Which type of vehicle is specifically propelled by human power and typically has two wheels?

The bicycle is a vehicle that is specifically designed to be propelled by human power, utilizing the physical effort of the rider. It typically features two wheels aligned in a single line, which is a defining characteristic of bicycles. Riders operate the bicycle through pedals, which convert their energy into forward motion. This mode of transportation is not only eco-friendly but also promotes physical fitness, making it unique compared to the other options.

Motorcycles, while also two-wheeled vehicles, are powered by an engine and therefore do not depend on human power for propulsion. A tricycle, though it may be human-powered, consists of three wheels rather than two. Lastly, a Segway is a two-wheeled vehicle that relies on electric power and sensors to operate, distinguishing it from the human-powered design of a bicycle. Thus, a bicycle is the only option among the provided choices that correctly fits the description given.