In recent years the number of kick scooters, hand cycles, wheelchairs, and other emerging user types has increased on roads and shared use trails. The Federal Highway Administration recognized that because the American Association of State Highway and Transportation Officials' (AASHTO's) design recommendations are based on the characteristics of bicyclists, they may not adequately accommodate other users. Further, some emerging user groups have been petitioning state legislatures throughout the United States for legal access to public roads. Consequently, determining the operating and safety characteristics of these emerging users has become important for the safe accommodation of all nonmotorized users of the transportation system. Some of the findings of research undertaken to examine the characteristics of bicyclists and emerging users are reported. Three "Ride for Science" data collection events were conducted to obtain the physical dimensions, turning capabilities, acceleration, speed, lateral operating space, and stopping sight distance of trail users. Results show that there is great diversity in the operating characteristics of various road and trail user types. AASHTO's design bicycle length of 6 ft and width of 30 in. were adequate for the majority of observed users. However, bicycle trailers and recumbent bicycles exceeded the design length. Power wheelchairs exceeded the design width. The recommended two-way trail width of 10 ft gave most users traveling single file in opposite directions enough room to pass each other, though some only barely. Results of this research will be valuable in either updating or developing new design guidelines for road and shared use path design to better accommodate emerging user groups.