I want to get a bike...I don't plan on being on many busy roads, but I can envision having to cross a bridge. I'd like to get off a bridge with a lot of car traffic as quickly as possible and mountain bikes have always seemed slow compared to regular thin tired city bikes. If i get a foldable bike with their smaller tires, the idea of crossing a bridge seems even more slow and ridiculous. is there anything to my concerns? any comments? thanks.