mindenpilot wrote:

But what would prevent a design (even low performance/ultra light to start)
that would allow a pilot to fly into an airport, then fold up his wings and
cruise down surface streets at 45mph?

It's been done at least twice. These days, I'd bet the safety equipment required
for highway vehicles in the U.S. would weigh enough to make it absolutely
impossible.

The two approaches I've read about are 1) Have the wings and empennage attach
to the car. The car lands, unhooks the assembly, and leaves it at the airport.
2) Use detachable and folding wings and tailfeathers and trailer them. The EAA
museum at Oshkosh has one of these on display.

These didn't make very good airplanes because of the weight of the automobile
running gear. IIRC, only three of design #2 were built, and I think that was in
the 50s.

George Patterson
He who would distinguish what is true from what is false must have an
adequate understanding of truth and falsehood.