These are gatherings of cyclists who ride together, en masse, taking control of the road space. Critical mass is pure inspiration, for those who ride and have seen their streets temporarily transformed from a transport sewer into a peaceful space for the living. Around thirty towns and cities in Britain have a regular ride, and the number is growing. Spontaneity, flexibility and freedom are what it is about. It is not just a demonstration, but people riding their bikes together, each with their own motivation.