Can flashing yellow arrow (4 section heads) show lead/lag protected lefts?

[johndoe]

Maybe it's too early in the morning for my brain, but I'm wondering if flashing yellow arrows could communicate leading / lagging peotected status.  Drivers who arrive during the permissive left (FYA) aren't clear if their left leads or lags.  If it lags, the driver may have eased past the stop line and will be fine as the signal goes from FYA to green arrow.  But if it leads, the driver who may have eased past the stop line will "sneak" through yellow - not safe.

If there were a way to communicate "green arrow coming next" or (more importantly) "green arrow NOT coming next" drivers may not "sneak" on yellow and it could be safer.  Ideally this would be done with the 4 section head already in place.  Hmm, thoughts?  Have places tried something like this?

[UCFKnights]

Maybe it's too early in the morning for my brain, but I'm wondering if flashing yellow arrows could communicate leading / lagging peotected status.  Drivers who arrive during the permissive left (FYA) aren't clear if their left leads or lags.  If it lags, the driver may have eased past the stop line and will be fine as the signal goes from FYA to green arrow.  But if it leads, the driver who may have eased past the stop line will "sneak" through yellow - not safe.

If there were a way to communicate "green arrow coming next" or (more importantly) "green arrow NOT coming next" drivers may not "sneak" on yellow and it could be safer.  Ideally this would be done with the 4 section head already in place.  Hmm, thoughts?  Have places tried something like this?

The entire point of the FYA is to make it safe to always enter the intersection on the FYA. There is no yellow trap anymore that would make it unsafe to enter the intersection when the FYA cycle ends. When your FYA switches to solid yellow and then red, the opposing traffic must have the same happening, so its safe to clear the intersection at that point.

[ran4sh]

In other words, yes. In fact the lead/lag split cycle with permissive left turns is the main reason for fya to exist as an indication, because before fya if you wanted lead/lag you needed to use protected-only phasing.

[johndoe]

The entire point of the FYA is to make it safe to always enter the intersection on the FYA. There is no yellow trap anymore that would make it unsafe to enter the intersection when the FYA cycle ends. When your FYA switches to solid yellow and then red, the opposing traffic must have the same happening, so its safe to clear the intersection at that point.

Agreed, except that switching to solid yellow isn't TOTALLY ideal- both the left and the opposing through may assume the other driver will stop and they need to clear intersection.  Don't get me wrong, I'm in favor of FYA and get why they exist-just wondering if that extra information would help drivers.

[roadfro]

In other words, yes. In fact the lead/lag split cycle with permissive left turns is the main reason for fya to exist as an indication, because before fya if you wanted lead/lag you needed to use protected-only phasing.

Not true. You could have had lead/lag PPLT with 5-section displays using Dallas Phasing, which was the whole reason that scheme was created in the first place. This was used in a few places besides Dallas (the Las Vegas area had a few installations). But ISTR Dallas Phasing required special programming logic in the signal controller to get the circular indications to display properly, so it was not easy to implement everywhere. The advent and proliferation of FYA signals and controllers that can accommodate it makes lead/lag PPLT a more readily-available option.

The entire point of the FYA is to make it safe to always enter the intersection on the FYA. There is no yellow trap anymore that would make it unsafe to enter the intersection when the FYA cycle ends. When your FYA switches to solid yellow and then red, the opposing traffic must have the same happening, so its safe to clear the intersection at that point.

Agreed, except that switching to solid yellow isn't TOTALLY ideal- both the left and the opposing through may assume the other driver will stop and they need to clear intersection.  Don't get me wrong, I'm in favor of FYA and get why they exist-just wondering if that extra information would help drivers.

That's no different than permissive left on green without a separate left turn phase. If the left turn driver creeps out into the intersection and the light turns yellow, there's no visible cue to what the opposing through signal indication is. Rules of the road dictate the turning driver still must yield to the opposing through traffic before proceeding.

[Henry]

IIRC, when a green arrow is also in use and that cycle ends, the steady yellow arrow lights up first two heads above, then it drops back to the flashing yellow in between. After that, the steady yellow arrow lights up once more, and finally, the red arrow shows. However, I'm sure there are inconsistencies that exist where a green arrow will light up once in a while, or not at all.

[Big John]

IIRC, when a green arrow is also in use and that cycle ends, the steady yellow arrow lights up first two heads above, then it drops back to the flashing yellow in between. After that, the steady yellow arrow lights up once more, and finally, the red arrow shows. However, I'm sure there are inconsistencies that exist where a green arrow will light up once in a while, or not at all.

Aound here it momentarily goes to red before going to flashing yellow.

[ran4sh]

In other words, yes. In fact the lead/lag split cycle with permissive left turns is the main reason for fya to exist as an indication, because before fya if you wanted lead/lag you needed to use protected-only phasing.

Not true. You could have had lead/lag PPLT with 5-section displays using Dallas Phasing, which was the whole reason that scheme was created in the first place. This was used in a few places besides Dallas (the Las Vegas area had a few installations). But ISTR Dallas Phasing required special programming logic in the signal controller to get the circular indications to display properly, so it was not easy to implement everywhere. The advent and proliferation of FYA signals and controllers that can accommodate it makes lead/lag PPLT a more readily-available option.

This is correct, I knew Dallas phasing was an option but I didn't think it was actually a permanent part of the MUTCD. But apparently it was in the 2003 MUTCD and then was banned in the 2009 MUTCD with fya being the preferred option by that time.

[US 89]

In other words, yes. In fact the lead/lag split cycle with permissive left turns is the main reason for fya to exist as an indication, because before fya if you wanted lead/lag you needed to use protected-only phasing.

Not true. You could have had lead/lag PPLT with 5-section displays using Dallas Phasing, which was the whole reason that scheme was created in the first place. This was used in a few places besides Dallas (the Las Vegas area had a few installations). But ISTR Dallas Phasing required special programming logic in the signal controller to get the circular indications to display properly, so it was not easy to implement everywhere. The advent and proliferation of FYA signals and controllers that can accommodate it makes lead/lag PPLT a more readily-available option.

This is correct, I knew Dallas phasing was an option but I didn't think it was actually a permanent part of the MUTCD. But apparently it was in the 2003 MUTCD and then was banned in the 2009 MUTCD with fya being the preferred option by that time.

How much Dallas phasing is left in the DFW metroplex? There was some left in 2017 but it seemed like they were in the process of converting a bunch of them to FYAs, and I didn't see any when I briefly passed through in 2022.

[johndoe]

That's no different than permissive left on green without a separate left turn phase. If the left turn driver creeps out into the intersection and the light turns yellow, there's no visible cue to what the opposing through signal indication is. Rules of the road dictate the turning driver still must yield to the opposing through traffic before proceeding.

True - I suppose some drivers looking at a three-section head would assume (maybe wrong if bimodal) it's permissive-only.  I was imagining something like a second flashing arrow during the FYA to mean "don't worry, you're about to get your protected turn".

[jakeroot]

Instead of using a signal indication, use pavement markings. If left turns are lagging, and "creeping out" is to be encouraged, paint a waiting box for traffic to sit in.

Here in Japan, all protected turns are lagging. Each direction starts with a green light. Traffic going straight moves on, while traffic turning right pulls out into the waiting box. If there is a gap, traffic can turn through, otherwise the right turn green arrow comes on at the end. Because there are no dedicated signals for right-turning traffic, both directions get green arrows of the same length, which is kind of annoying at rush hour, when a busy right turn is opposite a very quiet right turn, but it's the only way to prevent yellow trap.

Not all right turns have protected green arrows. Waiting boxes are still used everywhere, and the Japanese are always taught to wait in these boxes. Intersections with no green arrow usually have a longer all-red (like 3-5 seconds). Here is an example of where there is no green arrow: https://goo.gl/maps/gjdLqHN1zyfchGTs5

Here is an example of a large intersection in Okinawa. Traffic waits at the dashed white line, and then a green arrow moves them through at the end if no gap is found:


真玉橋南 (Madanbashi South JCT) by Jacob Root, on Flickr

If it's worth anything, the lanes are all 10 feet wide; the speed limit for wider road is 60 km/h and the narrower road is 40 km/h. I think the wider road, the Naha-Higashi Bypass, will eventually have an expressway built in the median (elevated, overhead).

[US 89]

I wish we had those waiting boxes in the US, or at least an indication to use some amount of the intersection to wait to turn left. It goes a long way towards improving left-turn throughput. In Salt Lake, most people would pull maybe a quarter of the way into the intersection waiting for a gap to turn through, which guarantees at least one or two cars will turn every cycle even without a protected phase. Nobody seems to do that in Atlanta or Tallahassee.

[ran4sh]

I wonder how well those Japanese waiting boxes would work with American truck traffic.

I'm also not in favor of sacrificing safety for throughput. If an intersection doesn't have flashing yellow arrows or protected-only signals, then traffic shouldn't wait in the intersection to turn left (due to the yellow trap hazard).

[jakeroot]

I wish we had those waiting boxes in the US, or at least an indication to use some amount of the intersection to wait to turn left. It goes a long way towards improving left-turn throughput. In Salt Lake, most people would pull maybe a quarter of the way into the intersection waiting for a gap to turn through, which guarantees at least one or two cars will turn every cycle even without a protected phase. Nobody seems to do that in Atlanta or Tallahassee.

I've noticed it's a geographical thing. When I visit family in Indianapolis, spend time around the Chicago area, etc...always pulling forward to turn left. In Seattle, it's more common than not, but not 100% of traffic. But other areas, very uncommon. I wish they were more common too, if only to cut down on "where do I wait" concerns from people, especially at larger, more ambiguous intersections. It's really important here in Japan, as double right turns (those across traffic) are almost always permissive, so the waiting boxes help both turning lanes not interfere with one another. If the US used this kind of phasing more often with double left turns, waiting boxes would be very helpful.

[jakeroot]

I wonder how well those Japanese waiting boxes would work with American truck traffic.

It works the same as any other double turn, the waiting boxes merely require traffic to complete roughly a third of the turn ahead of time, waiting for a gap for the other two-thirds.

Here in Japan, while trucks are all cabover, so easier to maneuver, it doesn't affect things much. Very long trucks usually use the outside lane, and turn out further than the guidance lines would typically suggest, though not so much as to interfere with the opposing right turn box.

I'm also not in favor of sacrificing safety for throughput. If an intersection doesn't have flashing yellow arrows or protected-only signals, then traffic shouldn't wait in the intersection to turn left (due to the yellow trap hazard).

Well, just don't program yellow trap; most places in the US forbid lead/lag with 5-section signals specifically to prevent yellow trap. Here in Japan, we avoid it by having the green arrows come on at the end simultaneous with one another.

[johndoe]

Thanks for sharing the boxes, Jake.  I'm sure the maintenance crews love that   I know some of the more "unique" markings don't get refreshed as often just because of manpower struggles - I imagine other parts of the country / world are similar.  Is the "blue" always reserved for yielding in intersections for their system?  One other question about their system: do they often use lower signal heads or add supplementary heads?  I kinda struck out on street view examples, maybe you have a good example?  If the yield line were far enough out in the intersection, it'd be hard to see "up" enough to see the signal heads in some cases.  Here MUTCD says 40' min from signal head to stop line.

I guess always lagging (or leading) solves the uncertainty issue, but there is a reason leading and lagging are both used... if you want efficient two-way coordination with most intersection spacings, you must lead some and lag others.  Some even vary by time of day. 

[jakeroot]

Sorry for the very long post ... I have been learning a lot since I moved here.

Thanks for sharing the boxes, Jake.  I'm sure the maintenance crews love that   I know some of the more "unique" markings don't get refreshed as often just because of manpower struggles - I imagine other parts of the country / world are similar.  Is the "blue" always reserved for yielding in intersections for their system?

The maintenance thing is an issue, for sure. The boxes at this major intersection are almost completely gone. But my guess is that they'll be through to paint them soon enough, they are constantly doing road maintenance, and the crews are often enormous for even a small project (presumably to get it done faster).

The painted blue boxes are kind of new, I've seen them at some newer intersections but they're still not very common. I haven't quite worked out when they are supposed to be used vs when they are not used, but they are used for both through and turning traffic depending on the situation. Red boxes are often used to help guide traffic towards a major place, like an airport, but also sometimes approaching an intersection or when there is a tight turn. Green is often used when there is an expressway entrance (tolled or un-tolled), like here. Sometimes, they just throw the whole book at a stretch of roadway, throwing in some "slow down" edge markings for good measure.

One other question about their system: do they often use lower signal heads or add supplementary heads?  I kinda struck out on street view examples, maybe you have a good example?  If the yield line were far enough out in the intersection, it'd be hard to see "up" enough to see the signal heads in some cases.  Here MUTCD says 40' min from signal head to stop line.

I guess always lagging (or leading) solves the uncertainty issue, but there is a reason leading and lagging are both used... if you want efficient two-way coordination with most intersection spacings, you must lead some and lag others.  Some even vary by time of day.

I would like for Japan to figure this out at some point. Their current system of signalizing intersections is ... not great. It's true, many intersections, especially smaller ones, have only one signal head. I thought it was more common to have two, but this is not the case. While it's become more common to two or more signals, they usually opt for one far-left and one near-right; far-right is more common at larger/newer intersections, but many still lack it. This does require you to peek over your shoulder to check on the status of the light. Sometimes the car up front doesn't notice, so a car at the rear will beep if no one moves. Extra signals around corners are decently common, thankfully (vertical, near-side signal as an example).

There are no separate signal heads for turns, so a typical protected-only intersection will have signals like this, where there is a red orb being displayed, but green arrows for straight and left turns (green arrow left turn still requires yielding to pedestrians ... genius), followed by a red orb with a right turn green arrow for the protected right turn phase. If you're keeping track, yes, that means the green orb is not used at all, except during off-peak hours when the green orb takes over for the straight and left arrows, allowing permissive right turns. The yellow orb is used for ending both green arrows and green orbs, as they do not use bimodal arrows. Protected-only operation does allow for lead-lag, but in practice I don't recall seeing this. Plus, protected-only intersections are very rare so it doesn't surprise me they haven't taken the time to be more creative with phasing.

What's really strange: Japan does not allow green arrows to be displayed for simultaneous with green orbs, or at least hasn't carved out a meaning for it yet. At a T-intersection, during the right turn off the top of the T, the signal simply stays green with no indication that oncoming traffic has a red light. The only indication is the pedestrian signal going red (thankfully ped signals are almost always tied to through traffic, except at all-way walk intersections); a green arrow below the green orb would be so, so helpful.

[Troubleshooter]

We have two FYA signals here that give either leading or lagging green arrows depending on what traffic is actually there.

[jakeroot]

We have two FYA signals here that give either leading or lagging green arrows depending on what traffic is actually there.

Where is "here"? You don't have a location listed.

[Troubleshooter]

We have two FYA signals here that give either leading or lagging green arrows depending on what traffic is actually there.

Where is "here"? You don't have a location listed.

Bloomington IN

I thought I entered that when I restarted. It asked me..

[kphoger]

I thought I entered that when I restarted. It asked me..

You can confirm what we see by looking at your profile.

[Troubleshooter]

In other words, yes. In fact the lead/lag split cycle with permissive left turns is the main reason for fya to exist as an indication, because before fya if you wanted lead/lag you needed to use protected-only phasing.

Not true. You could have had lead/lag PPLT with 5-section displays using Dallas Phasing, which was the whole reason that scheme was created in the first place. This was used in a few places besides Dallas (the Las Vegas area had a few installations). But ISTR Dallas Phasing required special programming logic in the signal controller to get the circular indications to display properly, so it was not easy to implement everywhere. The advent and proliferation of FYA signals and controllers that can accommodate it makes lead/lag PPLT a more readily-available option.

This is correct, I knew Dallas phasing was an option but I didn't think it was actually a permanent part of the MUTCD. But apparently it was in the 2003 MUTCD and then was banned in the 2009 MUTCD with fya being the preferred option by that time.

How much Dallas phasing is left in the DFW metroplex? There was some left in 2017 but it seemed like they were in the process of converting a bunch of them to FYAs, and I didn't see any when I briefly passed through in 2022.

Dallas phasing can remain for the useful life of the equipment. No new Dallas Phasing intersections are allowed.

I wish we had those waiting boxes in the US, or at least an indication to use some amount of the intersection to wait to turn left. It goes a long way towards improving left-turn throughput. In Salt Lake, most people would pull maybe a quarter of the way into the intersection waiting for a gap to turn through, which guarantees at least one or two cars will turn every cycle even without a protected phase. Nobody seems to do that in Atlanta or Tallahassee.

I've noticed it's a geographical thing. When I visit family in Indianapolis, spend time around the Chicago area, etc...always pulling forward to turn left. In Seattle, it's more common than not, but not 100% of traffic. But other areas, very uncommon. I wish they were more common too, if only to cut down on "where do I wait" concerns from people, especially at larger, more ambiguous intersections. It's really important here in Japan, as double right turns (those across traffic) are almost always permissive, so the waiting boxes help both turning lanes not interfere with one another. If the US used this kind of phasing more often with double left turns, waiting boxes would be very helpful.

It depends on whether drivers have been caught in yellow trap in the area. Those who have been caught don't enter the intersection.

Also some states make it illegal to enter an intersection unless you can immediately leave it.

I thought I entered that when I restarted. It asked me..

You can confirm what we see by looking at your profile.

Done!

[Troubleshooter]

Fixed your quote string for you.  Be sure to use the [Preview] button when doing complicated quoting.

In other words, yes. In fact the lead/lag split cycle with permissive left turns is the main reason for fya to exist as an indication, because before fya if you wanted lead/lag you needed to use protected-only phasing.

Not true. You could have had lead/lag PPLT with 5-section displays using Dallas Phasing, which was the whole reason that scheme was created in the first place. This was used in a few places besides Dallas (the Las Vegas area had a few installations). But ISTR Dallas Phasing required special programming logic in the signal controller to get the circular indications to display properly, so it was not easy to implement everywhere. The advent and proliferation of FYA signals and controllers that can accommodate it makes lead/lag PPLT a more readily-available option.

This is correct, I knew Dallas phasing was an option but I didn't think it was actually a permanent part of the MUTCD. But apparently it was in the 2003 MUTCD and then was banned in the 2009 MUTCD with fya being the preferred option by that time.

How much Dallas phasing is left in the DFW metroplex? There was some left in 2017 but it seemed like they were in the process of converting a bunch of them to FYAs, and I didn't see any when I briefly passed through in 2022.

Dallas phasing can remain for the useful life of the equipment. No new Dallas Phasing intersections are allowed.

I wish we had those waiting boxes in the US, or at least an indication to use some amount of the intersection to wait to turn left. It goes a long way towards improving left-turn throughput. In Salt Lake, most people would pull maybe a quarter of the way into the intersection waiting for a gap to turn through, which guarantees at least one or two cars will turn every cycle even without a protected phase. Nobody seems to do that in Atlanta or Tallahassee.

I've noticed it's a geographical thing. When I visit family in Indianapolis, spend time around the Chicago area, etc...always pulling forward to turn left. In Seattle, it's more common than not, but not 100% of traffic. But other areas, very uncommon. I wish they were more common too, if only to cut down on "where do I wait" concerns from people, especially at larger, more ambiguous intersections. It's really important here in Japan, as double right turns (those across traffic) are almost always permissive, so the waiting boxes help both turning lanes not interfere with one another. If the US used this kind of phasing more often with double left turns, waiting boxes would be very helpful.

It depends on whether drivers have been caught in yellow trap in the area. Those who have been caught don't enter the intersection.

Also some states make it illegal to enter an intersection unless you can immediately leave it.

I thought I entered that when I restarted. It asked me..

You can confirm what we see by looking at your profile.

Done!

While I was fixing it.

[kphoger]

While I was fixing it.

Post removed!

[jakeroot]

I wish we had those waiting boxes in the US, or at least an indication to use some amount of the intersection to wait to turn left. It goes a long way towards improving left-turn throughput. In Salt Lake, most people would pull maybe a quarter of the way into the intersection waiting for a gap to turn through, which guarantees at least one or two cars will turn every cycle even without a protected phase. Nobody seems to do that in Atlanta or Tallahassee.

I've noticed it's a geographical thing. When I visit family in Indianapolis, spend time around the Chicago area, etc...always pulling forward to turn left. In Seattle, it's more common than not, but not 100% of traffic. But other areas, very uncommon. I wish they were more common too, if only to cut down on "where do I wait" concerns from people, especially at larger, more ambiguous intersections. It's really important here in Japan, as double right turns (those across traffic) are almost always permissive, so the waiting boxes help both turning lanes not interfere with one another. If the US used this kind of phasing more often with double left turns, waiting boxes would be very helpful.

It depends on whether drivers have been caught in yellow trap in the area. Those who have been caught don't enter the intersection.

Also some states make it illegal to enter an intersection unless you can immediately leave it.

Yellow trap? That doesn't exist anymore. Any remaining examples are mistakes or left over from when it was OK, and should be removed.

I believe Oregon is one of those states, but I've not seen it truly affect drivers' propensity to wait in the junction. Like, it's not illegal at all in WA to be in the intersection on red, as long as you clear it. But maybe a fifth of drivers refuse to wait in the junction, and would happily miss three light cycles all to avoid being in the junction on red for a few seconds...lunacy. They would have a heart attack here in Japan.