Modular pedal-powered vehicle

Most who have known me for any length of time are aware of this idea: a pedal-powered, solar-boosted, regenerative-braking, lightweight-but-sturdy safe vehicle that you can buy a piece at a time. Young married couple? Just buy the driver-one passengar module. Want to
store stuff, maybe have a basket you can pull off to take through the store? Get the "back boot" or "trunk" - just snaps on. Have a baby, now? Add a rear-seat section. Family of seventeen? Add several rear-seat sections. Any passengers can help pedal; there's another solar panel on each roof, and attaching or detaching sections should be no more difficult or complicated than changing out the seats in a family van. Done properly, these should be much cheaper than conventional cars, and just as safe- given the space-age materials we have now, one should be able to create all the comforts currently available in a luxury car - much more so than previous generations of energy-efficient vehicles.