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Double left turns with permissive phasing

Started by jakeroot, December 14, 2015, 02:01:17 AM

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Do you think dual permissive turns should be allowed?

Yes
57 (50.4%)
No
35 (31%)
Cat
21 (18.6%)

Total Members Voted: 113

betfourteen



jakeroot

#501
And again in Nassau County: Fortunoff Way @ Old Country Rd

(I feel like someone posted this already, but I cannot confirm)


See reply #535

jeffandnicole

Quote from: betfourteen on March 17, 2021, 03:20:01 PM
Hello again Nassau County - https://goo.gl/maps/yw3BUwhuvEWp9q4C7
Quote from: jakeroot on March 19, 2021, 01:46:20 PM
And again in Nassau County: Fortunoff Way @ Old Country Rd

(I feel like someone posted this already, but I cannot confirm)

These shouldn't be permissive phasing as they aren't true double lefts.  With the dual left/thru lane, they should only be split phasing.

jakeroot

Quote from: jeffandnicole on March 19, 2021, 01:53:19 PM
Quote from: betfourteen on March 17, 2021, 03:20:01 PM
Hello again Nassau County - https://goo.gl/maps/yw3BUwhuvEWp9q4C7
Quote from: jakeroot on March 19, 2021, 01:46:20 PM
And again in Nassau County: Fortunoff Way @ Old Country Rd

(I feel like someone posted this already, but I cannot confirm)

These shouldn't be permissive phasing as they aren't true double lefts.  With the dual left/thru lane, they should only be split phasing.

Split-phasing is usually used in these circumstances because of policy, not because it actually needs to be split-phased for safety's sake or whatever.

betfourteen

Quote from: jakeroot on March 19, 2021, 01:46:20 PM
And again in Nassau County: Fortunoff Way @ Old Country Rd

(I feel like someone posted this already, but I cannot confirm)

Yes, #535 ... From yours truly

jakeroot

Quote from: betfourteen on March 19, 2021, 02:13:23 PM
Quote from: jakeroot on March 19, 2021, 01:46:20 PM
And again in Nassau County: Fortunoff Way @ Old Country Rd

(I feel like someone posted this already, but I cannot confirm)

Yes, #535 ... From yours truly

Thank you. I edited my post.

HTM Duke

Apologies if I'm mistaken, but I believe I've found Virginia's first entry into this category, at the intersection of Reservoir St at MLK Jr Way in Harrisonburg.  No doubt this only happened because of Harrisonburg's incorporated city status.  While the arrows aren't clearly visible in Streetview (though zooming in on the signal faces shows hints of them), I was in Harrisonburg last week and saw the setup in action.

https://goo.gl/maps/St4ph4AKxskVUDuq5
List of routes: Traveled | Clinched

jakeroot

Quote from: HTM Duke on May 18, 2021, 08:52:05 PM
Apologies if I'm mistaken, but I believe I've found Virginia's first entry into this category, at the intersection of Reservoir St at MLK Jr Way in Harrisonburg.  No doubt this only happened because of Harrisonburg's incorporated city status.  While the arrows aren't clearly visible in Streetview (though zooming in on the signal faces shows hints of them), I was in Harrisonburg last week and saw the setup in action.

https://goo.gl/maps/St4ph4AKxskVUDuq5

That's neat! Very unique setup too, given how they built it out of an old oncoming lane. Must be some serious left turn traffic.

It's not the only permissive double left in Virginia, but it's one of maybe two; there is another onto a freeway somewhere in the state.

Amtrakprod

Roadgeek, railfan, and crossing signal fan. From Massachusetts, and in high school. Youtube is my website link. Loves FYAs signals. Interest in Bicycle Infrastructure. Owns one Leotech Pedestrian Signal, and a Safetran Type 1 E bell.

jakeroot

Quote from: Amtrakprod on June 12, 2021, 10:44:29 PM
Columbus: https://www.google.com/maps/@39.9591571,-82.9969848,3a,31.6y,263.21h,84.49t/data=!3m6!1e1!3m4!1so8qZuLlXT8fQgnGq4iJXHA!2e0!7i16384!8i8192!5m1!1e3

Great use case for a permissive left with two lanes. Since I'm coming traffic is a minor driveway, there's really no reason to split-phase. It would be especially stupid since it's a one-way street, and split-phasing would completely block through traffic despite not having any oncoming lefts. Not that there would be much anyway.

Ned Weasel

"I was raised by a cup of coffee." - Strong Bad imitating Homsar

Disclaimer: Views I express are my own and don't reflect any employer or associated entity.

jakeroot

Quote from: stridentweasel on July 01, 2021, 06:46:50 PM
I finally saw a modern local one, complete with FYAs: https://goo.gl/maps/cHRTRxb4Y68qZs5Q6

Nice find! Would have loved to see a third FYA signal on the far left mast, but I get the feeling such signals are not so common in Kansas.

I appreciate that people continue to keep their eye out for these.

roadfro

#512
I'm currently in Denver for a few days. While driving about yesterday, I encountered one of these on SW-bound Wewatta at Speer Blvd (sorry, posting on phone and couldn't easily get a Street View link). Two full turn lanes with FYA displays, despite it seeming that much of the Denver area still uses offset doghouses for PPLT displays.

EDIT: Looks like there's also one in the opposite direction.
Roadfro - AARoads Pacific Southwest moderator since 2010, Nevada roadgeek since 1983.

jakeroot

#513
Quote from: roadfro on July 02, 2021, 07:39:54 PM
I'm currently in Denver for a few days. While driving about yesterday, I encountered one of these on SW-bound Wewatta at Speer Blvd (sorry, posting on phone and couldn't easily get a Street View link). Two full turn lanes with FYA displays, despite it seeming that much of the Denver area still uses offset doghouses for PPLT displays.

EDIT: Looks like there's also one in the opposite direction.

Oh, yeah. Colorado is full of these. In fact, as far as I know, CDOT is the only agency that doesn't seem to regularly install them. Pretty much every city in Colorado has double permissive lefts, with many transitioning to FYAs over the last ten years. The only rule of thumb seems to be protected-only when the double left is extremely busy, or if there are more than two left turn lanes.

jakeroot

Slight bump to refer to an old post:

Quote from: fwydriver405 on April 02, 2020, 02:29:32 PM
Quote from: mrsman on April 02, 2020, 01:15:18 PM
Quote from: deathtopumpkins on April 02, 2020, 09:25:57 AM
IMHO California has way too many protected lefts to ever rank first.

Correct, only first in signal placement.  Near dead last in signal operation.

Found this one in Downtown San Francisco (option lane). The left lane can choose between I-80 E or Bryant St, and the middle to Bryant St or continue straight to 5th St. Many drivers I've seen during rush hour, use the middle lane to turn onto I-80 E...

I believe there's another one somewhere in SF but not sure where.

EDIT: A few more -
Van Ness and Broadway (albeit temporary? - 2 left turn lanes converted from left + option)
Sloat Blvd and 19th Ave (left + option)

For some reason, this intersection (Sloat/19th) came up again in another circle, and so I did a little research this time around.

I found this article from SFGate that talks a bit more about the history of the intersection.

Prior to 2007, the double left turn (with the optional left/straight lane) had existed but it was fully permissive, no arrows. It seems to have been installed decades ago.

In 2007, the extra protected green arrow was added. It seems to operate for only a few seconds at the end of the cycle to clear any waiting traffic. According to the article, this addition of a green arrow took seven years to come to fruition. Both Sloat and 19th are state highways, so Caltrans had to approve the signal changes.

This alone really isn't surprising; cities often have to seek state approval for changes to state highways within their jurisdictions (though certainly not always). What's funny to me is, hearing that, I'm sort of staggered that Caltrans would allow San Francisco to continue operating it with a permissive double left. Based on the seven year delay, I have to assume Caltrans wanted San Francisco to simply switch it to full-time double left with fully-protected phasing, but the city seems to have been firmly against such plans, as evidenced by the current double permissive left turn.

Caltrans is quite well known for being extremely conservative with their signalization practices. Permissive lefts of any sort are hard to come by along state highways. So to think they eventually "gave their blessing" to a double permissive left is pretty nuts. Of course, this approval happened twice: once when the double left was installed in the 1960s (I assume it was permissive then), and then again in 2007 when the arrow was added.

mrsman

^^^^^
One more thing about this intersection, 19th/Sloat.  As it is a lagging permissive left, in order to avoid yellow trap issues, the opposing left turn (Sloat WB to 19th SB) is prohibited.  But if you look carefully at the geometry, you can see that this wasn't always the case.  This now prohibited left turn has a left turn pocket in the median.  So, presumably, before the green arrow was installed for the EB to NB movement, the WB to SB left turn was allowed and used the pocket.

jakeroot

Quote from: mrsman on July 11, 2021, 09:16:30 PM
^^^^^
One more thing about this intersection, 19th/Sloat.  As it is a lagging permissive left, in order to avoid yellow trap issues, the opposing left turn (Sloat WB to 19th SB) is prohibited.  But if you look carefully at the geometry, you can see that this wasn't always the case.  This now prohibited left turn has a left turn pocket in the median.  So, presumably, before the green arrow was installed for the EB to NB movement, the WB to SB left turn was allowed and used the pocket.

Going back in historic satellite imagery, it seems that lane has been blocked off since at least the 60s. With that double left turn, it seems visibility would have been poor enough that it was just easier to eliminate it. Seems to have been replaced by U-turn maneuver at 21st.

mrsman

Quote from: jakeroot on July 12, 2021, 02:12:59 AM
Quote from: mrsman on July 11, 2021, 09:16:30 PM
^^^^^
One more thing about this intersection, 19th/Sloat.  As it is a lagging permissive left, in order to avoid yellow trap issues, the opposing left turn (Sloat WB to 19th SB) is prohibited.  But if you look carefully at the geometry, you can see that this wasn't always the case.  This now prohibited left turn has a left turn pocket in the median.  So, presumably, before the green arrow was installed for the EB to NB movement, the WB to SB left turn was allowed and used the pocket.

Going back in historic satellite imagery, it seems that lane has been blocked off since at least the 60s. With that double left turn, it seems visibility would have been poor enough that it was just easier to eliminate it. Seems to have been replaced by U-turn maneuver at 21st.

True.  It seems that many of the permissive double lefts in CA occur in situations where the opposing left is prohibited (or at least restricted to left on arrow only).  Part of the reason is that drivers making the opposing left could advance and camp in the middle of the intersection while they wait for the gap.  This will certainly impact the visibility of traffic making the double left.

So I guess when the city decided that a double left was appropriate, they then prohibited the opposing left.  Makes sense.

kphoger

Quote from: mrsman on July 12, 2021, 10:12:03 AM
It seems that many of the permissive double lefts in CA occur in situations where the opposing left is prohibited (or at least restricted to left on arrow only).  Part of the reason is that drivers making the opposing left could advance and camp in the middle of the intersection while they wait for the gap.

I think that's a reasonable concern.
Keep right except to pass.  Yes.  You.
Visit scenic Orleans County, NY!
Male pronouns, please.

Quote from: Philip K. DickIf you can control the meaning of words, you can control the people who must use them.

Ned Weasel

Quote from: jakeroot on July 02, 2021, 01:57:17 PM
Quote from: stridentweasel on July 01, 2021, 06:46:50 PM
I finally saw a modern local one, complete with FYAs: https://goo.gl/maps/cHRTRxb4Y68qZs5Q6

Nice find! Would have loved to see a third FYA signal on the far left mast, but I get the feeling such signals are not so common in Kansas.

I appreciate that people continue to keep their eye out for these.

Oh yeah, there's another nearby: https://goo.gl/maps/W2sBPjURFyENcZyJ6

What's weird about that intersection, though, is the other direction of Strang Line Road has a protected-only signal for a single left turn: https://goo.gl/maps/gXdAG3YogLu2DRhm9
"I was raised by a cup of coffee." - Strong Bad imitating Homsar

Disclaimer: Views I express are my own and don't reflect any employer or associated entity.

jakeroot

Quote from: stridentweasel on July 21, 2021, 06:42:55 AM
Quote from: jakeroot on July 02, 2021, 01:57:17 PM
Quote from: stridentweasel on July 01, 2021, 06:46:50 PM
I finally saw a modern local one, complete with FYAs: https://goo.gl/maps/cHRTRxb4Y68qZs5Q6

Nice find! Would have loved to see a third FYA signal on the far left mast, but I get the feeling such signals are not so common in Kansas.

I appreciate that people continue to keep their eye out for these.

Oh yeah, there's another nearby: https://goo.gl/maps/W2sBPjURFyENcZyJ6

What's weird about that intersection, though, is the other direction of Strang Line Road has a protected-only signal for a single left turn: https://goo.gl/maps/gXdAG3YogLu2DRhm9

Another good find, very cool!

I've definitely seen that setup before, with a double permissive left opposing a single lane protected-only left. Pretty much all have been for one of three reasons: (1) military base gate; (2) poor visibility (maybe the reason here?); (3) not enough room to accommodate both directions waiting simultaneously (very rare -- cannot recall examples off the top of my head).

mrsman

#521
Quote from: jakeroot on July 21, 2021, 12:30:53 PM
Quote from: stridentweasel on July 21, 2021, 06:42:55 AM
Quote from: jakeroot on July 02, 2021, 01:57:17 PM
Quote from: stridentweasel on July 01, 2021, 06:46:50 PM
I finally saw a modern local one, complete with FYAs: https://goo.gl/maps/cHRTRxb4Y68qZs5Q6

Nice find! Would have loved to see a third FYA signal on the far left mast, but I get the feeling such signals are not so common in Kansas.

I appreciate that people continue to keep their eye out for these.

Oh yeah, there's another nearby: https://goo.gl/maps/W2sBPjURFyENcZyJ6

What's weird about that intersection, though, is the other direction of Strang Line Road has a protected-only signal for a single left turn: https://goo.gl/maps/gXdAG3YogLu2DRhm9

Another good find, very cool!

I've definitely seen that setup before, with a double permissive left opposing a single lane protected-only left. Pretty much all have been for one of three reasons: (1) military base gate; (2) poor visibility (maybe the reason here?); (3) not enough room to accommodate both directions waiting simultaneously (very rare -- cannot recall examples off the top of my head).

Another possibility may be signalization.  Now, this is not so common or necessary any more where FYAs are used, but in some jurisdictions there may still be fear of yellow traps and perceived yellow traps.

Let's say that we are not using FYAs (or Dallas phasing or other mechanisms to avoid yellow trap).  So if you signalize a lead-lag signal, the leading arrow must be a protected only turn, if the lagging arrow is permissive/protected, in order to avoid yellow trap.  And when you have a situation like that, it is better to make the busier of the two lefts, the lagging left so that as many people as possible  can turn left during the gaps in traffic.

Earlier, we established that for an option lane setting, it is far more desirable to signalize that as a permissive lagging left.  This is because when there are three lanes, and the left lane turns left, the right lane goes straight, and the center lane is an option lane, it provides some assurance for drivers that if they are waiting in the option lane behind someone turning left -- there will be an opportunity to proceed before the end of the phase.  The left turners can filter during the natural gaps, and of course the protected turn at the end will allow both straight and left folks the opportunity to proceed until the light turns red.

Now it is true that if you go back up this thread and you see the many examples of option lane arrangements with permissive phasing, they would primarily have a lagging left and they will also prohibit or restrict the opposing left.  A restricted left is a leading left that only allows for a protected turn.

It seems like we only discussed this a few weeks ago.  19th and Sloat in San Francisco has a lagging, permissive, option lane arrangement for the eastbound to northbound left.   Yet, there is a left turn bay for the westbound to southbound left -- a remnant of a once permitted turn before there was a double left in the opposite direction.

Let's say that SF (or Caltrans) decides that they want to reintroduce that westbound to southbound left.  The best way to do it would be a leading protected-only left, so as to not impact the visibility of the eastbound to northbound turn and to not introduce a yellow trap at the intersection.  And that would be a situation with a permissive double left, but a protected-only opposing single left.

jakeroot

#522
I'm starting to think these may actually rank as "relatively common" in New Mexico. Found two three four new examples today:

(1) Yale Blvd northbound to Gibson Blvd westbound (alt view)
(2) University Blvd northbound to Rio Bravo Blvd westbound (no opposing left)
(3) Carlisle Blvd northbound to Montgomery Blvd westbound (alt view)
(4) NM-556 westbound at I-25 southbound on-ramp (FYA) (formerly protected-only)

The second was formerly protected-only. Seems to operate with lagging phasing, based on this still.

The third has an opposing single-lane protected-only left turn. Go figure, given the discussion above. The left turn seems to be leading, so I'm not sure the purpose of the opposing protection.

US 89

I encountered one the other day from Dewar Drive eastbound to Gateway Blvd in Rock Springs, WY. First one I’d ever seen in Wyoming.

https://goo.gl/maps/6d1NqeFpcFGhXQjr6

jakeroot

Quote from: US 89 on August 12, 2021, 08:30:22 AM
I encountered one the other day from Dewar Drive eastbound to Gateway Blvd in Rock Springs, WY. First one I'd ever seen in Wyoming.

https://goo.gl/maps/6d1NqeFpcFGhXQjr6

Same here, never seen one in Wyoming.

Virtually zero historic Street View imagery, but it looks to have been installed around 2008 or 2009.



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