Examining Bicycle and Motorized Vehicle Speeds and Their Relationships in the Context of Urban Roadways

Abstract

This thesis presents a compilation of papers exploring passenger car and bicycle speeds through their interactions with each other and with urban roadway factors.First, following a concern raised in part of the traffic literature that a large mode shift toward bicycling may cause travel time delays and potentially exacerbate congestion instead of alleviate it unless bicycle lanes are installed, an empirical study detailing how the presence of bicycles on urban roads without bicycle lanes may affect passenger car speeds is presented. Pneumatic tube data from six predominantly low speed, low volume roads in Portland, Oregon were utilized to identify observations of passenger cars (class two vehicles) belonging to one of two vehicle following scenarios. In scenario (i), a passenger car was directly preceded by a bicycle (class one vehicle), and in scenario (ii), a passenger car was directly preceded by another passenger car. Speed distributions were examined, and the mean, the 50th, and the 85th percentile speeds of scenario (i) and scenario (ii) vehicles for both peak-hour and 24-hour traffic were compared using t-tests and confidence intervals. A few statistically significant differences between scenario (i) and scenario (ii) were found, but the actual differences in speed were generally on the order of one mile per hour or less. Thus, from a practical perspective, the presence of bicycles on these roads without bicycle lanes was deemed to have negligible effects on passenger car speeds.Following the results of the initial study, a second study was conducted to address limitations in the initial study regarding the homogeneity of site characteristics. This second study also expanded the research to explore how oncoming (opposing direction)