on one-way loops

On Transport has a nice post on the Detroit People Mover, a loop that connects a number of major employment and activity centers in downtown Detroit.  

In a recent post I argued that downtown shuttles aren't of much use unless they're extremely frequent.  The Detroit People Mover doesn't have that problem; it runs every 3-5 minutes.  It has the other common problem of downtown shuttles: it's a big one-way loop.

(Detroit's loop is clockwise, having reversed direction in 2008.  Some one-way loops, like the one at the heart of Melbourne's train system, also reverse direction in the middle of the day.)