I don't know if this has been discussed before, but I found what I consiederd to be a dangeroue traffic signal.
The 2 through lanes have the standard R-Y-G signals and the left turn lane has the standard R-Y-G-YA-GA signal.
I suppose this is to keep traffic flowing at a busy intersection, but I noticed after the Protected Left Turn sequence, the Left Turn signal went to Steady Green, while the thru lanes were still Red. Oncoming traffic, however, must have had steady green AND a protected left as traffic was going straight thru as well as turning.
I've only seen this once before and thought it was a dangerous sequence: if the other lanes are Red, but you have Green, wouldn't you assume you had a protected turn? Yes, you should notice there is oncoming traffic, though.
I witnessed an accident today where the person turning left thought she had a protected left on a steady Green and ran into a car passing through the intersection. No one was hurt, fortunately.
Am I wrong in thinking this is a dangerous & confusing signal sequence?
[Modified thread title.]
was there a sign that said "yield to opposite traffic on solid green circle" or similar?
This is a frequent install to be found in Pennsylvania (or at least in my area). Sometimes, there can be 2 thru lanes and 1 turn lane and there will be 1 thru signal and one doghouse signal. Here is an example of the one you explained...
(https://www.aaroads.com/forum/proxy.php?request=http%3A%2F%2Flh6.ggpht.com%2F_ZkmN2RrOJxw%2FSzOhF6jDwTI%2FAAAAAAAASJw%2Fn9-a95QmcD4%2Fs640%2FIMG_1446.JPG&hash=3c79c94c2816852c2dd059e07beffa36a5cd7fa5)
And here is the one with 1 thru and 1 doghouse signal...
http://maps.google.com/maps?hl=en&ie=UTF8&ll=39.9126,-75.435326&spn=0,359.977319&t=h&z=16&layer=c&cbll=39.913072,-75.43701&panoid=-JrCKQs5Y6EFUAf2FXZoiA&cbp=12,70.98,,0,0.83
Quote from: agentsteel53 on January 20, 2010, 09:53:27 PM
was there a sign that said "yield to opposite traffic on solid green circle" or similar?
Should have been, but I don't remember. I'll have to check the photos I took
I'm not sure if I'm misunderstn
Quote from: US71 on January 20, 2010, 09:45:48 PM
I don't know if this has been discussed before, but I found what I consiederd to be a dangeroue traffic signal.
The 2 through lanes have the standard R-Y-G signals and the left turn lane has the standard R-Y-G-YA-GA signal.
I suppose this is to keep traffic flowing at a busy intersection, but I noticed after the Protected Left Turn sequence, the Left Turn signal went to Steady Green, while the thru lanes were still Red. Oncoming traffic, however, must have had steady green AND a protected left as traffic was going straight thru as well as turning.
I've only seen this once before and thought it was a dangerous sequence: if the other lanes are Red, but you have Green, wouldn't you assume you had a protected turn? Yes, you should notice there is oncoming traffic, though.
I witnessed an accident today where the person turning left thought she had a protected left on a steady Green and ran into a car passing through the intersection. No one was hurt, fortunately.
Am I wrong in thinking this is a dangerous & confusing signal sequence?
I'm not sure if I'm misunderstanding your post or not, but, generally, there's a protected phase and a permissive phase at intersections where the five section head (doghouse) signals are installed. If the left lane has a green arrow, then oncoming traffic shouldn't be coming through the intersection on the left turning traffic's protected phase. On a steady green, left turning traffic has to yield to through traffic and right turning traffic, unless right turning traffic has a yield sign.
If the left lane signal was green, through traffic was red and oncoming traffic had a steady green and protected phase, then that's a poorly designed traffic sequence or a glitch in the system.
Be well,
Bryant
It's not a Doghouse, just a standard 5 light signal
R
Y
G
<Y-
<G-
Oh, okay. It's a vertical signal with five lights. Gotcha. The first time I saw one of those was when I first started going to Georgia State. It was at the intersection of Decatur St. SE and Peachtree Center Ave. SE (http://maps.google.com/maps?f=q&source=s_q&hl=en&geocode=&q=Peachtree+Center+Avenue+SE,+Atlanta,+Georgia&sll=39.913077,-75.437&sspn=0.008065,0.01811&ie=UTF8&hq=&hnear=Peachtree+Center+Ave+SE,+Atlanta,+Fulton,+Georgia+30303&ll=33.753148,-84.38766&spn=0.004335,0.009055&t=h&z=17&layer=c&cbll=33.753225,-84.387798&panoid=S5uexNwi0RCkEhXjdfPiqA&cbp=12,119.14,,0,4.08) in Downtown Atlanta.
When the tornado came to Atlanta, the signal was replaced with a doghouse signal.
Be well,
Bryant
I have seen one of those on 21st Street at the ramp to I-20/59 South in Birmingham. It must be a new signal because the casing is black.
I remember two vertical signals with 5 lights at the interchange between US 280 and AL 149 near Mountain Brook. Those have been replaced recently.
Sorry in advance...this is a bit of a technical reply...
Quote from: US71 on January 20, 2010, 10:43:59 PM
It's not a Doghouse, just a standard 5 light signal
Fundamentally, there's no difference between a 5-section cluster ("doghouse") and a 5-section vertical (or horizontal) signal head. Signing and operation are the same.
Most agencies usually use the doghouse on a mast arm or span wire, and use the vertical display for supplemental heads on the far-side pole mount. I've seen some agencies use the vertical display on the mast arm (and Texas frequently uses the horizontal here), but I imagine most like the cluster because it keeps the similar colors aligned to the same height both within the face and relative to adjacent signal heads.
Quote from: US71 on January 20, 2010, 09:45:48 PM
I don't know if this has been discussed before, but I found what I consiederd to be a dangeroue traffic signal.
The 2 through lanes have the standard R-Y-G signals and the left turn lane has the standard R-Y-G-YA-GA signal.
I suppose this is to keep traffic flowing at a busy intersection, but I noticed after the Protected Left Turn sequence, the Left Turn signal went to Steady Green, while the thru lanes were still Red. Oncoming traffic, however, must have had steady green AND a protected left as traffic was going straight thru as well as turning.
I've only seen this once before and thought it was a dangerous sequence: if the other lanes are Red, but you have Green, wouldn't you assume you had a protected turn? Yes, you should notice there is oncoming traffic, though.
I witnessed an accident today where the person turning left thought she had a protected left on a steady Green and ran into a car passing through the intersection. No one was hurt, fortunately.
Am I wrong in thinking this is a dangerous & confusing signal sequence?
By "steady green", I'm assuming you mean a circular green or green ball. If I've interpreted that and the rest of your post correctly, I think what you're describing here is a variant of protective-permissive left turn control known as "Dallas Phasing". This is a signal phasing scheme developed and widely used in Dallas, TX; it has seen a decent amount of use in Las Vegas area as well.
In Dallas Phasing, the circular green of the left turn signal operates independently of the circular greens of the adjacent through signals. This allows the left turn to display a circular green and allow permissive left turns when the opposing direction has a green signal for the through traffic and a green arrow for the left turn. This mode of operation is designed to prevent the "yellow trap" situation that can occur with protective-permissive left turns operated with lead/lag left turn phasing at the intersection. This method of operation does allow for some increased efficiency for the left turn while also allowing lead/lag phasing to be used on the approach, which is often a big help for signal progression on an arterial.
When Dallas Phasing is used, there are a couple conditions that have to be followed in order for it to work properly. First, the 5-section left turn display must be an exclusive signal face, i.e. it must be meant to control the left turn lane only and not the adjacent through lanes. Second, the circular portions of the signal face need to have visibly limiters so that they are only visible to the left turn lane and not the through traffic (usually accomplished with louvers). Third, the standard "Left Turn Yield on Green (symbolic green ball)" (R10-12) sign should be replaced with the "Left Turn Signal (line) Yield on Green (symbolic green ball)" (R10-21) sign. With all these factors in place, the through traffic should not mistake the left turn signal for the through signal.
There is nothing inherently wrong or dangerous about a PPLT display using Dallas Phasing, if the appropriate safeguards are in place. The confusion is more attributable to the fact that it's a fairly unexpected sequence, as a left turning driver typically won't expect to have a circular green when the adjacent through traffic has a circular red. This is likely one of the reasons why Dallas Phasing isn't more widespread.
The greater problem with the accident situation mentioned is that many drivers see a circular green over the left turn lane and automatically assume that they have a protected left turn. This happens frequently with 5-section PPLT displays (whether they run Dallas Phasing or not), but can also happen with a standard 3-section display. The only time you have a protected movement is if an arrow is involved, and not all drivers realize this. This misinterpretation of the circular green in regards to permissive left turns is what prompted a lot of changes to left turn controls in the 2009 MUTCD. Now, 5-section left turn faces can only be used if its circular indications are illuminated simultaneously with whatever is displayed on the adjacent through signal faces. Circular green and yellow indications are no longer allowed in exclusive left turn signal heads...having been deprecated in favor of the flashing yellow arrow display. The flashing yellow arrow display more easily implements the principles of Dallas Phasing, using a 4-section display that doesn't require louvers or other shielding.
^^ Wow, learn something new everyday.
Be well,
Bryant
Sounds like a perfect location for an inline-4 yellow trap signal. Incidentally, Illinois uses the inline-5 signals almost exclusively, as opposed to doghouses.
If I understand Dallas Phasing correctly, a doghouse signal is dedicated to the left turn lane. Protected mode (opposing red) has both the green ball and arrow lit. Permitted mode (opposing green) has just the green arrow lit. Am I correct?
For the sake of clarification, here is a photo of the signal in question:
(https://www.aaroads.com/forum/proxy.php?request=http%3A%2F%2Ffarm5.static.flickr.com%2F4047%2F4292968965_412a54c2e5.jpg&hash=a4581835c8fd4ab1e5e0bb56ae9405c3d862e9c9)
A Left Turn is permitted, but not protected while oncoming WB traffic has steady Green. BUT thru traffic going EB still has Red.
^^ That's screwy. The arrows should be used, not the ball.
Quote from: Brandon on January 21, 2010, 02:00:00 PM
^^ That's screwy. The arrows should be used, not the ball.
But, the turn is
not protected.
This still seems wrong to me, though. It should be a Left Arrow OR Steady green on
all signals... or possibly a Flashing Yellow Arrow (which Fayetteville doesn't have).
Quote from: Brandon on January 21, 2010, 02:00:00 PM
^^ That's screwy. The arrows should be used, not the ball.
That's Dallas phasing, though, as roadfro explained. It's effectively become verboten with the 2009 MUTCD, however. Situations like this were precisely why the flashing-yellow arrow signalface was developed.
Quote from: Michael on January 21, 2010, 12:31:22 PM
If I understand Dallas Phasing correctly, a doghouse signal is dedicated to the left turn lane. Protected mode (opposing red) has both the green ball and arrow lit. Permitted mode (opposing green) has just the green arrow lit. Am I correct?
Not correct on the second count. In permitted mode, the circular green is lit -- as indicated in the photo above.
Quote from: US71 on January 21, 2010, 01:54:12 PM
For the sake of clarification, here is a photo of the signal in question:
(https://www.aaroads.com/forum/proxy.php?request=http%3A%2F%2Ffarm5.static.flickr.com%2F4047%2F4292968965_412a54c2e5.jpg&hash=a4581835c8fd4ab1e5e0bb56ae9405c3d862e9c9)
A Left Turn is permitted, but not protected while oncoming WB traffic has steady Green. BUT thru traffic going EB still has Red.
This would appear to be using Dallas Phasing. They're not using the correct sign, which isn't a big deal. But from what I can tell on the photo, the circular green in the left turn signal head is
not visibility limited from the adjacent through traffic. That is a major safety concern and a violation of the 2003 MUTCD standard for PPLT displays.
I'm working on putting something together to illustrate the differences between Dallas Phasing and other modes. I might have it done this afternoon...
Quote from: rawmustard on January 21, 2010, 02:13:28 PM
That's Dallas phasing, though, as roadfro explained. It's effectively become verboten with the 2009 MUTCD, however. Situations like this were precisely why the flashing-yellow arrow signalface was developed.
That's something I've never seen used in Illinois, Wisconsin, Michigan, or Indiana. Michigan used to use a flashing red ball for the left turn permissive phase (now being replaced with the flashing yellow arrow), but that's it. If I were to look at that signal in the photo, I'd assume there's some malfunction with the signal (based on my experience).
There must be a better way of accomplishing that than with a green ball. How about a flashing red arrow?
Flashing red acts like a stop sign, so this perfectly fits the condition: for left turns, stop, go when clear.
Quote from: Duke87 on January 21, 2010, 04:54:11 PM
There must be a better way of accomplishing that than with a green ball. How about a flashing red arrow?
Flashing red acts like a stop sign, so this perfectly fits the condition: for left turns, stop, go when clear.
sometimes you can take the turn on the fly, though, without needing to come to a complete stop
Same thing I'd think...some sort of malfunction.
If it was intention, it's clearly in violation of the MUTCD, as other posters noted.
And a good candidate for the Flashing Yellow Arrow, if the intention IS to allow left turners to go if clear while the through traffic has the red phase.
Quote from: froggie on January 21, 2010, 05:00:49 PM
If it was intentional, it's clearly in violation of the MUTCD, as other posters noted.
And a good candidate for the Flashing Yellow Arrow, if the intention IS to allow left turners to go if clear while the through traffic has the red phase.
I'm consulting with Gridlock Guru to see if his contacts with AHTD can justify this signal sequence (there are at least 2 others in town I've seen, but never photographed) or if there any plans for a FYA.
For what it's worth, the signal at S. 19th Street and I-35 in Moore, OK does the same thing, but in a doghouse. Baffled me too. Thought about posting here and writing to the Moore DPW... hard to believe this is actually an intentional phasing...
Quote from: Duke87 on January 21, 2010, 04:54:11 PM
There must be a better way of accomplishing that than with a green ball. How about a flashing red arrow?
Flashing red acts like a stop sign, so this perfectly fits the condition: for left turns, stop, go when clear.
There is...flashing yellow arrow.
In addition to flashing yellow arrow displays, the 2009 MUTCD also added provisions for regular use of flashing red arrows. These are to be used in rare circumstances where permitted phasing can be used, but engineering studies/judgment indicates each driver must come to a complete stop before proceeding through the left turn (more severe cases like a sight distance limitation). For 99% of permissive left turn cases, a full stop is not necessary--flashing yellow arrows are better suited for this as they are treated more like a yield situation.
Quote from: US71 on January 21, 2010, 05:17:58 PM
I'm consulting with Gridlock Guru to see if his contacts with AHTD can justify this signal sequence (there are at least 2 others in town I've seen, but never photographed) or if there any plans for a FYA.
The sequence is perfectly valid, according to the 2003 MUTCD. The problem is the lack of louvers in the separate left turn signal head to block the circular green from being seen by the adjacent thru traffic (that part is not compliant).
With revisions in the 2009 MUTCD, this sequence is no longer valid. However, I don't see any compliance dates associated with this. So this can mean that the existing phasing can be retained until the signal is removed, modified or reconstructed--at which time a flashing yellow arrow display would be appropriate.
This took me a little while to finish up, but I hope you all will find it helpful. I've created a short video that explains in a graphic format the differences between the various forms of protected/permitted left turn controls, including Dallas Phasing.
By no means am I a whiz with video capture and online videos, so I hope it works okay. Here it is: http://www.youtube.com/watch?v=KPKjcPI5Sko
^^
Great video. Seeing "Dallas Phasing," as well as the flashing yellow sequence for permissive turns, was pretty cool. I've never seen either of them before. Most of the signals that I've seen in Georgia -- for left turning traffic -- are the "doghouse" signals or the three-section head signals (red arrow/steady red, yellow arrow, green arrow). Additionally, I've not seen too many signals with the "yellow trap," except for the traffic signal on Cleveland Avenue at Jefferson Terrace/S. Fulton Med. Ctr. in East Point, Georgia.
Be well,
Bryant
^ Thanks for the accolade on the video. It was my first effort at doing something like that.
The yellow trap can only show up at PPLT signals using lead/lag for the protected portion of the left turns. Using lead/lag phasing is common when signal coordination is a priority, so you'd have to be in a jurisdiction that focuses heavily on coordination...but such a jurisdiction would (should) have altered the phasing to avoid having the yellow trap occur.
Quote from: roadfro on January 22, 2010, 03:54:27 AM
The yellow trap can only show up at PPLT signals using lead/lag for the protected portion of the left turns. Using lead/lag phasing is common when signal coordination is a priority, so you'd have to be in a jurisdiction that focuses heavily on coordination...but such a jurisdiction would (should) have altered the phasing to avoid having the yellow trap occur.
It can also conceivably occur in situations where a side-street phase is skipped and a serviceable call exists for a lead left-turn leg, although modern controllers should be able to be programmed to prevent this. At least in Michigan, there have been a few instances where on a street crossing a railroad, the yellows would be staggered to where the approach coming towards the track would change before the one going away from the track (basically to match the opposing approach's signal placed in front of the track). In recent years, some of these instances have been fixed as well.
Thanks, roadfro! I sort-of get Dallas Phasing now. I also FINALLY understand yellow trap! :jumping:
Now I have two more questions:
First, using your example, why would you want northbound traffic to stop, allow northbound left turns, and give southbound traffic a green?!
Secondly, why would there be a doghouse signal dedicated to a left-turn lane? It should be shared with a thru head, like the 2009 MUTCD requires. In my opinion, any dedicated left turn signal should either be all arrows, or have an adjacent "LEFT TURN SIGNAL" sign, like this (https://www.aaroads.com/northeast/new_york050/cr-057_nb_at_long_branch_rd.jpg) or this (https://www.aaroads.com/northeast/new_york050/cr-057_nb_at_cr-081.jpg) (light in background of the first photo).
Quote from: rawmustard on January 22, 2010, 08:37:24 AM
It can also conceivably occur in situations where a side-street phase is skipped and a serviceable call exists for a lead left-turn leg, although modern controllers should be able to be programmed to prevent this.
This is true...hadn't thought of that.
My understanding is that when Dallas Phasing was first conceived, there was quite a bit of wrestling involved with signal controllers in order to get the displays to overlap correctly (with the adjacent and opposing thru signals) and not show the yellow trap. Same was true for the flashing yellow arrow situation. Most new signal controllers (last 5 years or so) now have flashing yellow arrow programming built in.
Quote from: Michael on January 22, 2010, 03:19:59 PM
Thanks, roadfro! I sort-of get Dallas Phasing now. I also FINALLY understand yellow trap! :jumping:
I'm glad you found it helpful. When I first learned about the yellow trap in college, I didn't get right away. It partially had to do with the fact that any animation I had seen never showed what was happening with the opposing signal.
Quote from: Michael on January 22, 2010, 03:19:59 PM
First, using your example, why would you want northbound traffic to stop, allow northbound left turns, and give southbound traffic a green?!
A situation like this is most likely to show up during a peak hour timing plan. The arterial is running lead/lag protected lefts in order to help improve signal progression along the corridor.
The geometry of this intersection may be such that the left turn demand cannot be adequately served during the protected only phase. In that case, you want to allow permitted lefts at any time possible. Allowing the NB permitted left to occur while the adjacent thru traffic is stopped gives that left turn more possible chances to complete the turn. In the Dallas Phasing and FYA examples, the NB left had about 12 more seconds to find a gap for a permitted left turn. Given that this time comes at the end of the SB thru movement, it is more likely that there will be gaps in the SB thru traffic thus increasing the chances of being able to make a NB protected left.
Quote from: Michael on January 22, 2010, 03:19:59 PM
Secondly, why would there be a doghouse signal dedicated to a left-turn lane? It should be shared with a thru head, like the 2009 MUTCD requires. In my opinion, any dedicated left turn signal should either be all arrows, or have an adjacent "LEFT TURN SIGNAL" sign, like this (https://www.aaroads.com/northeast/new_york050/cr-057_nb_at_long_branch_rd.jpg) or this (https://www.aaroads.com/northeast/new_york050/cr-057_nb_at_cr-081.jpg) (light in background of the first photo).
One reason to have a separate signal face for the left turn may be due to geometry, such as if the left turn lane is separated from the adjacent thru lanes by a short median or other buffer. Here's an example from Las Vegas: Craig Road at Rainbow Blvd (http://maps.google.com/maps?f=q&source=s_q&hl=en&geocode=&q=Craig+Road+and+Rainbow+Blvd,+Las+Vegas,+NV&sll=37.0625,-95.677068&sspn=45.197878,93.076172&ie=UTF8&hq=&hnear=W+Craig+Rd+%26+N+Rainbow+Blvd,+Las+Vegas,+Clark,+Nevada+89108&ll=36.240522,-115.241736&spn=0.001276,0.005681&t=h&z=18&layer=c&cbll=36.240522,-115.241736&panoid=nNSyDsK6hg1iobjCMOlLzw&cbp=11,274.08,,0,1.01) (Google Map/Street View).
Probably the more likely reason for the separate left turn doghouse has to do with a semi-recent push (last 10 years or so) by many agencies to install one signal head per lane on an approach. As far as I'm aware, this isn't a mandated standard anywhere, but is recommended for a number of reasons. In any event, this would be interpreted to include the left turn lanes. Having a separate face also gives agencies more options in dealing with the lefts. For example, there's intersections around Las Vegas that use a doghouse signal but, due to safety concerns, have protected-only lefts during peak hours. In this case, the circular indications are dark during the adjacent thru phase (and a louvered circular red or red arrow is used instead).
The "Left Turn Signal" sign, such as those pictured, were developed to please agencies that did not implement arrow signals right away. The sign was necessary to distinguish the circular indications in the left turn face from those in the adjacent thru faces, which were frequently different (and in my opinion was a greater safety hazard than Dallas Phasing). They were also used for where a left turn face had green and yellow arrows but used a circular red (a signal face arrangement I've never understood). Such signs are not needed where a full arrow display is used, as appears to be the case in the links provided.
Incidentally, the "Left Turn Signal" sign is no longer present in the MUTCD. The 2009 version did away with signal arrangements that would require the sign to be used, such as the circular red with other arrows. The reasoning behind this is that arrow signals have been around for over 30 years now, and having circular indications in a 3-section head for protected left turns is no longer necessary and can be confusing to motorists.
Quote from: roadfro on January 22, 2010, 05:22:18 PM
Probably the more likely reason for the separate left turn doghouse has to do with a semi-recent push (last 10 years or so) by many agencies to install one signal head per lane on an approach. As far as I'm aware, this isn't a mandated standard anywhere, but is recommended for a number of reasons. In any event, this would be interpreted to include the left turn lanes.
I believe this practice is frowned upon in the new MUTCD. They now recommend against protected/permissive, or permissive only, left turn lanes from having their own signal head. See http://mutcd.fhwa.dot.gov/services/ppt/mutcd09training/mutcd09part4.ppt, slide 25.
Quote from: roadfro on January 22, 2010, 05:22:18 PM
They were also used for where a left turn face had green and yellow arrows but used a circular red (a signal face arrangement I've never understood)... Incidentally, the "Left Turn Signal" sign is no longer present in the MUTCD. The 2009 version did away with signal arrangements that would require the sign to be used, such as the circular red with other arrows. The reasoning behind this is that arrow signals have been around for over 30 years now, and having circular indications in a 3-section head for protected left turns is no longer necessary and can be confusing to motorists.
It will be interesting to see what Indiana does about the red arrow (instead of circular red) rule for left turns. They have their own state MUTCD supplement where they specifically forbid red arrows until the legislature gives them a legal definition. Apparently, in the Indiana traffic law, they explicitly define what red, yellow, and green ball signals do, as well as yellow and green arrows, but they intentionally didn't define a red arrow signal as being legal in Indiana. The story goes that one of the older legislators feels that arrows indicate motion, not direction, so a red arrow was too confusing for use in Indiana. Folks there tend to resist change of any sort, so it's not surprising.
Quote from: realjd on January 22, 2010, 08:20:24 PM
Quote from: roadfro on January 22, 2010, 05:22:18 PM
Probably the more likely reason for the separate left turn doghouse has to do with a semi-recent push (last 10 years or so) by many agencies to install one signal head per lane on an approach. As far as I'm aware, this isn't a mandated standard anywhere, but is recommended for a number of reasons. In any event, this would be interpreted to include the left turn lanes.
I believe this practice is frowned upon in the new MUTCD. They now recommend against protected/permissive, or permissive only, left turn lanes from having their own signal head. See http://mutcd.fhwa.dot.gov/services/ppt/mutcd09training/mutcd09part4.ppt, slide 25.
The specific practice frowned upon is use of circular indications (particularly the green ball) in a separate signal face over the left turn lane. A separate permissive only or protected/permitted signal head is allowed for left turn lane, but it must be an all-arrow display (i.e. flashing yellow arrows).
Quote from: realjd on January 22, 2010, 08:20:24 PM
It will be interesting to see what Indiana does about the red arrow (instead of circular red) rule for left turns. They have their own state MUTCD supplement where they specifically forbid red arrows until the legislature gives them a legal definition. Apparently, in the Indiana traffic law, they explicitly define what red, yellow, and green ball signals do, as well as yellow and green arrows, but they intentionally didn't define a red arrow signal as being legal in Indiana. The story goes that one of the older legislators feels that arrows indicate motion, not direction, so a red arrow was too confusing for use in Indiana. Folks there tend to resist change of any sort, so it's not surprising.
Well something will have to give there. The states have two years to adopt the MUTCD or get a state manual/supplement together that's in "substantial compliance". So there will be time for Indiana to change the law.
A while back I was having a debate at another forum about whether you could turn right on a red arrow in Nevada if there is no sign prohibiting it. I found that Nevada law also doesn't explicitly define what a red arrow means, but does have definitions of other arrows. That hasn't stopped us from installing red arrows statewide.
Is roadfro an actual freak'in Civil Engineer or something?
I feel likea dumba$$ when it comes to roads when this guy talks....
^^^ :-D :-D :-D
I'm still unsure of why there are both arrows and balls on a signal for a single lane. I think "(color) ball/arrow" means protected, while "(color) ball only" means permitted.
Also, I still don't get how give opposing traffic a green, allowing turns, but restricting thru traffic helps increase capacity. Below is a picture from roadfro's video. I'm assuming the sides that aren't shown have a red signal.
(https://www.aaroads.com/forum/proxy.php?request=http%3A%2F%2Fmjr1990.webng.com%2FAARoads%2FPermitted%2520Left.png&hash=d900b6c168a9a77249fc7dcb044613c4bfc7d320)
Note that I would use a seperate signal head with left arrows (or balls with a "LEFT TURN SIGNAL" plaque) instead of a doghouse.
Quote from: Riverside Frwy on January 23, 2010, 03:55:14 PM
Is roadfro an actual freak'in Civil Engineer or something?
I feel likea dumba$$ when it comes to roads when this guy talks....
Not quite. I have a bachelor's degree in civil engineering, and have taken several civil engineering courses working towards a master's degree in that field with a traffic/transportation emphasis. I've also had a lifelong fascination with the operational aspects of traffic signs and signals. However, I am not currently employed as a civil engineer.
When I give a technical reply like these, I don't do it to make anyone feel less intelligent but rather to share what I know...especially as it relates to traffic engineering. I've often found that many people have an opinion when it comes to traffic, but don't necessarily realize the methods behind the engineers' madness. If I can help folks understand why something works the way it does, I feel it helps them be a little more informed and hopefully they don't diss all engineers in the future.
Quote from: Michael on January 23, 2010, 04:08:49 PM
I'm still unsure of why there are both arrows and balls on a signal for a single lane. I think "(color) ball/arrow" means protected, while "(color) ball only" means permitted.
A green arrow is the
only display that definitively indicates a protected turn. A "green ball+arrow" indication gives a protected left solely due to the presence of the green arrow.
I
think the reasoning behind the 5-section display has to do with what had been allowed for use as a permissive display. For many years, the national MUTCD had only defined one signal indication that would allow a permissive left turn: the circular green. Protected/permitted displays came later, and needed to find a way to indicate both protected and permitted operation in one display that also complied with the MUTCD.
Although some areas around the country had developed other methods of displaying permitted lefts (flashing red arrow, flashing red ball, flashing green arrow, flashing green ball, flashing yellow arrow), none were defined by the national MUTCD. Up until this new version, the only flashing signal operations defined by the national MUTCD were red flash mode (emergency all-way stop), red/yellow flash mode (nighttime operation), and beacons.
Quote from: Michael on January 23, 2010, 04:08:49 PM
Also, I still don't get how give opposing traffic a green, allowing turns, but restricting thru traffic helps increase capacity. Below is a picture from roadfro's video. I'm assuming the sides that aren't shown have a red signal.
(https://www.aaroads.com/forum/proxy.php?request=http%3A%2F%2Fmjr1990.webng.com%2FAARoads%2FPermitted%2520Left.png&hash=d900b6c168a9a77249fc7dcb044613c4bfc7d320)
In regards to capacity, this is specifically referring to the capacity of the northbound left turn, not the capacity of the entire northbound approach. More specifically, it helps more in decreasing delay than increasing capacity for that turn. The benefit comes from the extension of the permissive left turn interval. This can allow more time for permitted left turns to find a gap and complete the turn without needlessly making them wait for the next signal cycle. I'll try to explain it further.
At the point of the video shown above, the northbound left turn has already received its leading protected left turn for this cycle but the southbound lagging left turn is about to come on. The northbound thru vehicles have been stopped in anticipation for the southbound left turn, but the southbound thru vehicles still have a green. Say at this point, you have two vehicles in that northbound left turn lane. If this was a standard PPLT display, they would be seeing a circular red just like the adjacent thru traffic. Meanwhile, the opposing traffic is still going through. Conceivably, there would be gaps in the opposing through traffic at this point that the northbound left turn drivers could take advantage of, and continue to take advantage of until the cross street phase begins. Depending on the opposing traffic and length of the southbound protected left turn phase, both of the vehicles waiting in the northbound left turn lane might be able to complete their turn before the cross street phase begins. (In the animation, it's about 12 extra seconds to find a gap; in a real-world scenario with peak hour traffic, that time could be longer.) With the standard PPLT display, both of these vehicles would have to wait until the beginning of the next cycle (after cross traffic has had its turn).
Hopefully that made sense. I don't think I can make it clearer...
Quote from: Michael on January 23, 2010, 04:08:49 PM
Note that I would use a seperate signal head with left arrows (or balls with a "LEFT TURN SIGNAL" plaque) instead of a doghouse.
In a situation where both protected and permitted left turns are desired, a separate signal head with red/yellow/green arrows would not allow the permissive movement during the southbound thru phase. Similarly, a separate signal head with only red/yellow/green circular indications cannot be used for protected turns (regardless of whether it has a "Left Turn Signal" sign or not).
As of the 2009 MUTCD, the only methods for showing both protected and permitted left turns in a single signal face are a shared 5-section face (first example in the video) or a flashing yellow arrow face (third example in the video).
"Dallas Phasing" seems like a good idea if people will enter the gap on the green ball; however, I get behind people who won't turn into a gap on a "regular" permissive cycle -- they'll just sit and wait 'til the next cycle, treating the green ball like a red left turn arrow.
Be well,
Bryant
This is the first time I've ever seen the "yellow trap." When I saw the animation of it, my heart skipped a beat. That is probably the most dangerous traffic signal configuration I've seen. The light turns yellow, you wait for opposing traffic to stop so you can execute the left turn, and they don't stop. Am I missing something or is this just not a good idea?
As for Dallas phasing, there are three intersections in Salt Lake City with that configuration, all installed three or so years ago (the picture below is one of those at 1300 E. Sunnyside Ave if you want to Street View it). The first time I drove through it, there was a flashing yellow left-turn signal with a red through-lane signal. I was confused about what the traffic light was telling traffic exactly... Now I get what that signifies for left-turn traffic thanks to roadfro's excellent Powerpoint. The question is, does the general public?
(https://www.aaroads.com/forum/proxy.php?request=http%3A%2F%2Fupload.wikimedia.org%2Fwikipedia%2Fcommons%2F0%2F01%2F13that8th.jpg&hash=9b7c86ebadd939e7e8d851211ad9c02bc1c67163)
I should clarify that "Dallas Phasing" specifically refers to the unique signal phasing scheme using the 5-section PPLT display. 4-section flashing yellow arrow displays accomplish the same thing as Dallas Phasing display, but its use is not referred to as Dallas Phasing. A technicality, I know.
Most jurisdictions have not used lead/lag left turns with PPLT displays for the sole reason of not introducing a yellow trap situation. So yes, it was far from an ideal situation. Dallas Phasing was specifically developed for those agencies that needed to run lead/lag PPLT displays for signal timing progression purposes, in order to prevent the yellow trap.
The first flashing yellow arrows were developed in Reno, NV. The city engineer at the time (an acquaintance of my for a few years now) was instrumental in getting it implemented. From what he told me once, Reno installed flashing yellow arrows with little fanfare, and the public took to it relatively quickly. Ironically, there have been no FYA displays in Reno for at least 9 years now (regime change came, and the new city engineer had many of the installations replaced with protected-only signals).
This has been discussed in an older FYA thread, but I'll mention it again. An NCHRP study was the impetus behind getting FYA displays approved by the FHWA. That study looked at every known PPLT display that was in existence in the U.S. at the time. They also used simulations to test driver comprehension of the various displays. The FYA display was shown to be the most understood, even more so than the 5-section displays. Apparently, it's understood well enough that FHWA didn't even develop a standard sign for it in the MUTCD (I believe the interim approval stated a sign similar to the R10-12 could be used, but this was not retained).
Quote from: roadfro on January 24, 2010, 01:59:52 AM
Apparently, it's understood well enough that FHWA didn't even develop a standard sign for it in the MUTCD (I believe the interim approval stated a sign similar to the R10-12 could be used, but this was not retained).
The sign I've seen is "Left Turn Yield ON
<-- " (being a Yellow arrow on a black circle). I need to get a couple photos for my files.
Quote from: US71 on January 21, 2010, 01:54:12 PM
For the sake of clarification, here is a photo of the signal in question:
(https://www.aaroads.com/forum/proxy.php?request=http%3A%2F%2Ffarm5.static.flickr.com%2F4047%2F4292968965_412a54c2e5.jpg&hash=a4581835c8fd4ab1e5e0bb56ae9405c3d862e9c9)
A Left Turn is permitted, but not protected while oncoming WB traffic has steady Green. BUT thru traffic going EB still has Red.
This "Dallas Phasing" is being used in Fayetteville, AR at the intersection of 112 & 112-S? I can imagine accidents there as this would be a very unexpected sequence. Instead of the green ball, a flashing yellow arrow should be used. This is much more self-explanatory to the drivers, IMO.
Quote from: shoptb1 on January 24, 2010, 03:29:13 PM
This "Dallas Phasing" is being used in Fayetteville, AR at the intersection of 112 & 112-S? I can imagine accidents there as this would be a very unexpected sequence. Instead of the green ball, a flashing yellow arrow should be used. This is much more self-explanatory to the drivers, IMO.
Also at 6th St & Futrall (NB 540) for WB traffic. Those are the only 2 I've seen.
Fayetteville has NO Flashing Yellow Arrow signals at this time.
Accidents? Hell yes! See the white car in the distance? The Honda hit her, but kept going.
Quote from: US71 on January 24, 2010, 03:56:12 PM
Quote from: shoptb1 on January 24, 2010, 03:29:13 PM
This "Dallas Phasing" is being used in Fayetteville, AR at the intersection of 112 & 112-S? I can imagine accidents there as this would be a very unexpected sequence. Instead of the green ball, a flashing yellow arrow should be used. This is much more self-explanatory to the drivers, IMO.
Accidents? Hell yes! See the white car in the distance? The Honda hit her, but kept going.
I can believe that confusion about the phasing might lead to accidents. Just from what I can tell looking at the picture, if the Honda hit that white car it was probably more from driver stupidity than confusion about the signal display. Not knowing what the signal was doing at the time, it's hard to say.
In general, from my understanding, there has been increased instances of drivers mistaking a circular green for a protected turn. This has applied not only to 5-section PPLT displays, but also at standard 3-section displays with circular indications that are mounted over the left turn lane. This is why the 2009 MUTCD has taken the step of prohibiting a circular green indication in a signal face mounted over left turn lanes.
Quote from: roadfro on January 24, 2010, 04:57:52 PM
I can believe that confusion about the phasing might lead to accidents. Just from what I can tell looking at the picture, if the Honda hit that white car it was probably more from driver stupidity than confusion about the signal display. Not knowing what the signal was doing at the time, it's hard to say.
The problem here is that these signals (and every other signal in Arkansas) have always previously only allowed the solid green ball on a left-turn-lane mount WHEN the through lanes are also solid green balls. It's hard to re-train all of the drivers...especially when half of them are on auto-pilot and probably using a cell phone at the time anyway. At any rate, my point is that the most dangerous part of this all is the fact that it wasn't always this way. It almost needs a sign, like 'New Traffic Pattern'.
Quote from: shoptb1 on January 24, 2010, 06:01:50 PM
The problem here is that these signals (and every other signal in Arkansas) have always previously only allowed the solid green ball on a left-turn-lane mount WHEN the through lanes are also solid green balls. It's hard to re-train all of the drivers...especially when half of them are on auto-pilot and probably using a cell phone at the time anyway. At any rate, my point is that the most dangerous part of this all is the fact that it wasn't always this way. It almost needs a sign, like 'New Traffic Pattern'.
Drivers making a left turn shouldn't be paying attention to the thru traffic signals if there's a separate left turn signal face. The green ball in the left turn face is the only one that matters, regardless of whether the adjacent thru traffic had circular red or circular green. That should be inherent driving instinct that does not require driver retraining--although I realize this is a viewpoint derived in theory, not reality...
For those drivers on auto pilot or are otherwise distracted, a "New Traffic Pattern Ahead" sign won't make a bit of difference.
Quote from: roadfro on January 24, 2010, 08:09:23 PM
For those drivers on auto pilot or are otherwise distracted, a "New Traffic Pattern Ahead" sign won't make a bit of difference.
I cannot argue with you here. :banghead:
Quote from: US71 on January 24, 2010, 03:56:12 PM
Accidents? Hell yes! See the white car in the distance? The Honda hit her, but kept going.
Did you tell the person in the white car that they got hit by the car bearing Arkansas license plate 116 LNK?
Quote from: shoptb1 on January 24, 2010, 06:01:50 PM
It's hard to re-train all of the drivers...especially when half of them are on auto-pilot and probably using a cell phone at the time anyway.
Solution: "BOTTOMLESS PIT AHEAD" signs. The autopilot drivers fall into the pit and the ones who read signs avoid it!
Quote from: Scott5114 on January 24, 2010, 09:26:43 PM
Solution: "BOTTOMLESS PIT AHEAD" signs. The autopilot drivers fall into the pit and the ones who read signs avoid it!
We actually have those in Ohio...although they're unsigned. I believe the locals up here call them "pot holes" :)
^^ :-D
Yeah, got a lot of those here.
Be well,
Bryant
Quote from: shoptb1 on January 24, 2010, 09:29:46 PM
We actually have those in Ohio...although they're unsigned. I believe the locals up here call them "pot holes" :)
Iowa signs their potholes... at least on the dirt roads
(https://www.aaroads.com/forum/proxy.php?request=http%3A%2F%2Ffarm4.static.flickr.com%2F3242%2F2474629355_b45b3bc8ec.jpg&hash=27538162641ec28f769b7377e36e46d832120d34)
So does South Dakota
(https://www.aaroads.com/forum/proxy.php?request=http%3A%2F%2Ffarm3.static.flickr.com%2F2484%2F3980598340_1ab3f7497f.jpg&hash=7c30d5abef5b28d60746a71fddd7fd6ee80ca22b)
Quote from: US71 on January 25, 2010, 11:09:32 AM
Iowa signs their potholes... at least on the dirt roads
So does South Dakota
I am pretty sure that we would run out of signs here in Ohio if that was the case. :)
Quote from: US71 on January 25, 2010, 11:09:32 AM
Quote from: shoptb1 on January 24, 2010, 09:29:46 PM
We actually have those in Ohio...although they're unsigned. I believe the locals up here call them "pot holes" :)
Iowa signs their potholes... at least on the dirt roads
NY does something similar - we have regulatory-style signs (white BG, black legend) that say:
"Seasonal Limited Use Highway - No Maintenance NOV 1-APR 1"
Getting back on topic:
I'm still not sure what someone is supposed to do on a ball/arrow phase. If only I lived in Dallas...
Quote from: Michael on January 25, 2010, 03:13:33 PM
Getting back on topic:
I'm still not sure what someone is supposed to do on a ball/arrow phase. If only I lived in Dallas...
Well, traffic intending to turn in a direction of a green arrow may do so regardless of the circular indication, whether in a Dallas display or a shared display. If the circular display is red, you can still proceed with any turn indicated by a green arrow. Generally, if you don't see an arrow and your lane isn't controlled by a dedicated turn signal, you do whatever the circular indication indicates.
I've been doing a little research and it appears Dallas Phasing also appears in St Louis
http://www.stltoday.com/stltoday/news/columnists.nsf/alongfortheride/story/5F0930567EC485CE8625769E0011EDBD?OpenDocument
I wonder how many other towns do this (too many to count, I'd guess)?
Quote from: Michael on January 25, 2010, 03:13:33 PM
Getting back on topic:
I'm still not sure what someone is supposed to do on a ball/arrow phase. If only I lived in Dallas...
It's really quite simple: If you have a green arrow, you go. If you have a green ball, you yield first before you go. If both are on at the same time, the green arrow trumps the green ball. It doesn't matter what the adjacent signals are showing, just the left turn signal head.
Quote from: US71 on January 25, 2010, 06:30:41 PM
I've been doing a little research and it appears Dallas Phasing also appears in St Louis
http://www.stltoday.com/stltoday/news/columnists.nsf/alongfortheride/story/5F0930567EC485CE8625769E0011EDBD?OpenDocument
I wonder how many other towns do this (too many to count, I'd guess)?
It seemed to me that there're a lot of yellow traps in St. Louis based on that column, not necessarily Dallas phasing. The gist of this seems more to be Missourans' reluctance to enter an intersection on a permissive turn. I'm still scratching my head over what much of the commenters are saying. :hmmm:
As for other locations for Dallas phasing, no jurisdiction that I know of in Michigan has ever done it, and considering the state was (somewhat surprisingly) a fairly early adopter of the flashing-yellow arrow and the 2009 MUTCD's outright prohibition on Dallas phasing, I highly doubt I'll ever see it here.
Quote from: roadfro on January 25, 2010, 06:52:58 PM
Quote from: Michael on January 25, 2010, 03:13:33 PM
Getting back on topic:
I'm still not sure what someone is supposed to do on a ball/arrow phase. If only I lived in Dallas...
It's really quite simple: If you have a green arrow, you go. If you have a green ball, you yield first before you go. If both are on at the same time, the green arrow trumps the green ball. It doesn't matter what the adjacent signals are showing, just the left turn signal head.
I get that, but I'm talking about a doghouse dedicated to a left turn lane, shielded from view of thru traffic.
Quote from: rawmustard on January 26, 2010, 10:15:49 AM
As for other locations for Dallas phasing, no jurisdiction that I know of in Michigan has ever done it, and considering the state was (somewhat surprisingly) a fairly early adopter of the flashing-yellow arrow and the 2009 MUTCD's outright prohibition on Dallas phasing, I highly doubt I'll ever see it here.
If I recall correctly, Michigan was one of the states that had developed a different display for PPLT. I want to say it was a 3-section arrow display, maybe with flashing red. Dallas Phasing wouldn't have been considered then, because 5-section faces weren't used.
Quote from: Michael on January 26, 2010, 11:52:28 AM
Quote from: roadfro on January 25, 2010, 06:52:58 PM
Quote from: Michael on January 25, 2010, 03:13:33 PM
I'm still not sure what someone is supposed to do on a ball/arrow phase. If only I lived in Dallas...
It's really quite simple: If you have a green arrow, you go. If you have a green ball, you yield first before you go. If both are on at the same time, the green arrow trumps the green ball. It doesn't matter what the adjacent signals are showing, just the left turn signal head.
I get that, but I'm talking about a doghouse dedicated to a left turn lane, shielded from view of thru traffic.
So am I. The signal indications don't mean anything different just because they are in a separate face that only the left turn lane sees.
If it's any consolation, one of the primary reasons for switching to the FYA display is to eliminate confusion experienced by many drivers when encountering both arrow and circular indications simultaneously in a signal face--especially when a red ball and a green arrow are on at the same time.
Quote from: roadfro on January 26, 2010, 07:37:36 PM
If I recall correctly, Michigan was one of the states that had developed a different display for PPLT. I want to say it was a 3-section arrow display, maybe with flashing red. Dallas Phasing wouldn't have been considered then, because 5-section faces weren't used.
Yes, Michigan was big on the flashing red ball for PPLT display. From what I've heard or read, it was always meant to be a yield and not necessarily a full stop despite the legal definition of flashing red. Five-section heads didn't really start appearing in the state until the mid-to-late 1980s. I can still recall that the
Kalamazoo Gazette ran an article when the city of Portage introduced the doghouse to replace most of their intersections which had been using protected-only lead lefts (and a few years before that, those intersections were using flashing red lag lefts). I just marvel at how quickly Michigan decided to join the flashing yellow arrow trend, because they've been slow to catch on to other trends (e.g., the solid yellow arrow :-o).
UPDATE:
Fayetteville, AR has NO interest in upgrading to Flashing Yellow Arrows. They see no need.
Bentonville will be upgrading several signals along AR 102 to FYA's, but probably not until next year.
There's no requirement to upgrade existing signals to FYA. However, new signals are supposed to use FYA and signals are supposed to be upgraded to FYA is modified or reconstructed. Existing 5-section heads can also remain if they aren't separate heads and the circular indications always display the same as the through signals.
For many jurisdictions, this likely means that there will be no immediate changeover to FYA from 5-section PPLT heads (mainly because Dallas Phasing isn't that widespread). I imagine many agencies will put off changing over for a while, as many older signal controllers either cannot implement flashing yellow arrow phasing or require software reprogramming to do so. Furthermore, changing to FYA requires a capital expense for new signal heads and controller cabinet modifications, money that many public entities are likely holding on to unless absolutely necessary.
With that said, it's good to see more agencies considering switching to FYAs. I've been told Nevada DOT is considering implementation of FYAs statewide. It's an issue that they will have to work out with the various cities and counties, as those agencies are the ones that maintain traffic signals (even on state highways). I believe Las Vegas and Clark County have been somewhat resistant to changing to FYAs, preferring a modified use of the 5-section doghouse in switching between protected and permitted modes. The only installations of FYA I'm aware of in Nevada are two signals in Carson City (on Fairview Drive/Temp US 395-50).
http://ow.ly/1nVUF
Although Salt Lake City has been experimenting with these for a few years, UDOT is now officially implementing signals with Dallas phasing.
I posted in the SW section that Nevada DOT is looking at statewide implementation of FYA. No mention of the phase-in timeline or any immediate retrofit/upgrade plans.
I've seen several FYA left turn setups in the Charlotte, NC area while I've been down here (for only about a week).
Man, I'm glad I read this. I would have thought that the light was malfunctioning. I wouldn't have thought that I had a protected left turn though.
Quote from: burgess87 on March 18, 2010, 11:06:15 PM
I've seen several FYA left turn setups in the Charlotte, NC area while I've been down here (for only about a week).
Last time I was stick in that dump of a town Fayetteville, NC, they had FYA's as well.
Quote from: AZDude on March 22, 2010, 02:24:45 AM
Man, I'm glad I read this. I would have thought that the light was malfunctioning. I wouldn't have thought that I had a protected left turn though.
I think you mean permitted left turn, if referring to a green ball or flashing yellow arrow.
Quote from: roadfro on March 22, 2010, 03:41:03 PM
Quote from: AZDude on March 22, 2010, 02:24:45 AM
Man, I'm glad I read this. I would have thought that the light was malfunctioning. I wouldn't have thought that I had a protected left turn though.
I think you mean permitted left turn, if referring to a green ball or flashing yellow arrow.
In a way, yes because I would have not thought of it as a green arrow.
As stated by US 71, a driver thought they had a protected left turn (because they saw the green ball, thinking it was the same as a green arrow) and crashed into an oncomming car.
If I were at that intersection at that time, I would have stayed there and waited as if it were a regular red light because I would have thought the signal was malfunctioning.
Quote from: roadfro on January 22, 2010, 12:33:16 AM
This took me a little while to finish up, but I hope you all will find it helpful. I've created a short video that explains in a graphic format the differences between the various forms of protected/permitted left turn controls, including Dallas Phasing.
By no means am I a whiz with video capture and online videos, so I hope it works okay. Here it is: http://www.youtube.com/watch?v=KPKjcPI5Sko
I did enjoy this video because it explained everything perfectly, as I've never heard of this type of setup before. Great job, roadfro! It's a good thing Dallas Phasing is not used down here.
Quote from: roadfro on January 22, 2010, 12:33:16 AM
This took me a little while to finish up, but I hope you all will find it helpful. I've created a short video that explains in a graphic format the differences between the various forms of protected/permitted left turn controls, including Dallas Phasing.
By no means am I a whiz with video capture and online videos, so I hope it works okay. Here it is: http://www.youtube.com/watch?v=KPKjcPI5Sko
This video is very good as it helps explain the differences. In my opinion, the Flashing Yellow Arrow (FYA) is the best visual descriptor to the driver to help them from confusing the green ball from the green arrow intentions.
There is a pseudo-variation of this in Fort Lauderdale, but it's only used at U-turn signals (dotted along US 1 mostly). The red phase will flash, and you can either come to a complete stop to wait for traffic to clear. If you're there too long, it will change to a solid green arrow to make your U-turn (opposing traffic will be stopped of course), then a solid yellow arrow, and back to flashing red.
I noticed a couple of FYA assemblies in Marysville, WA for the first time yesterday, not sure how recent a development that is.
The "variation" (if you can call it that) that I've seen most often in this part of the country doesn't use any special phasing. Rather, at several intersections where the intersecting street is only one side of the road (i.e. T-intersection), they just tack on a sign over the left turn lane that says "Stop on (red ball), then left turn permitted". Still requires you to stop instead of yield, but it does the job.