Lag Left Turn Signals
Lag Left Turn Signals
(OP)
Just a general question a driver for you traffic engineers from a Manufacturing Engineer. The city of Tucson, AZ instituted "Lag Left" turn signals a number of years ago. The story was that it would move more vehicles thru the left turn lanes since some would get a chance to turn even before the left green arrow came on. Tucson has stuck with it but I haven't heard or seen any one else pick it up. Any insight on whether this was a good move, bad move or had no effect?





RE: Lag Left Turn Signals
Lagging lefts can be useful in some circumstances, less helpful in others. If there are never natural gaps in traffic, lags may increase delay to left turning vehicles. However a lead left can't service vehicles that aren't already there at the beginning of the green.
It's hard to generalize about traffic because every intersection has unique characteristics. Sometimes corridor considerations (maximizing thru greenbands) take precedence over servicing turns.
RE: Lag Left Turn Signals