Currently motorcyclists take advantage of their mobility by slipping in and out of stuck traffic. A separate lane for motorcyclists would fascilitate this possibility and lower the danger of present weaving in and out of traffic. And it would pave the way as a first step for innovative vehicles of the type you describe to prove their economic worth.

What if the vehicles could also link together, so you could use the smaller part for 1 or 2 people and hook them together for the family or with a friends car for road trips?

I seen a tech show review one once. I believe it was called "The Sparrow"

I'm a big fan of the two-tandem car idea--also discussed in http://www.whynot.net/ideas/4019

but the Corbin Sparrow was only a one-seater. http://en.wikipedia.org/wiki/Corbin_Sparrow

The two-tandem electric that I think best typifies this post is called the "Tango" and isn't really available yet. But it's electric.

http://www.commutercars.com/

Looks really cool, but with that price, it will never make it.

Plenty of other (gas)two-tandem cars have been made and sold, including the Messerschmitt, the Pulse. The Ecomobile ane the Carver are currently being sold too. Various wheel-counts, too.

http://en.wikipedia.org/wiki/Messerschmitt_KR200http://www.autocycles.org/http://www.ecomobile.com/http://www.carver-worldwide.com/Home/Index.asp?nc=1

I don't really know why one has never caught on, though. Any guess?

Something similar to check out. Go to bombardier.com and check out the new 3 wheeled vehicle.

Bombardier

http://www.popularmechanics.com/blogs/automotive_news/4212570.html

interesting, but not enclosed. Still equals a motorcyle in terms of transit--too cold, too wet, too windy.