Operating-Speed Model for Low-Speed Urban Tangent Streets Based on In-Vehicle Global Positioning System Data

Abstract

Low-speed urban streets are designed to provide both access and mobility and to accommodate multiple road users, such as bicyclists and pedestrians. However, speeds on these facilities often exceed the intended operating speeds, as well as their design speeds. Several studies have indicated that the design speed concept, as implemented in the roadway design process in the United States, does not guarantee a consistent alignment promoting uniform operating speeds less than design speeds. A promising design approach to overcome these apparent shortfalls of the design speed approach is a performance-based design procedure with the incorporation of operating speeds. However, this approach requires a clear understanding of the relationships between operating speeds and various road environments. Although numerous previous studies have developed operating-speed models, most of these studies have concentrated on high-speed, rural two-lane highways. In contrast, highway designers and planners have little information about the influence of low-speed urban street environments on drivers’ speeds. This study investigated the relationship between drivers’ speed choices and their associated low-speed urban roadway environments by analyzing second-by-second in-vehicle global positioning system (GPS) data from more than 200 randomly selected vehicles in the Atlanta, Georgia, area. The authors developed operating-speed models for low-speed urban street segments on the bases of roadway alignment, cross-section characteristics, roadside features, and adjacent land uses. The results of this research effort can help highway designers and planners better understand expected operating speeds when they design and evaluate low-speed urban roadways.