Growing awareness of environmental and public health problems associated with motorized transportation has led to a recent effort to promote nonmotorized modes of travel. Previous studies have shown that facility design plays a large role in encouraging bicycling. With the aim of defining the roadway configurations that lead to safe motorist and bicyclist behavior, this research examines the impact of design elements, including the type and width of the bicycle facility, the presence of adjacent motor vehicle traffic, parking turnover rate, land use, and the type of motorist-bicyclist interaction. Observational studies conducted at 48 sites in three large Texas cities characterize bicyclist and motorist behavior through lateral position measurements and instances of motorist encroachment on an adjacent lane. These observations were used to build two multivariate regression models and allowed for direct site-to-site comparisons. Notable results include the observation that bicycle lanes create a safer and more predictable riding environment relative to wide outside lanes, and that the provision of a buffer between parked cars and bicycle lanes is the only reliable method for ensuring that bicyclists do not put themselves at risk of being hit by opening car doors.