Midwestern Traffic Pattern Mystery

I just returned home from a road trip, feeling pretty smug about having figured out a deep mystery.

Driving around quiet areas of the Midwest, in places with lots of easy parking spots and few traffic jams, I constantly found myself trying to make left turns, but needing to wait for ludicrous lengths of time. The traffic would just keep coming and coming...even though there was, again, really not much of it, all told.

It took me several days to figure out the reason; why it's so much more of an ordeal to make left turns in easy-going suburban Cleveland or Pittsburgh than in the bustling thoroughfares of Queens or Brooklyn. Any guesses? I'll post mine tomorrow.