Richard Long

Development and Implementation of Conflict-Based Assessment of Pedestrian Safety to Evaluate Accessibility of Complex Intersections

This paper describes the development and implementation of the conflict-based assessment of pedestrian safety (CAPS) methodology for the evaluation of pedestrian accessibility at complex intersections. Significant research has explored pedestrian access to modern roundabouts and other complex intersections, and a significant focus has been placed on accessibility for pedestrians who were blind. A majority of these studies relied on actual street crossings by study participants under the supervision of a trained orientation and mobility specialist. These crossing studies quantified risk from a measurement of intervention events, in which the orientation and mobility specialist had to physically stop the participant from crossing. Although such studies provide useful data on the crossing risk at a particular intersection, street crossings can be dangerous to the study participants and are time-consuming and expensive to conduct. The CAPS method emphasizes the use of conflict-based safety factors to quantify risk in a framework compatible with indicator studies. This method relates pedestrian crossing decisions to advanced measurements of vehicle dynamics to estimate lane-by-lane conflicts and identifies the grade of conflict on the basis of a five-criterion rating scale. The CAPS framework was applied to a study of crossings by blind pedestrians at a multilane roundabout. The resulting risk scores were calibrated from the actual orientation and mobility interventions observed during the study. The calibrated CAPS framework correctly matched all (high-risk) orientation and mobility intervention events and further identified other (lower-risk) pedestrian–vehicle conflicts. The CAPS framework provides a more efficient, objective, and consistent safety assessment of pedestrian crossings in a research context, without the need for pedestrians to step into the roadway.

Crossing Solutions at Roundabouts and Channelized Turn Lanes for Pedestrians with Vision Disabilities

This report is intended to provide practitioners with useful information related to establishing safe crossings at roundabouts and channelized turn lanes for pedestrians with vision disabilities. The specific focus areas of the report provide guidance on: identifying under what conditions pedestrians with vision disabilities may experience problems with crossing performance; tying treatment solutions to specific crossing challenges faced by the visually impaired pedestrian population; conducting pedestrian/vehicle studies that help identify performance problems and appropriate treatment strategies; quantifying pedestrian accessibility at a particular crossing; presenting findings from selective field studies performed through this research; developing approaches for extending research findings to other locations; and discussing implications for the practitioner in terms of treatment selection and facility design. The results of this research will be useful to engineers, the accessibility community, policy makers, and the general public to aid in understanding the specific challenges experienced at these facilities by pedestrians with vision disabilities. It is only through the understanding of the components of the crossing task and the particular challenges involved that solutions can be developed, installed, and evaluated appropriately.

Treating lead-contaminated soil by stabilization and solidification

Soil in and near transportation facilities often is contaminated with lead because lead once was used as a base for gasoline and paint. Dealing with contaminated soil is difficult because the toxic material must be treated to protect the public from direct exposure. Stabilization and solidification is a promising technique for protecting the public from toxic materials in soils by decreasing the possibility of human exposure and decreasing the mobility of the contaminant. The results of a laboratory investigation of the feasibility of stabilization and solidification of contaminated soil using cement in combination with various additives are presented. Mobility of lead and other contaminants was measured by dynamic diffusion and compared with the standard test results of the toxic characteristic leaching procedure. Several additives were tried. Apatite and sodium silicate were found to be the most effective in reducing the mobility of the lead. The compacted dry density of the solidified soil had a great effect on the leaching characteristics. The leaching of lead from deteriorated solidified soil was simulated by crushing a sample containing apatite and conducting a dynamic diffusion test on the crushed sample. The diffusion coefficient was used to compare the effect of additives and other treatments.

Blind and Sighted Pedestrians’ Road-Crossing Judgments at a Single-Lane Roundabout

Objective: The aim of this study was to evaluate the relative risk and efficiency of road crossing experienced by blind and sighted pedestrians at a single-lane roundabout with two levels of traffic volume and at two distances from the roundabout. Background: With the rapid spread of modern roundabouts across the United States, their accessibility to blind pedestrians has become an important concern. To date, accessibility research relevant to blind pedestrians has focused on multilane roundabouts, and single-lane roundabouts have been virtually ignored. Method: Blind and sighted participants made judgments about when they would cross a single-lane roundabout with high and low traffic volumes, at exit and entry lanes, and at the actual crosswalks and at locations farther from the roundabout. Results: Relative to sighted participants, blind participants’ judgments about when to cross were more frequently risky, especially when traffic volume was high. Blind participants also were slower to make crossing judgments and accepted fewer crossing opportunities. Both groups made somewhat safer and more efficient judgments at locations farther from the roundabout. Conclusion: Some single-lane roundabouts may pose greater risk to blind pedestrians than to sighted pedestrians, especially when traffic volume is high. Crosswalk location merits further investigation as a design issue. Application: These findings are relevant to transportation planners and engineers who are responsible for the accessibility of public rights-of-way.

Wayfinding Problems for Blind Pedestrians at Noncorner Crosswalks: Novel Solution

To travel independently, pedestrians with visual impairments must be able to locate crosswalks and align accurately for crossing streets. This action is especially challenging where crossings are not located at street corners and cues for locating the crosswalk and aligning to cross in the direction of travel on the crosswalk may be inadequate. This research compared midblock and roundabout crossings with curb ramps and detectable warnings but no other consistent cues for locating the crosswalk and no cues specifically intended to provide alignment and heading information, with the same crossings with the addition of a 24-in.-wide prototype surface of raised bars oriented perpendicular to the direction of travel on the crosswalks. This treatment was installed beside the detectable warnings and extended across the sidewalk. It was hypothesized that this surface would assist with both locating the crosswalk and establishing accurate alignment with the crosswalk. Sixteen participants having little or no vision failed, on average, to locate the crosswalk on the initial approach on 2.4% of their attempts for crosswalks having the guidance surface, while without the guidance surface, participants failed to locate the crosswalk on the initial approach on an average of 17.9% of their crossing attempts. With the guidance surface, participants aligned correctly on average on 77.3% of their trials, while without the surface the rate of correct alignment was 52.1%.