Just the reasons you ride, no?
A quote from a blurb about the movement on treehugger.com:
You have heard of slow food; get ready for slow cities. It is an outgrowth of the slow food movement and like it, started in Italy. According to Der Spiegel, "Slow City" advocates argue that small cities should preserve their traditional structures by observing strict rules: cars should be banned from city centers; people should eat only local products and use sustainable energy. In these cities, there's not much point in looking for a supermarket chain or McDonald's.Read the entire article: Slow Cities Spreading Fast.