Double left turns with permissive phasing

[JMAN_WiS&S]

I grew up learning how to drive on the Gulf Coast in Mississippi, where there are apparently still at least three intersections with dual permissive lefts (which are at (1) Popps Ferry Rd and Cedar Lake Blvd in Biloxi, (2) MS 605 (Cowan Rd) and Pass Rd in Gulfport, and (3) WB Rodriguez St to SB I-110 in D'Iberville (see lane markings)).

Just an update. All three of the intersections you posted have been updated. Intersections one and two have been changed to protected only, whereas the third now has mast-arms with new signals (still doghouses for the double left, thank God).

In the first example, they widened Popps Ferry Road and changed the signal phasing. They could have easily aligned the WB left turn so that it was offset to the left (improving visibility for EB turning traffic). But, I guess they decided protected was good enough! Oh well.

Since then, I think the only other place I've seen them is Duluth, Minnesota, but since Minnesota is the place I think I've seen the most FYAs outside of Oregon and Washington, there are probably more lurking about.

Do you remember where this was? I've was looking at a map of Duluth, when I remembered this post. But I cannot find any dual permissive lefts in Duluth. I have seen quite a few dual FYA displays elsewhere in Minnesota IRL, but they all ran protected-only. Not sure what MnDOT policy is nowadays.

Isn't MnDOT's policy nowadays to instal 4 section FYA displays for ALL left turn signal movements, even if the signal is intended to only be operated in Protected mode?

[jakeroot]

I have seen quite a few dual FYA displays elsewhere in Minnesota IRL, but they all ran protected-only. Not sure what MnDOT policy is nowadays.

Isn't MnDOT's policy nowadays to instal 4 section FYA displays for ALL left turn signal movements, even if the signal is intended to only be operated in Protected mode?

That's what I was told in the past, but that seemed like such an odd move, I've remained sceptical.

[MCRoads]

Just decided the check the poll.

Surprisingly close.

The real surprise? 15% of those polled, picked "cat".

wtf

LOL, i did! Honestly, i did just for fun! 

[Bitmapped]

I haven't seen any examples of dual left PPLT in West Virginia, but but I like the concept and think it would work fine as long as the dual left is clearly signed and there are dashed lines through the intersection so it's super obvious what's going on.

i can think of several intersections near me where, most of the day, single lane PPLT works fine but at peak hours, dual lefts are really needed to handle the load. If you went protected-only for the dual lefts, it would increase delay for most of the day to benefit those couple hours when the dual lefts are really needed. PPLT dual left would seem to offer the best of both worlds with additional capacity and the the reduced delay that PPLT can permit.

[jakeroot]

i can think of several intersections near me where, most of the day, single lane PPLT works fine but at peak hours, dual lefts are really needed to handle the load. If you went protected-only for the dual lefts, it would increase delay for most of the day to benefit those couple hours when the dual lefts are really needed. PPLT dual left would seem to offer the best of both worlds with additional capacity and the the reduced delay that PPLT can permit.

At least one city near me has started to face this dilemma. All single-lane left turns have been converted to FYA, and while that has dramatically improved traffic, some of them don't have enough storage space. So, several major intersections have double lefts, but they're all protected-only, as is standard practice. They want to use FYAs for at least some of these double lefts, but are currently holding back until they are absolutely certain that it's the right decision.

[doorknob60]

i can think of several intersections near me where, most of the day, single lane PPLT works fine but at peak hours, dual lefts are really needed to handle the load. If you went protected-only for the dual lefts, it would increase delay for most of the day to benefit those couple hours when the dual lefts are really needed. PPLT dual left would seem to offer the best of both worlds with additional capacity and the the reduced delay that PPLT can permit.

At least one city near me has started to face this dilemma. All single-lane left turns have been converted to FYA, and while that has dramatically improved traffic, some of them don't have enough storage space. So, several major intersections have double lefts, but they're all protected-only, as is standard practice. They want to use FYAs for at least some of these double lefts, but are currently holding back until they are absolutely certain that it's the right decision.

Boise (well, I think in this case it was ITD, probably in collaboration with ACHD) recently converted a dual left turn setup to single left with FYA. It's at Broadway and Beacon. Well actually, one side of the intersection was dual left, and the other side was single left, protected only (because the opposing left turn lane blocked your view). And there are a lot of intersections in Boise and Meridian where there is room for two turn lanes, but only one of them is in use with a painted barrier where the second lane would be, with FYA. Unsure if any of those used to be protected only dual lefts.

Dual lefts are incredibly common here, and you see FYAs at almost every single left turn lane, so it will be interesting to see what happens with some of the intersections around here as traffic counts change. Dual permissive lefts could be very nice here if they ever allow them. Broadway/Beacon definitely didn't need the dual lefts, at least not now that the new Broadway Bridge opened (though this particular setup possibly pre-dates the west Parkcenter bridge which would make sense, though I'm not too familiar with Boise road history).

[jakeroot]

i can think of several intersections near me where, most of the day, single lane PPLT works fine but at peak hours, dual lefts are really needed to handle the load. If you went protected-only for the dual lefts, it would increase delay for most of the day to benefit those couple hours when the dual lefts are really needed. PPLT dual left would seem to offer the best of both worlds with additional capacity and the the reduced delay that PPLT can permit.

At least one city near me has started to face this dilemma. All single-lane left turns have been converted to FYA, and while that has dramatically improved traffic, some of them don't have enough storage space. So, several major intersections have double lefts, but they're all protected-only, as is standard practice. They want to use FYAs for at least some of these double lefts, but are currently holding back until they are absolutely certain that it's the right decision.

Boise (well, I think in this case it was ITD, probably in collaboration with ACHD) recently converted a dual left turn setup to single left with FYA. It's at Broadway and Beacon. Well actually, one side of the intersection was dual left, and the other side was single left, protected only (because the opposing left turn lane blocked your view). And there are a lot of intersections in Boise and Meridian where there is room for two turn lanes, but only one of them is in use with a painted barrier where the second lane would be, with FYA. Unsure if any of those used to be protected only dual lefts.

I'm glad to hear they didn't unnecessarily stick with the dual protected left. It's often not necessary....

Broadway/Beacon definitely didn't need the dual lefts, at least not now that the new Broadway Bridge opened.

California has a tendency to do something like this. They build/upgrade a new road, and they automatically build dual left turn lanes at all the major intersections and, of course, set them to protected-only. There are more than a few situations where double left turn lanes are desirable, but a lot of the ones I see don't need two lanes at all. What they need is a single-lane setup with protected/permissive phasing. Depending on the time of day, they can push more cars through an intersection than a double left. The problem, of course, is what to do at peak hours, when you might need more storage capacity, or there's too many oncoming cars for the permissive phase to be of any use. You could keep it as a single left, and switch to protected-only phasing, but that's effectively capping the throughput of the lane (permissive phasing at all times allows a variable amount of cars through during each phase, since some phases have more gaps than others, and sometimes, you'll get three or four cars turning after the red light (something that should always be practiced IMO)). You could also build a dual left with permanently protected phasing, but it will only be helpful during peak hours (though backups can still occur), and during off-peak hours, it's just annoying because you have to wait for a green arrow. The dual-permissive FYA is the result of this conundrum.

[roadfro]

For those agencies that are hesitant about a dual permissive left, but need the capacity of dual lefts in the peak hour: I wonder if there's a way you could program a signal and adequately sign/stripe the intersection so that the second turn lane is used only in the peak hour during protected-only mode, but leave one lane for permitted lefts during non-peak hours...

[jakeroot]

For those agencies that are hesitant about a dual permissive left, but need the capacity of dual lefts in the peak hour: I wonder if there's a way you could program a signal and adequately sign/stripe the intersection so that the second turn lane is used only in the peak hour during protected-only mode, but leave one lane for permitted lefts during non-peak hours...

There was a document produced by VDOT several years ago (I've posted the document before -- read the ITE stories on the bottom if you haven't already), where agencies wrote in about their FYA experiences. One of the ITE (Institute of Transport Engineers) members from Wilmington, NC wrote in, suggesting something like that:

For duals, we have seen permitted operation and have just discovered the NCDOT is experimenting with them.    We have one location out of 212 that we think may lend itself to this operation.    Like the previous point, rarely do we need duals in the overnight hours.  I think the technology will evolve that we can vary the duals by TOD.  Therefore the outside turn lane would run with a standard three section head and the inside with a 4 section FYA.  During times when the duals are needed, the FYA would be extinguished and full protection afforded.   Later, when appropriate the FYA activated and the outside lane closed with a blankout sign.   The three section(s) would stay red and the blankout sign would flash if the detector for that lane became active.

(I love the "one...out of 212" comment -- that's really it?!?)

Sounds rather complicated to me. As you might imagine, I'd rather just see FYA displays used for both lanes, with the roadway properly designed to accommodate both lanes yielding.

[mrsman]

Sounds rather complicated to me. As you might imagine, I'd rather just see FYA displays used for both lanes, with the roadway properly designed to accommodate both lanes yielding.

You are right.  But I think many states are too afraid to allow dual permissive turning.  In many places, it is quite common to close lanes with a red X over the lane for maintenance and similar purposes.  To save people time, it is well worth while.

[jakeroot]

Sounds rather complicated to me. As you might imagine, I'd rather just see FYA displays used for both lanes, with the roadway properly designed to accommodate both lanes yielding.

You are right.  But I think many states are too afraid to allow dual permissive turning.  In many places, it is quite common to close lanes with a red X over the lane for maintenance and similar purposes.  To save people time, it is well worth while.

The stickler in me would rather just see it done properly. Obviously, at least some of these places are considering dual permissive turns. Otherwise, they wouldn't be considering the whole "close a lane off during off-hours" solution (although that's a result of being concerned with the concept). If they just designed the left turn lanes correctly, they wouldn't need to bother with anything special.

A better idea, at least compared to the lane-closing concept, might be to just only have an FYA display over one of the lanes. Kind of like banning RTOR from the left lane of a dual right turn lane.

[roadfro]

The stickler in me would rather just see it done properly. Obviously, at least some of these places are considering dual permissive turns. Otherwise, they wouldn't be considering the whole "close a lane off during off-hours" solution (although that's a result of being concerned with the concept). If they just designed the left turn lanes correctly, they wouldn't need to bother with anything special.

A better idea, at least compared to the lane-closing concept, might be to just only have an FYA display over one of the lanes. Kind of like banning RTOR from the left lane of a dual right turn lane.

If you just had an FYA over one lane and a standard arrow setup over the other, I think you'd get lane imbalance issues. Or you'd get compliance issues in the second lane. A blank out sign to indicate the #2 lane signal is not in use during off-peak times would help inform the driver and deal with driver expectancy.

[Revive 755]

The stickler in me would rather just see it done properly. Obviously, at least some of these places are considering dual permissive turns. Otherwise, they wouldn't be considering the whole "close a lane off during off-hours" solution (although that's a result of being concerned with the concept). If they just designed the left turn lanes correctly, they wouldn't need to bother with anything special.

A better idea, at least compared to the lane-closing concept, might be to just only have an FYA display over one of the lanes. Kind of like banning RTOR from the left lane of a dual right turn lane.

If you just had an FYA over one lane and a standard arrow setup over the other, I think you'd get lane imbalance issues. Or you'd get compliance issues in the second lane.

I see the imbalance/compliance issues in Chicagoland a lot with dual rights where the inner lane is NTOR.  There's also the issue of someone using the turn lane that allows turns on red turning into the correct lane and then quickly switching to the lane the NTOR lane would have turned into, possibly cutting off the driver who used the NTOR lane and waited for the light to cycle.

Using a FYA head for the permissive-prot left turn lane and a protected only head for the other left turn lane would make it difficult to provide secondary/backup/redundant signal heads for the left turns.  IMHO it would be better to use lane control signals to close one of the left turn lanes or go to a modified version of Wisconsin's slotted left turn lanes (example on WI 50 near Kenosha) with a raised median between the two left turn lanes and gate off the closed turn lane during non-peak hours.

[jakeroot]

The stickler in me would rather just see it done properly. Obviously, at least some of these places are considering dual permissive turns. Otherwise, they wouldn't be considering the whole "close a lane off during off-hours" solution (although that's a result of being concerned with the concept). If they just designed the left turn lanes correctly, they wouldn't need to bother with anything special.

A better idea, at least compared to the lane-closing concept, might be to just only have an FYA display over one of the lanes. Kind of like banning RTOR from the left lane of a dual right turn lane.

If you just had an FYA over one lane and a standard arrow setup over the other, I think you'd get lane imbalance issues. Or you'd get compliance issues in the second lane. A blank out sign to indicate the #2 lane signal is not in use during off-peak times would help inform the driver and deal with driver expectancy.

I think you'd have the same amount of obedience issues with blank-out signs and red arrows. Neither seems like a particularly good concept. Either way, it confuses drivers who expect both lanes to work the same (instead of having one lane closed sometimes, or having only one lane allowed to yield). I think you'd probably agree that having both lanes phased the same (pro or pro/per) would be far superior.

As far as lane balance, that's an issue IRL. Virginia never allows RTOR from the left lane of a double right turn. Everyone lines up in the lane that permits RTOR.

[jakeroot]

You guys probably think I've run out of things to post in this thread...wrong!

Kennewick, Washington recently activated two new double-left flashing yellow arrows. Both at the same intersection: Hildebrand Blvd @ Plaza Way, just northeast of the I-82/US-395 trumpet. One of the signals is for the SB to EB left turn (likely due to the short queue area), and the other is for the WB to SB left turn (implemented because Kennewick just likes this sort of thing; they've been using double permissive lefts since 2004).

https://goo.gl/GXbLQ4

[MNHighwayMan]

Found a protected-permissive dual left in Ankeny, Iowa for US 69/Ankeny Boulvard at 1st Street that uses two five-section towers:  Streetview

The Des Moines newspaper though indicates this will be changed to a single left.  http://www.desmoinesregister.com/story/news/local/ankeny/2017/09/29/ankeny-boulevard-and-1st-street-improvements-coming-2020/718133001/

Since jakeroot resurrected this thread from its two-month hibernation, here's a picture (which this thread inspired me to go get) of that dual-left setup in Ankeny that I took on Oct. 11. I would've posted a picture in the permissive phase, but apparently I didn't think to take one.

[Roadwarriors79]

In Chandler AZ, there are a few intersections with dual left turns where FYA signals have been installed. In Peoria AZ, I know of ONE intersection with dual left turns that uses FYA signals. The other intersections look like they were restriped to have a single left turn lane and new FYA installs. The other dual left turns are protected left signals.

[doorknob60]

ITD just posted this about the first dual permissive left just installed in Idaho: http://itd.idaho.gov/news/itd-tests-new-traffic-infrastructure-in-cda/

In an effort to improve mobility at a major intersection in Coeur d'Alene, ITD's North Idaho (District 1) traffic engineers activated a new signal function in December.

The signal at the Fourth Street on-ramp to Interstate 90 heading west now allows two lanes of traffic to turn left after yielding to oncoming vehicles and pedestrians. While local drivers may be familiar with how flashing yellow arrows function, this is the first site in the district–and the state–to use double flashing yellow arrows.

"This is one of the busiest intersections in the Coeur d'Alene metropolitan area, which is the fastest-growing area in the state,"  ITD District 1 Traffic Engineer Ben Ward said. "We're open to finding new ways to move more cars through."

The idea began with former traffic engineer Ryan Hawkins, who first saw a signal like this while passing through Kennewick, Washington, nearly three years ago.

"Technology like this can be leveraged to maintain mobility in congested corridors,"  Hawkins said. "We can't build our way out of this congestion, so we have to identify other options to optimize the infrastructure we currently have."

After his trip through Kennewick, Hawkins talked to signal manufacturers and brought the idea back to the department's working groups tasked with identifying innovative solutions. Access to westbound I-90 from Fourth Street became an informal test site for the rest of the state.

Ward said he was initially concerned the public would be confused when approaching this intersection, but since activating the new function three months ago, there have been no issues.

"We haven't received any concerned calls, and there haven't been any crashes out there because of the signal,"  Ward said. "The signal is moving traffic better."

Since there are not many signals like this in the region, Ward plans to monitor the site to determine if this technology should be implemented at other busy intersections, such as Prairie Avenue and ID-41 in an upcoming project.

"Right now, we are still watching the signal to make sure it is safe before we start installing more,"  Ward said. "So far, so good."

Side note, I never knew there was one in Kennewick. Used to live near there, but that was over a decade ago now :O

[US 89]

There are no dual permissive lefts, but there are many dual permissive right turns in Utah. If there's a right turn filter signal, it's almost always a doghouse.
Here's one in Lehi, UT with double doghouses, which I don't think I've seen anywhere else in UT.

[jakeroot]

ITD just posted this about the first dual permissive left just installed in Idaho: http://itd.idaho.gov/news/itd-tests-new-traffic-infrastructure-in-cda/

Nice! Freeway on ramps are the perfect place for these.

Side note, I never knew there was one in Kennewick. Used to live near there, but that was over a decade ago now :O

Kennewick has had a few in place since at least 2008. At the top of this page, I actually posted an image of a recent install in Kennewick. It appears as though its now the standard for double left turns.

[jakeroot]

Not sure how common these are in Chicago, but I found one near the north end of Lake Shore Drive involving an option lane:

https://goo.gl/vj8bsC

[US 89]

Not sure how common these are in Chicago, but I found one near the north end of Lake Shore Drive involving an option lane:

https://goo.gl/vj8bsC

If that were in Utah, it would almost certainly be split phased.

[jakeroot]

In South Africa, the "clearance" interval is typically two seconds. I think it may need to be a bit longer at this junction:

M17/M9 junction, Ottery, Cape Town

By my own estimations, the bottom-to-right storage box can accommodate about 12 cars at a time. Judging by street view (elsewhere, as this junction was just opened), South Africans lodge themselves as far forward as they possibly can (past the stop line) when waiting to turn right, so it's not unlikely that 12 would actually be out there waiting to turn. At this slightly more normal double permissive right, there's eight cars waiting past the stop line.

[jakeroot]

Not sure how common these are in Chicago, but I found one near the north end of Lake Shore Drive involving an option lane:

https://goo.gl/vj8bsC

If that were in Utah, it would almost certainly be split phased.

As I think it normally would be in Illinois and most other areas (except a few cities such as Tucson or areas around Denver). Seattle has a double permissive left turn with an option lane just like this image (except with one more through lane), which I posted an image of on the first page (the OP, actually).

[MCRoads]

Found one!!!

Academy and Carefree in Colorado Springs!!!