Traffic signal

[jakeroot]

Speaking of California: something that seems ridiculously rare in California but is otherwise pretty common elsewhere:

Double left turn with two overhead left turn signals (Burlingame).

Many would say, "why Jake, that's completely normal!" Not in California; the state pretty much universally uses '# of lanes minus one' for determining overhead signals. Hell, they have triple left turns with only one overhead signal, such as southbound Galleria at Roseville Parkway (in Roseville).

Now, to be clear, I've seen California use two overhead left turn signals for two lanes, but it seems largely reserved for situations where the double left is the primary movement, or when the double left turn is segregated away from the mainlines. Neither are the case at the Burlingame intersection.

[fwydriver405]

So how common are doghouse signals post-mounted (or even mounted in the median)? Usually, if post mounted signals are posted, a bimodal 4-section or vertical 5-section signal stack is used instead...

Median-mounted doghouse:
Centre St, Malden MA

Post-mounted doghouse:
Centre St and Commercial St, Malden MA
Mill Road and Hastings Road, Spokane WA (Dallas Phasing as well?)
Nevada Street and Francis Ave, Spokane WA

[Amtrakprod]

So how common are doghouse signals post-mounted (or even mounted in the median)? Usually, if post mounted signals are posted, a bimodal 4-section or vertical 5-section signal stack is used instead...

Median-mounted doghouse:
Centre St, Malden MA

Post-mounted doghouse:
Centre St and Commercial St, Malden MA
Mill Road and Hastings Road, Spokane WA (Dallas Phasing as well?)
Nevada Street and Francis Ave, Spokane WA

MA loves doghouses on the bottom, I could count 20+ locations with them. Spokane is a fan of them too. Also that's not Dallas phasing, just an eagle intersection.

[jakeroot]

So how common are doghouse signals post-mounted (or even mounted in the median)? Usually, if post mounted signals are posted, a bimodal 4-section or vertical 5-section signal stack is used instead...

Median-mounted doghouse:
Centre St, Malden MA

Post-mounted doghouse:
Centre St and Commercial St, Malden MA
Mill Road and Hastings Road, Spokane WA (Dallas Phasing as well?)
Nevada Street and Francis Ave, Spokane WA

MA loves doghouses on the bottom, I could count 20+ locations with them. Spokane is a fan of them too. Also that's not Dallas phasing, just an eagle intersection.

I would also call them a seagull. I think the green up arrows make it not Dallas phasing.

Spokane is the place that comes to mind when I think of post-mounted doghouses, though they do utilise 4-section protected/permissive left turns for lagging lefts (example here).

Spokane has installed a substantial number of flashing yellow arrows over the last few years, so I think the era of the post-mounted doghouse is coming to end in this part of the world.

[roadfro]

Mill Road and Hastings Road, Spokane WA (Dallas Phasing as well?)

Also that's not Dallas phasing, just an eagle intersection.

I would also call them a seagull. I think the green up arrows make it not Dallas phasing.

Dallas Phasing specifically refers to the practice of using 5-section displays with the circular yellow and green indications being visibility-limited, to allow the circular displays of the left turn face to operate independently from the adjacent through signals–specifically to allow permissive left turns to proceed on circular while adjacent through traffic display red, to allow implementation of lead-lag left turn phasing in efforts to achieve better signal coordination along an arterial.

"Seagull" intersection is such a weird phrase for this setup–not sure why there's such a prevalence for trying to name certain traffic control treatments after birds... In Nevada, this is referred to as a "High-T" intersection (whether signalized or not).

[jakeroot]

Mill Road and Hastings Road, Spokane WA (Dallas Phasing as well?)

Also that's not Dallas phasing, just an eagle intersection.

I would also call them a seagull. I think the green up arrows make it not Dallas phasing.

Dallas Phasing specifically refers to the practice of using 5-section displays with the circular yellow and green indications being visibility-limited, to allow the circular displays of the left turn face to operate independently from the adjacent through signals–specifically to allow permissive left turns to proceed on circular while adjacent through traffic display red, to allow implementation of lead-lag left turn phasing in efforts to achieve better signal coordination along an arterial.

"Seagull" intersection is such a weird phrase for this setup–not sure why there's such a prevalence for trying to name certain traffic control treatments after birds... In Nevada, this is referred to as a "High-T" intersection (whether signalized or not).

I've always seen "Dallas Phasing" used to refer to intersections where the left turn and through lanes have separate circular indications. This wouldn't be the case at this intersection because the through lanes use all-arrow indications. Japan does something similar: when they don't want to allow permissive turns, they keep the light red, but activate green arrows in all directions where they allow traffic to move.

[Amtrakprod]

Here's an example of Dallas Phasing I found in Austin TX:
Dallas Phasing by Petru Sofio, on Flickr

[mrsman]

Mill Road and Hastings Road, Spokane WA (Dallas Phasing as well?)

Also that's not Dallas phasing, just an eagle intersection.

While I don't often advocate changing doghouses into FYA signals, given what could be a somewhat confusing situation, I believe this would be a good candidate for the replacement.

Many of these intersections have a cyclops green arrow for straight thru traffic.  It's interesting to see RYG signal heads.  The reason for this is that there is still a pedestrian crossing, so if a ped wants to cross, these signals will turn red.  But no need for them to turn red just for cross traffic, which will turn left into the other lane.


I would also call them a seagull. I think the green up arrows make it not Dallas phasing.

Dallas Phasing specifically refers to the practice of using 5-section displays with the circular yellow and green indications being visibility-limited, to allow the circular displays of the left turn face to operate independently from the adjacent through signals–specifically to allow permissive left turns to proceed on circular while adjacent through traffic display red, to allow implementation of lead-lag left turn phasing in efforts to achieve better signal coordination along an arterial.

"Seagull" intersection is such a weird phrase for this setup–not sure why there's such a prevalence for trying to name certain traffic control treatments after birds... In Nevada, this is referred to as a "High-T" intersection (whether signalized or not).

I've always seen "Dallas Phasing" used to refer to intersections where the left turn and through lanes have separate circular indications. This wouldn't be the case at this intersection because the through lanes use all-arrow indications. Japan does something similar: when they don't want to allow permissive turns, they keep the light red, but activate green arrows in all directions where they allow traffic to move.

[jakeroot]

While I don't often advocate changing doghouses into FYA signals, given what could be a somewhat confusing situation, I believe this would be a good candidate for the replacement.

Many of these intersections have a cyclops green arrow for straight thru traffic.  It's interesting to see RYG signal heads.  The reason for this is that there is still a pedestrian crossing, so if a ped wants to cross, these signals will turn red.  But no need for them to turn red just for cross traffic, which will turn left into the other lane.

Based on what I know about Spokane, it probably will be replaced by an FYA signal in the future. They've become a lot more common.

One of the common complaints of the Seagull intersection (the term I prefer, just because visually it looks like a seagull's wings to me) is that it's not pedestrian friendly. Regular intersections aren't that great anyway, when considering crossing distances, signal timings, etc, but they go from "fine" to "not that great" the second you start adding in continuous flow movements. There are some acceptable situations of this, such as slip lanes where the angle is such that the crossing is more visible relative to older slip lane designs, but a continuous flow across the top of a T-intersection can become problematic since, more often than not, the continuous movement does not feature RYG signals to allow for pedestrian crossings. This is understandable in quiet areas with few pedestrians, but these intersections really ought to include RYG signals for the through movement to accommodate those pedestrians, even in quiet areas. If we don't modify the intersection to suit the pedestrian, the pedestrian will simply utilize the intersection in a way that meets their needs, irrespective of the apparent design. Adding in a crosswalk with RYG signals seems like a minor change to me; I don't understand why they aren't more common.


Slightly off-topic:

This talk of continuous flow movements reminds me of an interchange I designed (for myself, primarily) a while back. In the bottom right corner of the image, you can see a continuous flow movement that I've designed that would incorporate a pedestrian crossing. There seems to be two schools of thought on this: either put the crossing so that right-turning traffic must yield, or put it to the left so that left-turning traffic must yield. The vast majority of these intersections place it on the right, allowing left turns to proceed without yielding, but this might not be optimal if the heaviest movement is the left turn from the top of the "T" towards the stem, as it would be in this situation. This would permit left turns onto the on-ramp, and right turns from the off-ramp, to proceed at the same time, fully protected (although in my case, there is no right turn from the off-ramp, as that movement is accommodated by other ramps). This might not be ideal if the left turn from the off-ramp were heavy, but would be great if the primary movement was that left turn onto the on-ramp. The through traffic (along the top of the "T") would need to stop, with left turns having a green arrow, which is fairly unusual for these seagull intersections, but it's an operational advantage over a crosswalk that is on the right side of the "T". Alternatively, it could still be operated where the left turn from the off-ramp has to yield.

As well, the crossing had been designed so that the continuous movement (along the top of the "T") actually yielded to pedestrians using a zebra crossing and pedestrian crossing signs, rather than a signal. My thinking being that the movement was no different than a right-turn slip lane, except with much better visibility, so why not design it so that cars simply yield to pedestrians? I did scrap this plan, because I couldn't make the seagull island large enough to accommodate pedestrians waiting for a "WALK" signal due to limited ROW, and that the added lane needed to join with the other lane as soon as possible due to impending turns along the arterial.

[ErmineNotyours]

Flashing red arrows, Bellingham, Washington

[jakeroot]

Flashing red arrows, Bellingham, Washington

But no indication (approaching from the opposite direction) that this approach has a stop sign. I don't get it.

[bcroadguy]

Yellow signals? In California?
https://www.google.com/maps/@37.7030995,-122.4858098,3a,39.2y,334.05h,97.04t/data=!3m6!1e1!3m4!1s7R2T3iUgvaDP-fmGCg2UYw!2e0!7i16384!8i8192

I'm not sure if other cities in California do the same, but Long Beach has yellow bike signals:
https://www.google.com/maps/@33.7693271,-118.1876992,3a,71.4y,84.23h,93.4t/data=!3m6!1e1!3m4!1sMEB50AAWkxYUzRcDzA5cqg!2e0!7i16384!8i8192

[jeffandnicole]

Flashing red arrows, Bellingham, Washington

But no indication (approaching from the opposite direction) that this approach has a stop sign. I don't get it.

There's a stop sign here approaching in this direction: https://goo.gl/maps/txhySnsMf1gXRN4w8

In the opposing direction, along with the cross street, they both have traffic lights.  So in effect, the direction with the right flashing red arrows is saying you gotta stop, then you can go when safe.  For the other 2 directions, you have the right of way when it's green. 

Why can't the direction with the flashing red arrows turn left though just have a regular traffic light, and have the option to turn left...just like at any other conventional intersection?

[mrsman]

Flashing red arrows, Bellingham, Washington

But no indication (approaching from the opposite direction) that this approach has a stop sign. I don't get it.

There's a stop sign here approaching in this direction: https://goo.gl/maps/txhySnsMf1gXRN4w8

In the opposing direction, along with the cross street, they both have traffic lights.  So in effect, the direction with the right flashing red arrows is saying you gotta stop, then you can go when safe.  For the other 2 directions, you have the right of way when it's green. 

Why can't the direction with the flashing red arrows turn left though just have a regular traffic light, and have the option to turn left...just like at any other conventional intersection?

The only thing I can think of is that since there is only one lane on Holly, they don't want traffic backed up with a car making a left that can block the traffic behind it.  From looking at a map of the area, it seems like Holly is a relatively important street and most southbound traffic will make a right on Bay and then a left on Chestnut to continue in that direction.

The only question I have is why is it allowed (or if allowed why is it a good idea) to have a stop sign when the three other directions are controlled by signal?  I can see imposing something along the lines of a solid red when Bay has green, which is a normal turn, and then maybe a flashing yellow arrow when Holly northbound has green to encourage yielding to pedestrians (and maybe yielding as well to Holly traffic that turns left onto Bay).  A single cyclops flashing red arrow does not provide the nuance of letting drivers on southbound Holly know what signal cross traffic and opposing traffic is facing.

[ErmineNotyours]

Saw these on display at the Big Top Curiosity Shop in South Park, Seattle.  Somebody preserved some of the really old incandescent ped signals Seattle used to use and which I thought were gone forever.

[jakeroot]

Saw these on display at the Big Top Curiosity Shop in South Park, Seattle.  Somebody preserved some of the really old incandescent ped signals Seattle used to use and which I thought were gone forever.

https://live.staticflickr.com/65535/49782663928_b7c6732411_z.jpg

Odd that they are switched? Maybe that was the norm or no one cared?

There is something beautifully elegant about round pedestrian signals. Really too bad they aren't more common now. I think there are a few examples left in the US (somewhere in Florida, IIRC), but they are exceptionally rare. Perhaps extinct in the wild at this point.

[jakeroot]

Could anyone make sense of this signal in Grapevine, Texas?...

https://goo.gl/maps/oSQHHPm4wyXLsYC79

5-section tower, but the solid green is on the bottom lens rather than center. Both directions along Hwy 26.

It's almost like they took the regular 5-section horizontal signal (where the solid green is on the far-right), and flipped it 90-degrees clockwise.

[fwydriver405]

So I wonder what the purpose of these PV signals facing the wrong direction on the Malden Bridge on Route 99 in Boston/Everett... it looks like at one time they were used when all traffic was shifted on the other deck but now it looks like they just stay dormant.

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2

[jakeroot]

So I wonder what the purpose of these PV signals facing the wrong direction on the Malden Bridge on Route 99 in Boston/Everett... it looks like at one time they were used when all traffic was shifted on the other deck but now it looks like they just stay dormant.

1
2

At least for the second link, it looks plenty visible when approaching the bridge. Maybe it was just meant to be a supplemental signal? Not used to seeing them placed like that, to be fair.

[mrsman]

So I wonder what the purpose of these PV signals facing the wrong direction on the Malden Bridge on Route 99 in Boston/Everett... it looks like at one time they were used when all traffic was shifted on the other deck but now it looks like they just stay dormant.

1
2

I would agree.  Perhaps, they know that there are occasions when one side is closed, so the other is used for two-way traffic, yet we still have to stop traffic when the drawbridge is opened.

[jakeroot]

So I wonder what the purpose of these PV signals facing the wrong direction on the Malden Bridge on Route 99 in Boston/Everett... it looks like at one time they were used when all traffic was shifted on the other deck but now it looks like they just stay dormant.

1
2

I would agree.  Perhaps, they know that there are occasions when one side is closed, so the other is used for two-way traffic, yet we still have to stop traffic when the drawbridge is opened.

I don't think this is the case. The signals are only visible when on the correct side of the road. If the signals were for contraflow, the signal should be visible when the street view camera is turned around, but it's not. The signal is only visible to traffic proceeding in the correct direction. Ergo, it's almost certainly just a supplemental signal. A weird one, sure, but still more likely than for contraflow situations, since, as I just said, it wouldn't be visible when driving "the wrong way".

[mrsman]

So I wonder what the purpose of these PV signals facing the wrong direction on the Malden Bridge on Route 99 in Boston/Everett... it looks like at one time they were used when all traffic was shifted on the other deck but now it looks like they just stay dormant.

1
2

I would agree.  Perhaps, they know that there are occasions when one side is closed, so the other is used for two-way traffic, yet we still have to stop traffic when the drawbridge is opened.

I don't think this is the case. The signals are only visible when on the correct side of the road. If the signals were for contraflow, the signal should be visible when the street view camera is turned around, but it's not. The signal is only visible to traffic proceeding in the correct direction. Ergo, it's almost certainly just a supplemental signal. A weird one, sure, but still more likely than for contraflow situations, since, as I just said, it wouldn't be visible when driving "the wrong way".

The signal head is visible in the contraflow direction, just off.  (at least that's what it looks like to me).

Of course, the signal will only be placed ahead of the drawbridge, as there is no point in stopping traffic coming off the drawbridge.



Here is another example of a contraflow drawbridge signal, in Hampton Roads VA.  (Looks like it also has the function of lane control as the contraflow signals are red).


https://lh4.googleusercontent.com/-eaPYErcRFIY/UM8-e-x96-I/AAAAAAAAEpU/RJbR0OL1Ejc/s640/IMG_0431.JPG
https://lh6.googleusercontent.com/-W7r9GysancI/UM8-fFKSvQI/AAAAAAAAEpk/v0N6C6yTYjw/s640/IMG_0432.JPG
https://lh4.googleusercontent.com/-kXWLxv2Ch00/UM8-gc6HF5I/AAAAAAAAEp4/7GQFK1rk7bs/s640/IMG_0441.JPG



The opposite-facing signals on the other carriageway are for contraflow situations, such as a hurricane evacuation.

https://lightsflashingbright.blogspot.com/2012/12/?m=0

[CJResotko]

Could anyone make sense of this signal in Grapevine, Texas?...

https://goo.gl/maps/oSQHHPm4wyXLsYC79

5-section tower, but the solid green is on the bottom lens rather than center. Both directions along Hwy 26.

It's almost like they took the regular 5-section horizontal signal (where the solid green is on the far-right), and flipped it 90-degrees clockwise.

The solid green and green arrow indications are flipped around.
https://www.google.com/maps/@32.9324197,-97.0607891,3a,47.1y,332.55h,98.93t/data=!3m7!1e1!3m5!1s5TMPddxv33E0bQOQ_OU2tg!2e0!5s20150401T000000!7i13312!8i6656

[jakeroot]

So I wonder what the purpose of these PV signals facing the wrong direction on the Malden Bridge on Route 99 in Boston/Everett... it looks like at one time they were used when all traffic was shifted on the other deck but now it looks like they just stay dormant.

1
2

I would agree.  Perhaps, they know that there are occasions when one side is closed, so the other is used for two-way traffic, yet we still have to stop traffic when the drawbridge is opened.

I don't think this is the case. The signals are only visible when on the correct side of the road. If the signals were for contraflow, the signal should be visible when the street view camera is turned around, but it's not. The signal is only visible to traffic proceeding in the correct direction. Ergo, it's almost certainly just a supplemental signal. A weird one, sure, but still more likely than for contraflow situations, since, as I just said, it wouldn't be visible when driving "the wrong way".

The signal head is visible in the contraflow direction, just off.  (at least that's what it looks like to me).

Of course, the signal will only be placed ahead of the drawbridge, as there is no point in stopping traffic coming off the drawbridge.
[clipped]

I see now. I got lucky and found a street view link (posted in my quote) that shows the far-left overhead signal as visible to regular traffic, alongside the other three signals, but all other street view images show it turned off.

I wonder if it was installed while they were doing construction, and thus some occasional contraflow, and just never removed it? That would line up with why the only street view imagery of it turned on, is in 2014, apparently right after construction. They possibly hadn't got around to turning it off or removing it, instead opting to just disable the signal. I can't see why there would be any need for contraflow signals along this bridge. It's not part of evacuation route (well, I don't think it is).

[roadfro]

Could anyone make sense of this signal in Grapevine, Texas?...

https://goo.gl/maps/oSQHHPm4wyXLsYC79

5-section tower, but the solid green is on the bottom lens rather than center. Both directions along Hwy 26.

It's almost like they took the regular 5-section horizontal signal (where the solid green is on the far-right), and flipped it 90-degrees clockwise.

The solid green and green arrow indications are flipped around.
https://www.google.com/maps/@32.9324197,-97.0607891,3a,47.1y,332.55h,98.93t/data=!3m7!1e1!3m5!1s5TMPddxv33E0bQOQ_OU2tg!2e0!5s20150401T000000!7i13312!8i6656

Actually, they're not. Standard order in a 5-section vertical stack for left turns:

[R]
[Y]
[G]
[<Y]
[<G]

I think Jake's right and they just used a display meant to be horizontal and rotated the arrow lenses. Standard order in a 5-section horizontal for left turns:

[R][Y][<Y][<G][G]