Just a quick post about big bikes. I’m talking multiperson bikes here, not tall bikes, which deserve a whole post all to themselves… (someday, someday….).
If a 30-person bike seems like to much, you could learn to make a multi-person thingy (link via Spinopsys), created in Nottingham, England when “people from Nottingham’s Critical Mass and the ASBO bicycle workshop got chatting about the idea of creating some fun alternative bike-based machines.” They are thinking about using the “thingy” as a sound system carrier for their Critical Mass, as well as perhaps turning it into a mobile cafe.
Finally, if neither of the above two options “floats your boat”, you could always just make a Human-powered Car, which I bet has excellent fuel economy.