| Low speed urban streets are designed to provide both access and mobility, and accommodate multiple road users, such as bicyclists and pedestrians. Generally, low operating speeds are desired on these facilities to achieve the intended functions and improve overall safety. However, speeds on these facilities often exceed the intended design speeds.; Current design speed approach for low speed urban streets often results in operating speeds higher than design speeds and may therefore be inappropriate for urban street environments. The design speed approach incorporates a significant safety factor to account for worst case scenarios, such as wet pavements and older drivers. As a result, the selected design speed may be lower than the speed a driver is likely to expect. Therefore, it is not surprising that during good weather conditions, general drivers feel comfortable traveling at speeds higher than the roadway's design speeds. To overcome the shortfalls of the design speed approach, several previous studies have proposed a new performance-based design procedure with the incorporation of operating speeds. Under this procedure, the geometric parameters of the roadways are selected based on their influences on the desired operating speeds. This approach provides design consistency checks of existing highways as well as proposed preliminary alignment designs with a feedback loop. However, the operating speed approach requires clear linkage between the relationships of operating speeds and various road characteristics. Although numerous studies have developed operating speed models, most of the previous research concentrated on rural two-lane highways. In contrast, highway designers and planners have very little quantifiable information regarding the influence of low-speed urban street environments on drivers' speeds.; This dissertation investigated the relationship between drivers' speed choices and their associated low speed urban roadway environments by analyzing second-by-second in-vehicle GPS data from over 200 randomly selected vehicles in the Atlanta, Georgia area. This dissertation develops and calibrates operating speed models for low-speed urban streets based on roadway environments, including alignment, cross-section characteristics, roadside features, and adjacent land uses. The research results can help highway designers and planners to design and evaluate proposed low-speed urban roadway designs and improvements. |
