Protected Left Turn Signal vs. Doghouse vs. Yellow Trap

[traffic light guy]

I get that FYA signals improve traffic flow, but wouldn't saftey be more important? I've even seen FYA signals that lack green. Here's anoter thing, doghouses are not going extinct, they're still used at extremely small intersections, hec, I've even seen videos of FYA doghouses.

[jakeroot]

Regarding permissive lefts, are there any scenarios where the throughput is significantly higher than using a protected turn?

There's three scenarios: fully permissive, protected/permissive, and full protected. The first probably has the lowest throughput, as only two cars could typically turn (after the red light pops up) during a phase where oncoming traffic takes up the entire phase. Second would probably be fully protected, since any gaps in oncoming traffic plus the end (all red phase) could not be utilised for additional turns. Highest is certainly protected/permissive phasing, since it allows the same number of cars through during the protected phase plus any cars that can turn in gaps and at the end.

I will say that FYAs probably have higher throughput than doghouses, because doghouses cannot incorporate lead/lag phasing which can improve overall throughput along a corridor. FYAs can work along lead/lag corridors, which allows maximum flexibility.

As I pointed out previously, Denmark has quite a lot of permissive left turns, as does the UK. Denmark even has quite a few which allow two left turn lanes to yield.

[Revive 755]

Regarding permissive lefts, are there any scenarios where the throughput is significantly higher than using a protected turn?

Has to be some out there where the high volume direction differs between the AM and PM peaks.

I get that FYA signals improve traffic flow, but wouldn't saftey be more important? I've even seen FYA signals that lack green.

Nothing wrong with having a 3-Section FYA head with no green.  If anything, it's nice to have on a corridor with most of the other intersections having 4-Section FYA heads as I can see from a distance that left turns are allowed at an upcoming intersection.

Here's anoter thing, doghouses are not going extinct, they're still used at extremely small intersections, hec, I've even seen videos of FYA doghouses.

More likely they will stay for intersection that have shared right turn heads with a right turn overlap.  If an intersection has a dedicated left turn lane and there are not any overhead utility conflicts and/or historic district restrictions on the use of overhead signals, there's usually no reason a FYA head or a 3-Section protected only head could not be used.

[Henry]

I'm much more comfortable going through protected lefts than a doghouse or FYA. At a doghouse, I will turn when an arrow is on, but when there's no arrow showing, then it's pretty much a crapshoot regarding when to make that left. And FYAs are much more complicated than that, seeing that they use the same function as firehouse signals, with flashing yellows in place of the normal greens.

[jakeroot]

I'm much more comfortable going through protected lefts than a doghouse or FYA. At a doghouse, I will turn when an arrow is on, but when there's no arrow showing, then it's pretty much a crapshoot regarding when to make that left. And FYAs are much more complicated than that, seeing that they use the same function as firehouse signals, with flashing yellows in place of the normal greens.

Do you also have trouble turning left at intersections without signals? Just yield and go.

[jeffandnicole]

I'm much more comfortable going through protected lefts than a doghouse or FYA. At a doghouse, I will turn when an arrow is on, but when there's no arrow showing, then it's pretty much a crapshoot regarding when to make that left.

When traffic is clear?

What do you do if there's no cross traffic to trigger the light? 

[bzakharin]

What I find annoying is when there is no left arrow of any sort when each direction gets a dedicated green, meaning turning traffic has nothing to yield to ever, but you have to know the intersection to be sure this is the case.

There is one intersection that does this near where I live. Would it kill them to build a doghouse where the left arrow is always on together with a green ball? Especially since cross traffic gets a green *right* arrow when the traffic coming from the right gets the green phase. Same situation, isn't it? Right on red is already permitted after a stop, so a green arrow eliminates the stop. Left on green is permitted after stop, so why no green arrow to eliminate the stop? I still hesitate before turning there sometimes thinking "what if I'm misremembering or they reconfigured the light?"

[jeffandnicole]

What I find annoying is when there is no left arrow of any sort when each direction gets a dedicated green, meaning turning traffic has nothing to yield to ever, but you have to know the intersection to be sure this is the case.

There is one intersection that does this near where I live. Would it kill them to build a doghouse where the left arrow is always on together with a green ball? Especially since cross traffic gets a green *right* arrow when the traffic coming from the right gets the green phase. Same situation, isn't it? Right on red is already permitted after a stop, so a green arrow eliminates the stop. Left on green is permitted after stop, so why no green arrow to eliminate the stop? I still hesitate before turning there sometimes thinking "what if I'm misremembering or they reconfigured the light?"

Split phasing without informing motorists that they have the only green is definitely a situation rather unique to New Jersey.  I'm sure there's occasional instances of this elsewhere, but not in the frequency as found in NJ.

The state has gotten better at it, adding the green arrow to signals when they are doing various construction work at the intersections where it exists.  But there's many intersections where you just have to know the other side still has the red.

As far as redoing the light to eliminate the split phasing, that was done near me.  And without any notification at all.  So motorists frequently were just proceeding to turn left on their green ball, while opposing traffic, which used to never have a green ball at the same time, now did.  Many skid marks were the result of people slamming on their brakes.  I'm still a little hesitant sometimes here, hoping other motorists won't suddenly turn in front of me!

[jakeroot]

I'm sure there's occasional instances of this elsewhere, but not in the frequency as found in NJ.

Definitely not something I run into very often, but I knew of two within about ten minutes of each other. Both in Pierce County, Wash, and both driveway exits:

Portland Ave @ 112 St (driveway exit has all orb signals): https://goo.gl/jEkij2

Waller Road @ Pioneer Way (exit from warehouse had all orb signals) (since modified): https://goo.gl/hse1dh

[Amtrakprod]

I understand many love Doghouses, but I'm still one for Flashing yellow arrows. I believe they are the safest signal.


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[Amtrakprod]

I swear I've seen this thread before, and I pointed out (as I'm about to again) that "yellow trap" is not a signal, it's a...mistake.

My personal preference for left turns is fully permissive, then FYA, then doghouse/tower, then fully protected.

Yep, Jake is right, I'm the same in that order.


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