The Skoda Streetcar (in Portland) is 66 feet long

Streetcar and Bike, 10th and Washington, Miles Hochstein, Portland Ground.

and can move 30 people seated and 127 standing.

66 feet of roadway can accommodate about 4 cars, carrying typically no more than 2 people each. (Note that the Mini, a "small" car, is 12 feet long.)

Which is more efficient and effective use of the vital streetspace that Len Sullivan cares for so deeply?

Also see, in terms of utilizing rights of way, "Rapid Streetcar:Rescaling Design and Cost for More Affordable Light Rail Transit," from Light Rail Now.

See for yourself. If you can't go to Portland, at the very least you can look at Portland Streetcar photos on Flickr.