Proxy Methods for Quantifying Pedestrian Accessibility at Complex Street Crossings

This research intends to introduce three reproducible proxy methodologies to understand the contributing factors and assess safety and accessibility of pedestrians (who are blind). These methodologies are; 1) a field observational study of pedestrian-vehicle conflicts, 2) a controlled field study of driver yielding behavior to pedestrians, and 3) a controlled laboratory study of the effect of different treatments at roundabout approaches to increase driver yielding rate. Each of three proxy methods for evaluating pedestrian accessibility offers its own advantages and shortcomings. This research demonstrates that each of the three methods can be applied to the study of pedestrian access to modern roundabouts, targeting different aspects of accessibility with an emphasis on access to pedestrians who are blind.;The first proxy method is the Conflict-based Assessment of Pedestrian Safety (CAPS) framework. The CAPS method is based on measurements of microscopic traffic variables and relates pedestrian crossing decisions (interaction between a pedestrian and a vehicle) to advanced measurements of vehicle dynamics to estimate lane-by-lane conflicts. The CAPS framework is applied to a study of blind pedestrian crossings at a multi-lane roundabout, and it is calibrated using optimization techniques in the form of three clustering methodologies (K-mode, K-means and K-median). The clustering algorithms assisted in reducing the number of variables for CAPS from five to three: Time-to-collision, deceleration rate and lane condition. However the methodology requires more data collection for calibration and error reduction.;The second proxy method aims to identify the contributing factors affecting the likelihood of a driver yielding to pedestrians at two-lane roundabouts approaches. The method contributes a controlled field data collection protocol that provides event-level data on driver decisions, and is evaluated using a logistic regression approach. The logistic regression models developed from the collected data show that the likelihood of a driver yielding at the entry leg of roundabouts is higher than at the exit. Drivers tend to yield to pedestrians carrying a white cane more often than to sighted pedestrians. Drivers traveling in the far lane, relative to pedestrian location, have a lower probability of yielding to a pedestrian. As the speed increases, the probability of driver yielding decreases. At the exit leg of the roundabout, drivers turning right from the adjacent lane have a lower propensity of yielding than drivers coming from other directions. The research enables researchers to explicitly account for these factors contributing to (low) yielding at multilane roundabouts, thus target specific strategies that may improve yielding and thereby accessibility.;The third methodology is a controlled laboratory study with a driving simulator, which offers a cost-effective opportunity to test various treatments that might affect the driver yielding behavior, as a pre-screening to field installation and testing. It also enables researchers test driver behavior by not only controlling the pedestrian, but also the type of environment and treatment that the driver is exposed to. The treatments evaluated by the simulator are stop bar and crosswalk re-location away from the beginning of exit leg, and two types of beacons: a Pedestrian Hybrid Beacon (PHB) and a Rectangular Rapid Flashing Beacon (RRFB). The study shows that the installation of any kind of beacon (PHB or RRFB) with or without crosswalk relocation, increases driver yielding rates significantly. The results of using an eye tracker on drivers to track their gaze pattern while exiting the roundabout shows that having a beacon installed with crosswalk relocation increases drivers' attention both on the beacon and the pedestrian along the road. The study suggests the need for a more in-depth field test of crosswalk relocation at multi-lane roundabouts.;The controlled field study and controlled laboratory study are both effective in helping understand the factors that increase crossing opportunities for pedestrians and ultimately increases the accessibility of the intersection. However, the field observational study of pedestrian-vehicle interactions and the CAPS framework enables the researcher to quantify the risk level of crossing decisions made by pedestrians. The simulator study is a highly useful approach for screening potential treatment alternatives prior to filed installation of only the most promising options.;Overall, this research described and applied there divers proxy methods for quantifying different aspects of pedestrian accessibility, and illustrated how each method can contribute significantly to the understanding of the complex interaction of drivers and (blind) pedestrians at complex street crossings.