or some people, the Critical Mass monthly bicycle ride is a protest against car culture. For others, it’s a simple joyride through Boston and Cambridge neighborhoods. For everyone, it is a celebration of bicycling. Whatever the reason, Critical Mass attracts dozens of cyclists who take to the streets of Boston on the last Friday night of every month. While the guerilla group is only loosely organized and its members avoid labeling themselves as activists, it promotes alternatives to automobiles and tries to increase awareness of cyclists’ needs. Members are known to bring noisemakers along for the ride, and share a drink or two after. All are welcome, but BYOB (bring your own bike). Moravek