Protected Left Turns - Beginning or End of Cycle?

[jeffandnicole]

The opinions are probably going to be very similar to this thread from a few years ago, along with several other conversations within other topics: https://www.aaroads.com/forum/index.php?topic=13659.msg2012296#msg2012296

[Flint1979]

Michigan's is a mixture of both and I don't know which one it should be.

Chicago has them before the through traffic gets their green.

[1995hoo]

As a practical matter, I prefer leading lefts at permissive lights because that's what's normal around here and it causes confusion when there's a lagging left arrow at a permissive light. People don't expect it and the "pull out into the intersection to wait" crowd are usually unaware that the green arrow has come on (to be fair, the one intersection I can think of near where I live that uses that sequencing has the light in a spot that's hard to see if you pull out into the box to wait, so that's a design issue as much as it is a driver issue).

The other reason I'm not a huge fan of lagging lefts is that there are a few in the District of Columbia (14th and G NW comes to mind) and they almost always cause problems with pedestrians. People see the light turn in one direction and they start to walk because they think it's going red both ways, but it isn't. Again, this is just as much a sign of bad pedestrian behavior (refusing to wait for the "Walk" signal) as it is anything else, but it is a real problem.

Now, as I said before, both of those points are based on practical considerations. If instead I were addressing the issue in a vacuum, say if I were asked how the lights should be configured in a brand-new city, I'd agree with the idea that it depends on the overall street layout. What other lights are nearby? What sequence is most effective in ensuring tailbacks don't extend far enough to cause box-blocking at the next block back? That's going to vary from place to place. I've certainly seen non-permissive lagging lefts that work OK (Charlottesville has several of them). The only real negative I see with those is that in this part of the country they're far less common than leading lefts, such that people aren't expecting them and you wind up with wasted green time because people don't move when the light turns. But again, part of that is driver error in not paying attention, although it'd be nice if our traffic lights had the phase that tells you you're about to get a green light like you see in the UK, among other places.

[Revive 755]

Chicago has them before the through traffic gets their green.

There are (were?) at least a couple that were lagging in Chicago.  One was at Cicero and Lawrence.


My preference is whatever allows the best coordination.

There's also the very rare middle of the cycle left turns to consider.  Laporte Road at Silhay Road in Valparaiso, Indiana used to have this.  IIRC WB lefts and thrus would go, then WB and EB lefts, and then the EB left and EB thrus would go.