[MetroMPG]

And I have another observation, tangentially related to efficiency:

I got the definite impression that people in the southern states don't signal as reliably as northerners. Anecdote, for sure.

Efficiency effect:

I saw multiple instances of people waiting to exit parking lots who might have made their exit if the approaching car had signalled their intention to turn into said same parking lot. Instead, you get a late-braking, no-signalling entrance, and the departing driver isn't sure what's going on until it's too late to take advantage of the opportunity.