i don't think these things would mix well with modern traffic, unless perhaps in very crowded city traffic. similar vehicles would have a use in citys where conventional cars where banned. mobility, parking space, and pollution issues would much improve, and safety issues would be far less (in fact this vehicle would be the bigges player in the field so you'd have to pay attention to everyone else).
the vehicles that comes closest to this would be the BMW C1 scooter
http://en.wikipedia.org/wiki/BMW_C1
not a car and not fully enclosed, but arguably with more or less the same confort level and much improved safety
at the bottom of the wiki page there a link to crash test footage, with a nice comparison to a convetional scooter.
over here these are selling for 2000 to 4000€ used
get's around 78mpg.