Improved Driver Yielding Model for Pedestrian Delay Estimation.

HUNTER, ELIZABETH ELAINE. Improved Driver Yielding Model for Pedestrian Delay Estimation. (Under the direction of Dr. Nagui Rouphail.) The interaction of pedestrians and motorized traffic at unsignalized intersections needs to be further explored to determine the effects on intersection operation and pedestrian safety. Pedestrian crossing delay at unsignalized intersections, specifically midblock crossings, is dependent on the availability of gaps between vehicles and driver yield events. Unsignalized midblock crossings are common in downtown areas and college campuses. The Highway Capacity Manual (HCM) 2010 has made an effort to combine pedestrian gap acceptance and driver yielding behavior to predict pedestrian delay, but the methodology has not been calibrated by field observations. Mean yield rates for several crossing treatments, for a few sites, are provided. Mixed-priority pedestrian delay models for single-lane roundabouts address the interaction where some drivers yield to pedestrians and some pedestrians accept gaps. But to date, no predictive model exists to estimate yield probability based on sitespecific attributes. Validation and improvement of the HCM 2010 and mixed-priority pedestrian delay estimation methods is the major objective of this research. Research consisted of using three widely used methods to determine critical gap, specifically, HCM calculation, maximum likelihood estimation (MLE), and the graphical method. A regression model to predict motorist yielding rate based on site characteristics was developed and results were then compared with observed rates. The two delay estimation methods, three critical gap methods, and observed and predicted yielding rates resulted in twelve values for estimated average pedestrian delay per site. These estimates were compared with field observed delay. Data collected at 27 sites in North Carolina, Florida, and Alabama contributed to validation and improvement of the HCM and the mixed-priority pedestrian delay models. Both pedestrian delay estimation methods use pedestrian critical gap values and motorist yield rates. For maximum likelihood estimation and the graphical method, sites were grouped by crosswalk length. Longer critical gap values were typically seen at the sites with longer crosswalks. Multiple linear regression was used to develop a model that could be implemented in the HCM to predict motorist yield rate from site characteristics. Model development consisted of both categorical and numerical data. The final motorist yielding model included onor off-campus, whether the site was in Florida, oneor two-way, and crossing width as the independent variables. This model had an overall adjusted R value of 0.7261. The model was found to be more accurate at predicting high and low motorist yielding rates than it was at mid-level motorist yielding rates. Over half of the sites were accurate within 15%. Results appeared more accurate when the sites were grouped by common characteristics, such as onor off-campus and oneor two-way traffic. It is recommended that this model be used when field data is unavailable. An effort was made to validate the HCM pedestrian delay method, but even after using three different critical gap estimation methods and two different yield values, the estimates never matched the observed values. Average pedestrian delay was underestimated using the HCM method. The mixed-priority model with the observed yield encounter probability and the critical gap from the graphical method showed the most accurate results. A trendline for the observed delay against the predicted delay from this method had an R value of 0.894. This model was designed to apply to any pedestrian population, where perfect utilization is assumed for sighted pedestrians. It was determined that an additional conversion factor of 0.68 could be applied to more accurately predict the average pedestrian delay. Further research in additional states should be performed in order to validate the findings of this research. It is recommended that the mixed-priority pedestrian delay model, with an adjustment factor, be used over the HCM method. © Copyright 2014 by Elizabeth Elaine Hunter