Many busy intersections are congested during rush-hour because there is a long line of cars waiting to turn left. The line of cars causes backup and slows down traffic in the adjacent lane. As people try to turn left during the signal's yellow and red phase, the crossing traffic waits at their green light until the intersection clears. This delay creates more backup.

This can significantly slow down bus routes as well; a bus waiting to turn left at a busy intersection may be stuck for up to 3 minutes. (for example, see the intersection of Centinela and Washington Blvd)

If these busy intersections had additional yellow and green left-turn signals, traffic could pass through more efficiently. I strongly suggest a review of signals on all of Los Angeles' boulevards and major avenues -- especially ones on which buses make left turns.

Update: LADOT website claims left-turn arrows are one of their most popular requests - but I haven't found out how to request it:

http://ladot.lacity.org/tf_Left-Turn_Arrows.htm