Signals with conflicting movements

Started by jakeroot, July 20, 2017, 06:32:59 PM

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jakeroot

In Seattle yesterday, I noticed that the left turns from NE 44 St/Walla Walla Road onto Montlake Blvd conflict with each other.

I'm normally all for permissive left turns, but they don't work when the left turns overlap (except when there's a wide median, and left turns happen behind you).

Here's an illustration of the intersection with the problems:



And here's a video of me going through the intersection yesterday. I discovered the issue when I went through it. Myself and the car across from me both hesitated for a moment before I just decided to go, since they clearly intended to wait...

https://youtu.be/WclqHxte6Gk

The easy fix here, in order to maintain the double left movement, would be to pull back the stop lines and repaint the guide lines. The double left has to remain due to the lack of storage space between Montlake and NE 25 Ave.


cl94

Oh, boy. In New York, a case like that would almost certainly have split phasing. I know of several places with left turn paths that overlap or come close to it and phasing is split or lead-lag (latter typically the case if the movements are from a major road and there are no option lanes).
Please note: All posts represent my personal opinions and do not represent those of my employer or any of its partner agencies.

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jakeroot

Quote from: cl94 on July 20, 2017, 06:44:06 PM
Oh, boy. In New York, a case like that would almost certainly have split phasing. I know of several places with left turn paths that overlap or come close to it and phasing is split or lead-lag (latter typically the case if the movements are from a major road and there are no option lanes).

In my experience, an intersection setup like this would have split phasing here as well. The fact that it isn't split phased is quite surprising. I feel like an error was made somewhere.

Seattle has several double lefts without any protected phasing. The rest work just fine. And even this one seems to work okay. It's just awkward since you have to look at the other driver, and decide who goes first.

Big John

Quote from: jakeroot on July 20, 2017, 06:32:59 PM
In Seattle yesterday, I noticed that the left turns from NE 44 St/Walla Walla Road onto Montlake Blvd conflict with each other.

I'm normally all for permissive left turns, but they don't work when the left turns overlap (except when there's a wide median, and left turns happen behind you).

Here's an illustration of the intersection with the problems:




The easy fix here, in order to maintain the double left movement, would be to pull back the stop lines and repaint the guide lines. The double left has to remain due to the lack of storage space between Montlake and NE 25 Ave.
I don't like the way the guide lines are painted.  It can easily be pulled away from the conflicting movement without moving the stop line.

cl94

That's the kind of situation where I'd write to DPW. It would be one thing if one of the turns clearly had priority. Here, neither does. Is the dual left turn needed? The easiest fix would be dumping that.

The closest thing to that I can think of around here is probably this intersection at US 9 and NY 7. Lefts from the east/west overlap and those movements are split phased. In this intersection along NY 7, the E/W lefts are lead-lag (EB lead, WB lag) with split north/south movements. While uncommon in most of the state, the 5-phase setup here or something similar to it is very common in NYSDOT Region 1 (and actually works quite well). The intersection immediately to the north of the first one has lead-lag for both approaches, as all left-turn lanes overlap.
Please note: All posts represent my personal opinions and do not represent those of my employer or any of its partner agencies.

Travel Mapping (updated weekly)

jakeroot

#5
Quote from: Big John on July 20, 2017, 08:16:57 PM
Quote from: jakeroot on July 20, 2017, 06:32:59 PM
In Seattle yesterday, I noticed that the left turns from NE 44 St/Walla Walla Road onto Montlake Blvd conflict with each other.

I'm normally all for permissive left turns, but they don't work when the left turns overlap (except when there's a wide median, and left turns happen behind you).

Here's an illustration of the intersection with the problems:

http://i.imgur.com/7zHYj0E.png

The easy fix here, in order to maintain the double left movement, would be to pull back the stop lines and repaint the guide lines. The double left has to remain due to the lack of storage space between Montlake and NE 25 Ave.

I don't like the way the guide lines are painted.  It can easily be pulled away from the conflicting movement without moving the stop line.

That's kind of what I was getting at with "repaint the guide lines". Right now, they, basically, encourage conflict. Pulling back the stop lines would make it even better.

jakeroot

Quote from: cl94 on July 20, 2017, 08:18:44 PM
That's the kind of situation where I'd write to DPW. It would be one thing if one of the turns clearly had priority. Here, neither does. Is the dual left turn needed? The easiest fix would be dumping that.

Most of me really wants to write to them, but I'm afraid they'll ruin it by just changing the intersection to split-phasing. Which is fine, but just repainting the lines is all you really have to do.

The double left is needed due to the lack of storage space between Montlake and NE 25 Ave, and the left is by far the most popular movement coming off of NE 44 St.

Quote from: cl94 on July 20, 2017, 08:18:44 PM
The closest thing to that I can think of around here is probably this intersection at US 9 and NY 7. Lefts from the east/west overlap and those movements are split phased. In this intersection along NY 7, the E/W lefts are lead-lag (EB lead, WB lag) with split north/south movements. While uncommon in most of the state, the 5-phase setup here or something similar to it is very common in NYSDOT Region 1 (and actually works quite well). The intersection immediately to the north of the first one has lead-lag for both approaches, as all left-turn lanes overlap.

Lead/lag with overlapping lefts is very common in Vancouver, BC. Damn near every suburban intersection with double lefts features a "DELAYED" plaque indicating as much.

That said, I was looking more for examples where the movement through the intersection, and the signal being presented to the driver, conflicts with another equal movement (such as an overlapping left turn with equal permissible phasing). I assume this is rather rare. I'll change the thread title to make this clearer (since overlapping movements are quite common).

roadfro

Quote from: jakeroot on July 20, 2017, 08:40:38 PM
Quote from: Big John on July 20, 2017, 08:16:57 PM
Quote from: jakeroot on July 20, 2017, 06:32:59 PM
In Seattle yesterday, I noticed that the left turns from NE 44 St/Walla Walla Road onto Montlake Blvd conflict with each other.

I'm normally all for permissive left turns, but they don't work when the left turns overlap (except when there's a wide median, and left turns happen behind you).

Here's an illustration of the intersection with the problems:

http://i.imgur.com/7zHYj0E.png

The easy fix here, in order to maintain the double left movement, would be to pull back the stop lines and repaint the guide lines. The double left has to remain due to the lack of storage space between Montlake and NE 25 Ave.

I don't like the way the guide lines are painted.  It can easily be pulled away from the conflicting movement without moving the stop line.

That's kind of what I was getting at with "repaint the guide lines". Right now, they, basically, encourage conflict. Pulling back the stop lines would make it even better.

But can the cat tracks and/or stop line be adjusted and still accommodate the turning movements of the appropriate design vehicle (say, a semi)?

Seems like a situation where split phasing would be better.


There are many intersections where opposing dual left turn movements would have overlapping/conflicting paths if they were to be given green at the same time. These are always run in a lead-lag fashion (which is better for signal coordination anyway).
Roadfro - AARoads Pacific Southwest moderator since 2010, Nevada roadgeek since 1983.

KEK Inc.

lol Seattle. 

I don't remember that being too much of a problem when I lived on campus.  Fortunately, there's rarely traffic coming out of the E1 parking lot most of the time, and most of the lights in the area are police overridden during events. 
Take the road less traveled.

jeffandnicole

Actually, I didn't see the opposing traffic move at all.  Are you sure this isn't already split phased?

The fact that you didn't have any left turn arrows is annoying, although this has been a typical split phase setup at many NJ traffic lights forever.  You don't realize it's split phased unless you are very familiar with the intersection because there's no indication of such split phasing.



jeffandnicole

Quote from: jeffandnicole on July 21, 2017, 06:08:15 AM
Actually, I didn't see the opposing traffic move at all.  Are you sure this isn't already split phased?

The fact that you didn't have any left turn arrows is annoying, although this has been a typical split phase setup at many NJ traffic lights forever.  You don't realize it's split phased unless you are very familiar with the intersection because there's no indication of such split phasing.

I stand corrected.  This GSV clearly shows both directions have a green light at the same time!  https://goo.gl/maps/bLab9ZW8WL92

jakeroot

#11
Quote from: roadfro on July 21, 2017, 04:54:40 AM
Quote from: jakeroot on July 20, 2017, 08:40:38 PM
Quote from: Big John on July 20, 2017, 08:16:57 PM
Quote from: jakeroot on July 20, 2017, 06:32:59 PM
In Seattle yesterday, I noticed that the left turns from NE 44 St/Walla Walla Road onto Montlake Blvd conflict with each other.

I'm normally all for permissive left turns, but they don't work when the left turns overlap (except when there's a wide median, and left turns happen behind you).

Here's an illustration of the intersection with the problems:

http://i.imgur.com/7zHYj0E.png

The easy fix here, in order to maintain the double left movement, would be to pull back the stop lines and repaint the guide lines. The double left has to remain due to the lack of storage space between Montlake and NE 25 Ave.

I don't like the way the guide lines are painted.  It can easily be pulled away from the conflicting movement without moving the stop line.

That's kind of what I was getting at with "repaint the guide lines". Right now, they, basically, encourage conflict. Pulling back the stop lines would make it even better.

But can the cat tracks and/or stop line be adjusted and still accommodate the turning movements of the appropriate design vehicle (say, a semi)?

Seems like a situation where split phasing would be better.

I suspect the new design would still be able to accommodate large vehicles. If anything, the less sharp left turn would be better for trucks.

Split phase would be better, yes. But it seems like an obvious cheap fix, and I'm sure there's a better way to go about improving this intersection.

After studying the area, I think banning left turns might better (coming from the E1 parking lot). There's an entrance onto Montlake on the otherside of the parking lot. This left turn is basically a duplicate of that movement.

jakeroot

Quote from: KEK Inc. on July 21, 2017, 05:55:59 AM
lol Seattle. 

I don't remember that being too much of a problem when I lived on campus.  Fortunately, there's rarely traffic coming out of the E1 parking lot most of the time, and most of the lights in the area are police overridden during events.

I've gone through the intersection on many occasions (mostly just farting around). It never occurred to me how bad the left turn overlap was until I finally had an oncoming car that was also turning left. Hence this post only now.

freebrickproductions

This intersection here in Huntsville appears to have had the same issue:
https://www.google.com/maps/@34.6466822,-86.5654093,56m/data=!3m1!1e3

However, the city recently went and made Blanda Drive split-phased, eliminating any potential issues, even through Blanda Drive doesn't get much northbound traffic at the intersection.
It's all fun & games until someone summons Cthulhu and brings about the end of the world.

I also collect traffic lights, road signs, fans, and railroad crossing equipment.

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jakeroot

Quote from: freebrickproductions on July 22, 2017, 12:35:14 PM
This intersection here in Huntsville appears to have had the same issue:
https://www.google.com/maps/@34.6466822,-86.5654093,56m/data=!3m1!1e3

However, the city recently went and made Blanda Drive split-phased, eliminating any potential issues, even through Blanda Drive doesn't get much northbound traffic at the intersection.

That does appear to be a very similar setup. The overlap doesn't seem to be quite as bad as my first example, but there definitely appears to be some.

Huntsville seems to have quite a few double lefts with permissive phasing.

freebrickproductions

Quote from: jakeroot on July 22, 2017, 01:03:37 PM
Quote from: freebrickproductions on July 22, 2017, 12:35:14 PM
This intersection here in Huntsville appears to have had the same issue:
https://www.google.com/maps/@34.6466822,-86.5654093,56m/data=!3m1!1e3

However, the city recently went and made Blanda Drive split-phased, eliminating any potential issues, even through Blanda Drive doesn't get much northbound traffic at the intersection.

That does appear to be a very similar setup. The overlap doesn't seem to be quite as bad as my first example, but there definitely appears to be some.

Huntsville seems to have quite a few double lefts with permissive phasing.
Yea, but I don't mind. Most of them are on not-as-busy roads so there's never really much of an issue. What you rarely see however is a shared protected/permissive left turn at an intersection. The only two I'm aware of in the city are at these intersections:
https://www.google.com/maps/@34.7341689,-86.5879301,3a,60y,73.63h,78.68t/data=!3m6!1e1!3m4!1sqKpel5IEAH23YsysWkGH6g!2e0!7i13312!8i6656

https://www.google.com/maps/@34.7127027,-86.5749842,3a,35.7y,107.79h,86.48t/data=!3m6!1e1!3m4!1sJut2TQakmXcgqFIr2g29JA!2e0!7i13312!8i6656

Of course, in both cases, the opposing movement isn't allowed to turn left at the intersection, so split-phasing wouldn't work too well there.
It's all fun & games until someone summons Cthulhu and brings about the end of the world.

I also collect traffic lights, road signs, fans, and railroad crossing equipment.

(They/Them)

jakeroot

Quote from: freebrickproductions on July 22, 2017, 08:42:22 PM
Quote from: jakeroot on July 22, 2017, 01:03:37 PM
Quote from: freebrickproductions on July 22, 2017, 12:35:14 PM
This intersection here in Huntsville appears to have had the same issue:
https://www.google.com/maps/@34.6466822,-86.5654093,56m/data=!3m1!1e3

However, the city recently went and made Blanda Drive split-phased, eliminating any potential issues, even through Blanda Drive doesn't get much northbound traffic at the intersection.

That does appear to be a very similar setup. The overlap doesn't seem to be quite as bad as my first example, but there definitely appears to be some.

Huntsville seems to have quite a few double lefts with permissive phasing.
Yea, but I don't mind. Most of them are on not-as-busy roads so there's never really much of an issue. What you rarely see however is a shared protected/permissive left turn at an intersection. The only two I'm aware of in the city are at these intersections:
https://www.google.com/maps/@34.7341689,-86.5879301,3a,60y,73.63h,78.68t/data=!3m6!1e1!3m4!1sqKpel5IEAH23YsysWkGH6g!2e0!7i13312!8i6656

https://www.google.com/maps/@34.7127027,-86.5749842,3a,35.7y,107.79h,86.48t/data=!3m6!1e1!3m4!1sJut2TQakmXcgqFIr2g29JA!2e0!7i13312!8i6656

Of course, in both cases, the opposing movement isn't allowed to turn left at the intersection, so split-phasing wouldn't work too well there.

Split phasing [with an option lane] when the opposite direction does not permit turns is moronic. I know of some places that seem to do it more often than others (Australia and New Zealand). Seattle's only double left FYA is on to a one way, and it involves a shared left/straight lane.

Jet380

Quote from: jakeroot on July 22, 2017, 09:34:14 PM
Split phasing [with an option lane] when the opposite direction does not permit turns is moronic. I know of some places that seem to do it more often than others (Australia and New Zealand).
I've only just started noticing these in Perth and it makes me want to tear my hair out every time I'm stopped at one  :banghead:

US 89

I thought that any intersections with a shared left/straight lane had to be split phased. I'm really surprised this one isn't, as I've never seen an exception to this rule.

jakeroot

Quote from: roadguy2 on July 31, 2017, 12:37:10 AM
I thought that any intersections with a shared left/straight lane had to be split phased. I'm really surprised this one isn't, as I've never seen an exception to this rule.

Definitely not true, at least when there's a single left-turning lane. More often true when there's two left turn lanes (one dedicated left plus one shared left), but still not always the case (see list below). No agency, to my knowledge, requires split phasing when there's a single option lane. Quite a few, however, opt for some level of protected phasing when there's an accompanying left-turn-only lane alongside the shared left/straight lane (effectively a double left).

Examples of double permissive turns with shared left/straight lanes:

Seattle: James St @ 6 Ave: https://goo.gl/d86Z8J (note improper use of FYA despite shared left/straight lane)
Seattle: 7 Ave @ Madison St: https://goo.gl/Ri1tEw
Seattle: 5 Ave @ Mercer St: https://goo.gl/mAobYB (formerly -- now single protected left)
Seattle: NE 44 St @ Montlake Blvd: https://goo.gl/Kt1sfJ (example in the video above)
Vancouver, BC: Cambie St @ SW Marine Dr: https://goo.gl/RN3pA9
Vancouver, BC: Main St @ the Dunsmuir Viaduct: https://goo.gl/97bw3W
Vancouver, BC: Denman St @ W Georgia St: https://goo.gl/i9frHB

As for permissive single-lane shared left/straight lanes, look up and down almost any major N/S or E/W arterial road in Vancouver, and you'll see a bunch (and I mean a bunch). Vancouver seems to be renowned in the roadgeek world for their total lack of dedicated turn lanes along much of their arterial road network.

US 89

Maybe it's just a Utah thing. But around here, any intersection with a shared left-straight lane is split phased. Even minor side streets are often split phased if a majority of traffic is turning right, since this often requires one dedicated right turn and one straight/left lane.

It makes sense. If there is a left turning car in a shared left-straight lane, and the light isn't split phased, the through traffic would get stuck behind (and quite annoyed at) the left turning car who is waiting for a gap in oncoming traffic.

jakeroot

Quote from: roadguy2 on July 31, 2017, 03:09:44 PM
Maybe it's just a Utah thing. But around here, any intersection with a shared left-straight lane is split phased. Even minor side streets are often split phased if a majority of traffic is turning right, since this often requires one dedicated right turn and one straight/left lane.

An example of what you described near me, with fully-permissive phasing (plus a right turn filter): https://goo.gl/gqcTe3 -- Continue below....

Quote from: roadguy2 on July 31, 2017, 03:09:44 PM
It makes sense. If there is a left turning car in a shared left-straight lane, and the light isn't split phased, the through traffic would get stuck behind (and quite annoyed at) the left turning car who is waiting for a gap in oncoming traffic.

That's understandable, but how often in these situations does the oncoming traffic occupy the intersection for the entire length of the cycle? In the intersection above (one I go through quite a lot), there is only a car coming the other direction about every other time I approach it. And more often than not, they're turning left. As I always turn left here, I just turn at the same time as the other car, and if there's a car behind each of us, they can either continue straight at the same time, or also turn next to each other. I can only think of one occasion when I didn't make a light, and it was because of pedestrian activity that prevented more than a couple of cars from turning at once.

WSDOT recently re-worked an intersection near Snohomish, WA (164 St SE @ Hwy 9). Because the side street had no turn lanes, they decided that split-phasing would be best. But it quickly became apparent after installing the signal that the split phasing took up too much time, and was creating severe congestion along Hwy 9. Several months ago, they changed 164 St to fully permissive, and changed the left turn phasing along Hwy 9 from protected-only to FYAs. The intersection flows much better now, due to the much shorter signal phase required to let traffic from 164 St continue on their way.

Here's a link to the press release that details the change: https://goo.gl/vTER5t (see "Changes at key intersections")...

Quote
Eastbound and westbound traffic on 164th Street Southeast will now travel at the same time through the intersection, rather than one side at a time that occurs today. Additionally, a new flashing yellow arrow will allow northbound and southbound drivers on SR 9 to make a left turn during gaps in oncoming traffic. These traffic signal cycle changes will increase the green light time traffic on SR 9 and reduce backups.

Scott5114

Quote from: jakeroot on July 20, 2017, 08:55:13 PM
Quote from: cl94 on July 20, 2017, 08:18:44 PM
That's the kind of situation where I'd write to DPW. It would be one thing if one of the turns clearly had priority. Here, neither does. Is the dual left turn needed? The easiest fix would be dumping that.

Most of me really wants to write to them, but I'm afraid they'll ruin it by just changing the intersection to split-phasing. Which is fine, but just repainting the lines is all you really have to do.

It would be better than waiting until someone gets hurt.
uncontrollable freak sardine salad chef

US 89

#23
Quote from: jakeroot on July 31, 2017, 05:43:27 PM
Quote from: roadguy2 on July 31, 2017, 03:09:44 PM
It makes sense. If there is a left turning car in a shared left-straight lane, and the light isn't split phased, the through traffic would get stuck behind (and quite annoyed at) the left turning car who is waiting for a gap in oncoming traffic.

That's understandable, but how often in these situations does the oncoming traffic occupy the intersection for the entire length of the cycle? In the intersection above (one I go through quite a lot), there is only a car coming the other direction about every other time I approach it. And more often than not, they're turning left. As I always turn left here, I just turn at the same time as the other car, and if there's a car behind each of us, they can either continue straight at the same time, or also turn next to each other. I can only think of one occasion when I didn't make a light, and it was because of pedestrian activity that prevented more than a couple of cars from turning at once.

Most of the split-phased intersections are fairly busy around here, since there was enough turning traffic to justify the arrangement. Here are/were a few in my area off the top of my head (some have been replaced) and the likely reason for them being split phased:

State St/N. Temple, SLC. High volume of traffic turning west from northbound State.
600 N/400 W, SLC. High traffic volume of traffic turning west from northbound 400 W. (The intersection was reconfigured to a dual left in 2016).
Columbus St/500 N, SLC. High volume of traffic turning north from westbound 500 N.
US 89/Harrison Blvd, Ogden. High volume of traffic turning east from southbound Harrison. (This intersection was moved and replaced with a triple left turn in 2015).

jakeroot

Quote from: Scott5114 on August 01, 2017, 05:50:05 AM
Quote from: jakeroot on July 20, 2017, 08:55:13 PM
Quote from: cl94 on July 20, 2017, 08:18:44 PM
That's the kind of situation where I'd write to DPW. It would be one thing if one of the turns clearly had priority. Here, neither does. Is the dual left turn needed? The easiest fix would be dumping that.

Most of me really wants to write to them, but I'm afraid they'll ruin it by just changing the intersection to split-phasing. Which is fine, but just repainting the lines is all you really have to do.

It would be better than waiting until someone gets hurt.

I think I may write to them and ask for them to change the E1 lot exit to not allow left turns. There's an exit towards Montlake from the south side of the parking lot, so the left turn here is redundant anyway.



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