With a bicycle, I can be a vehicle, I can be a pedestrian, and I can be a train. I can assert myself among cars, making them yield; I can ride among pedestrians without causing them angst; I can ride alongside a train and, assuming the train makes frequent stops, I can reach the next town almost as quickly.
You might say I'm just bragging about being an unusually strong cyclist, but I can tell you I've ridden behind Danish mums who I'm sure would beat me in a time-trial. And while I'm skilled enough to ride among walkers, you would not want me on your bike polo team. Don't give me a job as bike messenger either: I'm hardly the world's most adept vehicular cyclist. I'm as strong and skilled as most people would be, if they were raised in a built environment that reaped the full potential of cycling, as a kind of vehicular transport, a kind of walking, and a kind of moving from town to town.
Designers have to stop putting bikes into a box, with their limited and limiting expectation as to how most cyclists are going to ride. Some will always ride fast, some always with aggression, and some will always ride slow. Most though, will morph between states at will. Designers need to go back and watch the Amazing Chan and the Chan Clan, and take special note of their shapeshifting van.