Traffic signal

[jakeroot]

I've found an example of Dallas Phasing in Washington State. Keene Road @ Englewood/Westcliffe, Richland:

https://goo.gl/kDM8jE

The left turn doghouses (aligned in the Colorado style -- also unusual) have louvres placed over the signal faces. Judging by street view imagery, the signals seem to run independently of the through traffic signals. Since I haven't been to the Tri-Cities for several years, I cannot confirm my suspicions. But the capture below, plus the signal louvres seem to suggest Dallas phasing.

Kind of makes me wonder...how many signals with Dallas Phasing still exist? I think even Texas has gotten rid of most of theirs. I never realised an example of it existed up here.

Isn't the doghouse with the red indication (while the other heads are green) an MUTCD violation?

Normally, I think it would be, yes. But it's a hallmark trait of Dallas phasing: the doghouse above the left turn lane runs completely independent of the through signals, so you can get these strange red/green combos. The louvres try to keep drivers from looking at the wrong signals.

The catch is, I can't quite figure out why, in the photo I posted, the left turn doghouse had the red orb lit up at all. If it was a leading left, even with Dallas phasing, the green orb should have been lit. The signal must have went red briefly, following the protected phase. This is evidenced by the very next Street View frame, showing a green orb: https://goo.gl/QcuAA5

P.S. This is the first time I've ever heard of "Dallas phasing," so excuse my ignorance on the subject.

Not to worry. It's a very unusual setup...

So if the doghouse is intended to be viewed only by traffic using the left turn lane, why even have a doghouse at all, as opposed to, say, a simple three section head?

The idea with Dallas phasing was to allow protected/permissive left turns with lead/lag phasing, by using louvres to prevent traffic in parallel lanes from seeing each other's signals (making it so through traffic could see one signal, but left turners see another). Because both signals used orbs, louvres were necessary to prevent confusion, and most importantly, prevent yellow trap (you'd need to ensure that left turning traffic, whose left turn was leading, didn't turn into traffic when the oncoming left turn's lagging protected movement flipped the through signal's light to red).

Now, with the advent of the FYA, and its all-arrow displays, Dallas phasing is no longer necessary. There's literally nothing to hide anymore.

Our very own roadfro made a video some time ago, detailing the operation of these signals:

https://youtu.be/KPKjcPI5Sko

[US 89]

So if the doghouse is intended to be viewed only by traffic using the left turn lane, why even have a doghouse at all, as opposed to, say, a simple three section head?

P.S. This is the first time I've ever heard of "Dallas phasing," so excuse my ignorance on the subject.

Dallas phasing is basically using a protected/permissive signal as a left turn signal. So in that photo above, the doghouse is intended to be used only by left turn traffic. The reason a 5-section head has to be used instead of a 3-section is that you want both protected and permissive indications. If the green light and arrow both come on, you get a protected left. If just the green light comes on, you get a permissive left.

They aren't installed anymore because FYA does the same thing in a much clearer, easier-to-understand way.

[SignBridge]

Guys, there is some confusion here with terminology. The left-turn signal shown in the photo above while it's similar to a doghouse, and works the same, is commonly called a side-by-side

Contrary to what someone said above, they are still permitted by the current MUTCD and are still being installed. They are called "shared signals" because they control both the left-turn and thru movements, and are required to always show the same circular-light color as the adjacent thru signals. The Manual suggests they be mounted between the left-thru lane and the left-turn lane to emphasize their "shared" function.

These signals are not Dallas Phasing. What Dallas Phasing actually does is it shows a green-ball over the left-turn lane while the heads over the thru-lanes are red. It allowed permissive left turns while thru traffic is stopped. And this is what the MUTCD no longer allows and now requires a flashing-yellow in its place.  Do a Google search for Dallas Phasing and you'll find some illustrations that explain it better.

[MNHighwayMan]

Guys, there is some confusion here with terminology. The left-turn signal shown in the photo above while it's similar to a doghouse, and works the same, is commonly called a side-by-side

Contrary to what someone said above, they are still permitted by the current MUTCD and are still being installed. They are called "shared signals" because they control both the left-turn and thru movements, and are required to always show the same circular-light color as the adjacent thru signals. The Manual suggests they be mounted between the left-thru lane and the left-turn lane to emphasize their "shared" function.

These signals are not Dallas Phasing. What Dallas Phasing actually does is it shows a green-ball over the left-turn lane while the heads over the thru-lanes are red. It allowed permissive left turns while thru traffic is stopped. And this is what the MUTCD no longer allows and now requires a flashing-yellow in its place.  Do a Google search for Dallas Phasing and you'll find some illustrations that explain it better.

But the signal in jakeroot's picture is displaying a different indication and is centered over the left turn lane?

[SignBridge]

The rules in the 2009 Manual apply to new and rebuilt signals only. The signal in the photo is apparently an older one, similar to thousands still in use nationwide. The Manual allows them to continue in-service until they are rebuilt or replaced.

[jakeroot]

What I was trying to say above was that Dallas Phasing was no longer allowed (or was obsolete), not that shared signal faces (be them doghouses or side-by-side signals) were no longer allowed. They still have plenty of uses, chiefly when there is no dedicated left turn lane.

The signal in the photo above, as far as I can tell, is in fact Dallas Phasing, that for no apparent reason, utilises a side-by-side 5-section display (extremely rare in Washington, hence the reason that I brought it up at all). The red orb and the green orb would not be lit at the same time if it weren't Dallas Phasing. That's the only setup that would allow such a thing. Minus a shared signal face that had its faces replaced by arrows (seen in Colorado quite a lot).

[US 89]

The way I understand it, because the left turn signal is showing a ball indication that is different from the through lanes, it is Dallas phasing. The equivalent FYA display to what is shown in the picture would be a red left arrow and two green balls for through traffic.

Having two different ball indications facing the same direction at the same time is what is banned in new signals by the current MUTCD. Doghouses installed today must have the ball indicators match the through lane indicators, and be placed between the left turn lane and the leftmost through lane.

In addition, if you move around that GSV, you'll see that the balls in the left turn signal head are louvered and so are not visible to the through lanes. Another clear indicator of Dallas phasing.

[roadfro]

Our very own roadfro made a video some time ago, detailing the operation of these signals:

Thanks for the shoutout

I made that almost 8 years ago. To date, it's the only video I've ever posted on YouTube. (The complexity of the PowerPoint animations took me quite a while.)

The signal in the photo above, as far as I can tell, is in fact Dallas Phasing, that for no apparent reason, utilises a side-by-side 5-section display (extremely rare in Washington, hence the reason that I brought it up at all). The red orb and the green orb would not be lit at the same time if it weren't Dallas Phasing. That's the only setup that would allow such a thing. Minus a shared signal face that had its faces replaced by arrows (seen in Colorado quite a lot).

It might not be Dallas Phasing... True that Dallas Phasing allows the turn lane and thru lanes to have different circular indications at the same time. However, seeing thru lanes green and a turn lane red doesn't quite jive with Dallas Phasing, since it should be allowing the left turn lane to have a circular green at the same time as the adjacent or opposing thru.


Another explanation for what is seen in the photo is time-of-day protected vs. protected/permitted phasing. This is something that was done for a while at select intersections in the Las Vegas area. In these cases, a doghouse with Dallas Phasing-style louvers was used over all circular indications of the 5-section head. During busy peak periods, where permitted left turns were unlikely to have a sufficient gap in the opposing traffic, the signal operated in protected-only mode and the circular red was displayed during adjacent and opposing thru greens. However, off-peak, the circular green was able to be displayed when appropriate. (Interestingly, at some of these setups, a red arrow was used at the top instead of using a louvered circular red. I didn't care for that variant at all, as a circular green/yellow looks odd being terminated by a red arrow.)

As Nevada embraced the FYA display quickly after the 2009 MUTCD was implemented, NDOT made funding available to local agencies so they could start replacing 5-section PPLT displays with 4-section FYAs. As I recall, most of the intersections in the Las Vegas area running Dallas Phasing and/or this time-of-day protected with 5-section heads were among the first to have the signal heads changed.

[jakeroot]

It might not be Dallas Phasing... True that Dallas Phasing allows the turn lane and thru lanes to have different circular indications at the same time. However, seeing thru lanes green and a turn lane red doesn't quite jive with Dallas Phasing, since it should be allowing the left turn lane to have a circular green at the same time as the adjacent or opposing thru.

Another explanation for what is seen in the photo is time-of-day protected vs. protected/permitted phasing. This is something that was done for a while at select intersections in the Las Vegas area. In these cases, a doghouse with Dallas Phasing-style louvers was used over all circular indications of the 5-section head. During busy peak periods, where permitted left turns were unlikely to have a sufficient gap in the opposing traffic, the signal operated in protected-only mode and the circular red was displayed during adjacent and opposing thru greens. However, off-peak, the circular green was able to be displayed when appropriate. (Interestingly, at some of these setups, a red arrow was used at the top instead of using a louvered circular red. I didn't care for that variant at all, as a circular green/yellow looks odd being terminated by a red arrow.)

I was curious about that when I first stumbled upon the signal. It should be green, not red, if the left turn was leading. But I did post two Street View links, in addition to the image above, which you can see here:

Frame 1: https://goo.gl/kDM8jE
Frame 2: http://goo.gl/QcuAA5

In frame 1, the signal is red. But literally seconds later (judging by the oncoming cars having moved off), the signal changes to green. My assumption, after having then considered this, was that the signal phasing was green arrow > yellow arrow > red ball > green ball > yellow ball > red ball. Basically, the same behavior as most FYAs, just without the all arrow displays. Basically, I'm still pretty sure it's Dallas Phasing, just a slight modification of the traditional setup.

I mentioned this oddity upthread:

The catch is, I can't quite figure out why, in the photo I posted, the left turn doghouse had the red orb lit up at all. If it was a leading left, even with Dallas phasing, the green orb should have been lit. The signal must have went red briefly, following the protected phase. This is evidenced by the very next Street View frame, showing a green orb: https://goo.gl/QcuAA5

[roadfro]

^ I must have overlooked your street view frame observation the first time. That explanation certainly works...and it could be that all the circular indications were tied to the opposing thru signals (which isn't 100% typical with Dallas Phasing)

[jakeroot]

I have never seen an overhead traffic signal in British Columbia without a backplate...lo and behold, the intersection of Fort, Oak Bay, and Pandora in suburban Victoria: https://goo.gl/iSo3Gw

Hardly interesting to most of you, but very unusual for BC. There are more in Victoria, glancing around on Street View. Never realised such a setup existed in BC; I haven't been out on Vancouver Island for 10+ years. Only noticed this signal due to a CBC News story.

[jakeroot]

This one pedestrian head in Puyallup, WA kept catching my eye, but I only noticed why yesteday. For some reason, whenever a "4" is displayed, there's an extra line on the bottom of the number (like a lowercase "y"), and whenever a "0" is displayed, there's an extra line across the middle (making it look like an "8").

https://goo.gl/De4d7L

https://youtu.be/-qyQdVz6les

[jakeroot]

Does anyone know if this is allowed?

In Renton, WA, at the off-ramp to Talbot Road from southbound 405, one of the two thru-signals is posted near-side. From the stop line, only the far-side signal is visible (the near-side signal is mounted too far back). I'm pretty sure two far-side signals (both in the stop-line cone of vision) are required before any secondary signals can be considered. Out of image, there is also a near-side left turn signal. I appreciate WSDOT going the extra mile by using near-side signals, but I'd also appreciate an extra far-side signal if possible.

https://goo.gl/JSEgHG

[roadfro]

Does anyone know if this is allowed?

In Renton, WA, at the off-ramp to Talbot Road from southbound 405, one of the two thru-signals is posted near-side. From the stop line, only the far-side signal is visible (the near-side signal is mounted too far back). I'm pretty sure two far-side signals (both in the stop-line cone of vision) are required before any secondary signals can be considered. Out of image, there is also a near-side left turn signal. I appreciate WSDOT going the extra mile by using near-side signals, but I'd also appreciate an extra far-side signal if possible.

https://goo.gl/JSEgHG

Depends on when the signal was installed. By 2003 MUTCD standards, I'm pretty sure this is acceptable, since you have a one-lane through movement and one primary signal located in the cone of vision. The 2009 MUTCD introduced a standard that dictates that two primary signals are required for the through movement in the cone of vision, even if the through movement is not the major movement on the approach.

[Ian]

Does anyone know if this is allowed?

In Renton, WA, at the off-ramp to Talbot Road from southbound 405, one of the two thru-signals is posted near-side. From the stop line, only the far-side signal is visible (the near-side signal is mounted too far back). I'm pretty sure two far-side signals (both in the stop-line cone of vision) are required before any secondary signals can be considered. Out of image, there is also a near-side left turn signal. I appreciate WSDOT going the extra mile by using near-side signals, but I'd also appreciate an extra far-side signal if possible.

https://goo.gl/JSEgHG

No idea on if it's allowed, but New Jersey has been known to put only one signal on both the far and near sides of an intersection.

https://goo.gl/maps/K7c2Jgia2bv

[jeffandnicole]

Does anyone know if this is allowed?

In Renton, WA, at the off-ramp to Talbot Road from southbound 405, one of the two thru-signals is posted near-side. From the stop line, only the far-side signal is visible (the near-side signal is mounted too far back). I'm pretty sure two far-side signals (both in the stop-line cone of vision) are required before any secondary signals can be considered. Out of image, there is also a near-side left turn signal. I appreciate WSDOT going the extra mile by using near-side signals, but I'd also appreciate an extra far-side signal if possible.

https://goo.gl/JSEgHG

No idea on if it's allowed, but New Jersey has been known to put only one signal on both the far and near sides of an intersection.

https://goo.gl/maps/K7c2Jgia2bv

That's generally an older layout.   Today, they are pretty good adhering to the one signal per lane concept, as shown on these newer signals on NJ 38.  https://goo.gl/maps/u61Z84jmNR82  They also continue to post one near-side traffic signal. 

[jakeroot]

Does anyone know if this is allowed?

In Renton, WA, at the off-ramp to Talbot Road from southbound 405, one of the two thru-signals is posted near-side. From the stop line, only the far-side signal is visible (the near-side signal is mounted too far back). I'm pretty sure two far-side signals (both in the stop-line cone of vision) are required before any secondary signals can be considered. Out of image, there is also a near-side left turn signal. I appreciate WSDOT going the extra mile by using near-side signals, but I'd also appreciate an extra far-side signal if possible.

https://goo.gl/JSEgHG

Depends on when the signal was installed. By 2003 MUTCD standards, I'm pretty sure this is acceptable, since you have a one-lane through movement and one primary signal located in the cone of vision. The 2009 MUTCD introduced a standard that dictates that two primary signals are required for the through movement in the cone of vision, even if the through movement is not the major movement on the approach.

The signal was installed in 2010. So, it sounds like they might not have gotten the memo in time.

[SignBridge]

Roadfro, you'd best check your 2009 Manual again. On page-463, Sec. 4D-13.01 repeats what previous Manuals said: "At least one and preferably both of the minimum of two primary signals required for the through movement" shall be located within the cone-of-vision visible from the stop-line.

So that 2010 installation in Renton, Wa. is still permitted by the MUTCD. But again, as in the past Manuals, the FHWA strongly encourages both required heads to be in the "cone". But that installation strictly speaking, is in-compliance. And I might add, it looks well-designed to me, given the geometry of that particular intersection, though a second green-ball on the far-side would be good too. 

[roadfro]

Does anyone know if this is allowed?

In Renton, WA, at the off-ramp to Talbot Road from southbound 405, one of the two thru-signals is posted near-side. From the stop line, only the far-side signal is visible (the near-side signal is mounted too far back). I'm pretty sure two far-side signals (both in the stop-line cone of vision) are required before any secondary signals can be considered. Out of image, there is also a near-side left turn signal. I appreciate WSDOT going the extra mile by using near-side signals, but I'd also appreciate an extra far-side signal if possible.

https://goo.gl/JSEgHG

Depends on when the signal was installed. By 2003 MUTCD standards, I'm pretty sure this is acceptable, since you have a one-lane through movement and one primary signal located in the cone of vision. The 2009 MUTCD introduced a standard that dictates that two primary signals are required for the through movement in the cone of vision, even if the through movement is not the major movement on the approach.

The signal was installed in 2010. So, it sounds like they might not have gotten the memo in time.

States are given two years after a new MUTCD is introduced to either adopt it verbatim, adopt verbatim with a state supplement, or create their own state MUTCD that is in substantial compliance with the national one. For the 2009 MUTCD, which was approved 1/15/2010, states had until 1/15/2012 to adopt. So it is entirely possible that this signal was installed in the interim and Washington (which appears to be a "adopt with state supplement" state, according to the MUTCD website) had not yet incorporated the new standard at the time of design or construction.

Roadfro, you'd best check your 2009 Manual again. On page-463, Sec. 4D-13.01 repeats what previous Manuals said: "At least one and preferably both of the minimum of two primary signals required for the through movement" shall be located within the cone-of-vision visible from the stop-line.

So that 2010 installation in Renton, Wa. is still permitted by the MUTCD. But again, as in the past Manuals, the FHWA strongly encourages both required heads to be in the "cone". But that installation strictly speaking, is in-compliance. And I might add, it looks well-designed to me, given the geometry of that particular intersection, though a second green-ball on the far-side would be good too. 

Ok, I was mistaken about both primary signal faces being in the cone of vision at the stop line. But compliance still depends on which version of MUTCD this was designed under. With 2009 MUTCD, two primary signal faces are still required for this movement. Since the second signal head is not 40-180 feet beyond the stop line, as required by Sec 4D.14 p01 and illustrated in Fig 4D-4, it cannot be considered a primary signal face. Therefore, the intersection still doesn't meet 2009 MUTCD standards for signal head placement.

I don't disagree with a supplemental signal head here though, given the curve on the off ramp (I'd have probably put in a near-side supplemental for the left turn also). But a second primary face would have been good to have even under 2003 standards.

[jakeroot]

I don't disagree with a supplemental signal head here though, given the curve on the off ramp (I'd have probably put in a near-side supplemental for the left turn also). But a second primary face would have been good to have even under 2003 standards.

You might be alluding to this because I already pointed it out, but WSDOT, in what I can only describe as totally out of character, did actually use a supplementary near-side left turn signal (check out the street view in the original post). If it were warranted anywhere, it would be this curve. Though, this region of the DOT is known for going off-script. The oncoming right turn has a supplementary right turn signal, and the left turn onto northbound I-405 on the other side of the freeway has a supplementary left turn signal. They almost had a perfect setup here. I intend to email WSDOT to ask about installing another far-side signal, just so I can complete the perfection.

[SignBridge]

Roadfro, I believe you may still be mistaken about the Manual's requirements. The section you cited (4D.14.01.A) also contains that same wording "at least one and preferably both" when specifying the range of 40 to 180 ft. from the stop line for the two primary signals.

I believe the writers of the Manual might have specifically worded it that way to allow for some flexibility for oddly angled intersections like the one in the Renton photo. It's all good.

Admittedly, the MUTCD is very complicated and we have to read it very carefully. I've made mistakes too and had to reread a section several times before I understood it. Especially the sections that outlawed "Dallas Phasing". They should give us college credits for this! LOL

[MNHighwayMan]

Admittedly, the MUTCD is very complicated and we have to read it very carefully. I've made mistakes too and had to reread a section several times before I understood it. Especially the sections that outlawed "Dallas Phasing". They should give us college credits for this! LOL

A college class on the ins-and-outs of the MUTCD would be amazing.

[jakeroot]

Admittedly, the MUTCD is very complicated and we have to read it very carefully. I've made mistakes too and had to reread a section several times before I understood it. Especially the sections that outlawed "Dallas Phasing". They should give us college credits for this! LOL

A college class on the ins-and-outs of the MUTCD would be amazing.

I'm sure civil engineering courses bring up the MUTCD from time to time.

[RestrictOnTheHanger]

I'm assuming that this relatively recent NYSDOT installation isnt MUTCD compliant on this approach

NY110 at Milbar Blvd

https://goo.gl/maps/BpxHfvDVEsL2

[jakeroot]

I'm assuming that this relatively recent NYSDOT installation isnt MUTCD compliant on this approach

NY110 at Milbar Blvd

https://goo.gl/maps/BpxHfvDVEsL2

Yikes. No, that's definitely not compliant. Looks like they modified the setup recently by removing the split-phasing, but forgot to account for the now-missing additional through head.