Crossing Solutions at Roundabouts and Channelized Turn Lanes for Pedestrians with Vision Disabilities (2011) / Chapter Skim
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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.
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The crossing task at channelized right turn lanes and modern roundabouts is challenging 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.
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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 combination provide an operational assessment of the accessibility of a site.
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In addition to high speeds and low yielding rates on the order of 15% to 18%, the crossing 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 turnlane vehicle.
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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 pedestrians the intersection geometry and the expected traffic patterns at the crossing.
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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.
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Additionally, the report presents a detailed evaluation of different pedestrian signalization options for single-lane and two-lane roundabouts that considers various crossing geometries and signal phasing strategies, including a comparison of a traditional pedestrianactuated 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 circulating lane, and the use of the PHB phasing strategy.
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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 display and more low-cost traffic calming treatments such as raised crosswalks.
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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.
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