Discussing implications for the practitioner in terms of
are able to merge with traffic with or without any reduction in treatment selection and facility design.
speed. The last point is principally associated with the pres-
ence and length of a downstream acceleration lane. This report is not intended to provide practitioners with
For roundabout crossings, a range of different roundabout requirements of when to install specific treatments, which is a
geometries exist that affect the crossing task. Roundabouts policy decision. Instead, the team provides useful information
vary in the number of approach lanes, the number of circu- on the concept of accessibility and how to provide improved
latory lanes, the inscribed circle diameter, crossing point dis- crossing environments based on the pedestrian crossing task
tance from circulating traffic, and most importantly traffic at hand.
