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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

jakeroot

I have brought this topic up so many times in the past, I must appear to be obsessed with these things now. I certainly don't want it to look like that, but dual permissive left turns have to be one of the rarest forms of traffic control in the business, far, far less common than even the modern roundabout. I'm fairly certain that they're limited to North America and maybe China.

I remember seeing my first double permissive left in Colorado Springs when I was maybe 11 or 12. The exit from my grandparent's neighborhood leads to a signal at Chestnut St and Garden of the Gods Road, which is a permissive double left. I always thought this was strange, simply because I had never seen this before in Washington or BC, and also because so many single lane turns in my area are protected-only, it boggled my mind how there could be two lanes that could yield. Anyways, years later, on a trip through Edmonton, Alberta, I encountered a slew of these double permissive turns. Once again, I was mesmerized by them. The capacity of the turn seems to explode when there's two lanes yielding. Very rarely sat and waited to turn up there. I have been impressed (read: obsessed) ever since.

So, the purpose of this thread? I'd like to know your thoughts on these things. Do you think they're a bad idea? Do you wish they were used more? You're welcome to list where these things are located if you know of any (I've asked on other threads already, but for continuity, it might be better to "relist" them here). No need to point out Tucson, AZ or Richardson/McKinney, TX, as they're already quite well known for theirs.

Quite a few state DOT's do not permit their use (WSDOT's MUTCD states, very plainly, that permissive lefts are not allowed "on intersection approaches that have dual left-turn lanes"). But, on roads not maintained by the state, these things are fair game. Locally, Seattle has a couple that I know of, Kennewick (WA) has at least two or three, and Silverdale (WA) used to have one before it was removed. Federal Way (WA) intends to install one in the future, but nothing official has come around (short of a short snippet (see p. 25) from the chief engineer a few months ago)

I've run over the inherent ups and downs over the years:

+ increased capacity
+ more green time for through traffic
+ speeds up travel times? (I suppose these three are all connected in some way)
+ higher level of functionality (protected only some times, permissive only others) with FYAs

- potentially increased danger because there's simply a higher chance of something going wrong
- driver's may not understand the flashing yellow arrow?
- potentially reduced visibility for inside lane's car, depending on where the outside lane's car is waiting

Here's an image of a typical FYA setup (James St at 6th Ave, Seattle):



Ace10

#1
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)). Popps Ferry/Cedar Lake's dual permissive lefts are only for eastbound Popps Ferry traffic turning left onto northbound Cedar Lake, but MS 605/Pass Rd's dual permissive lefts are for E/W Pass Rd traffic turning left onto N/S MS 605.

#3 (Rodriguez & SB I-110) is unique in that there are dual permissive lefts, but the outside (rightmost) left turn lane is also a through lane. The rightmost lane is the only dedicated through lane. #1 (Cedar Lake & Popps Ferry) used to have this setup when I first began driving but it's been changed so that both left turn lanes are dedicated and the right lane is optional through/right turn.

For the second intersection (MS 605 & Pass Rd), I don't know why all four directions don't have dual permissive lefts. It's very flat and straight at that intersection. If one road can have it, why not both? Especially the one with less through traffic? Also interestingly there is only one doghouse per direction on Pass Rd, but two left turn lanes. I have a feeling this intersection was widened a while back and maybe the old signals were kept.

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.

I like them, particularly if there is a high volume of left-turning traffic and perhaps not as much through traffic. There are a few intersections west of Portland - one namely is Baseline Rd and Cornelius Pass Rd, where traffic turning left from E/W Baseline onto N/S Cornelius Pass face a double protected-only arrow. I've been at that intersection enough times where through traffic on Baseline is clear and other traffic could easily turn left, but they're stuck at the red arrow.

The only con I can say I've experienced was the reduced visibility if you're in the inside (left-most) left turn lane. If I'm behind a long line of cars that have just begun turning on the permissive movement, unless I have clear shot of (lack of) opposing traffic, I'll lag a little behind until I'm sure the way is clear before I turn. If there's another lane to the right of me making the same turn, I'd either have to potentially wait longer for visual clearance or trust the person to the right of me to also yield, else an accident would ensue.

roadman65

Florida did have it in Kissimmee, FL on John Young Parkway and Carroll Street.  It lasted for a few months before Kissimmee (in Florida the state does not at all maintain or operate signals) realized that it was two lanes turning left with one doghouse for both lanes.  So in essence they added two left turn signals and made the turn on green arrow only.

This all happened when JYP was made to connect Kissimmee with Hunters Creek back in the early 90's. 
Every day is a winding road, you just got to get used to it.

Sheryl Crowe

cl94

I'm not a big fan of them. With permissive movements especially, cars don't always follow a nice, curved path while turning due to other factors. Have 2 cars trying to make the turn and I see the risk for sideswiping.
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)

froggie

Ace10 beat me to the Mississippi Coast examples.

MnDOT policy on dual left turn lanes is that they must be protected-only.

freebrickproductions

Several around here in Huntsville, AL. I'll post them in a little bit.
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)

JCinSummerfield

I think if you're going to have them, you should at least have FYA for permissive left turns.

briantroutman

As much as I hate to cater to the lowest common denominator of uneducated driver, I think dual permissive left turns (particularly with a flashing left arrow) may be a bridge too far.

There are just too many minuses:

- too many drivers already lack lane discipline even in protected multi-lane turns
- difficulty in making a judgement due to alternating vehicular and pedestrian traffic–or worse, reckless disregard for pedestrians, oncoming vehicles, or both
- general unfamiliarity with flashing yellow arrow
etc.

Any one of these issues already exist in other situations, but I think having all of these (and more) combined in one situation tilts the scales toward the arrangement being not recommendable, in my opinion.

cl94

Quote from: briantroutman on December 14, 2015, 01:38:51 PM
- too many drivers already lack lane discipline even in protected multi-lane turns

Yeah. I get cut off at least once a week at a double protected left/right because people either turn into the other lane or cross the dividing line while making the turn. People don't understand how to be safe in protected left turns. Why add more dangerous elements?
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

Quote from: cl94 on December 14, 2015, 01:55:53 PM
Quote from: briantroutman on December 14, 2015, 01:38:51 PM
- too many drivers already lack lane discipline even in protected multi-lane turns

Yeah. I get cut off at least once a week at a double protected left/right because people either turn into the other lane or cross the dividing line while making the turn. People don't understand how to be safe in protected left turns. Why add more dangerous elements?

That might be a regional thing. Like basically any traffic control device, there are parts of the country where it works better than others. There are more than a few double left turns near me, and I really can't recall being cut off before. As long as the lane lines are delineated well throughout the intersection, I don't think it's as big of a problem as it may appear to be.

busman_49

The only one I can think off that I've seen is in Stow, Ohio.  The first time I saw it, it was a WTF moment for me, only because I didn't realize that sort of thing existed.
https://www.google.com/maps/@41.1666559,-81.4406866,3a,75y,94.34h,72.57t/data=!3m6!1e1!3m4!1sJNPccP0xB1x38IEhpUKcPw!2e0!7i13312!8i6656!6m1!1e1

riiga

It's certainly a very intriguing concept, but they both violate the Vienna Convention and most probably lead to more accidents than a regular protected turn signal for a very negligable capacity improvement. As such I imagine none will ever be built here or in the rest of Europe.

UCFKnights

I've only seen 1 or 2 in my life but I really liked them, especially now with FYAs. It seems lilke an easy way to add quite a bit of traffic flow improvements. I see everyone here is claiming way too dangerous... I'd like to see some data on this. anyone have that available?

cl94

Quote from: UCFKnights on December 14, 2015, 05:52:09 PM
I've only seen 1 or 2 in my life but I really liked them, especially now with FYAs. It seems lilke an easy way to add quite a bit of traffic flow improvements. I see everyone here is claiming way too dangerous... I'd like to see some data on this. anyone have that available?

I'm going by how people drive on dual left turns in the midwest. I've seen too many accidents happen due to people leaving their lane while turning.
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)

tradephoric

Studies have found that a significant percentage of drivers don't look to see if there are pedestrians in the crosswalk when making a permissive left (drivers are focused on gaps in opposing traffic).  At a single permissive left-turn, drivers have the opportunity to swerve around a pedestrian they didn't initially see.  At a dual permissive left-turn, drivers may not be able to swerve since a vehicle would very likely be next to them (or they do swerve to avoid the pedestrian and sideswipe the vehicle next to them... potentially causing that vehicle to lose control and run into the sidewalk).  It just sounds like a bad scenario.   

1995hoo

I can't say I ever recall seeing dual permissive left turns (doesn't mean I haven't seen one, just that I do not ever remember it). Given that VDOT is religious about prohibiting right turns on red from any lane other than the curb lane, I highly doubt they'd ever allow dual permissive lefts.

The thing this thread makes me think of is the thread a few months ago about whether it's OK, or a good idea, to pull out into the intersection while waiting to make a permissive left turn. In places where that practice is routine, I could see permissive dual lefts being a problem because of visibility issues. It can be hard enough to see to go left when there's one large truck or SUV pulled out waiting to turn opposite you. If there were two such vehicles, it would likely be considerably more difficult for the driver in the right-hand lane of the two left-turn lanes to see oncoming traffic, unless you had some sort of median or other way of staggering the turn lanes away from the thru lanes (which is uncommon in Virginia, at least).
"You know, you never have a guaranteed spot until you have a spot guaranteed."
—Olaf Kolzig, as quoted in the Washington Times on March 28, 2003,
commenting on the Capitals clinching a playoff spot.

"That sounded stupid, didn't it?"
—Kolzig, to the same reporter a few seconds later.

UCFKnights

Quote from: 1995hoo on December 14, 2015, 07:29:49 PM
I can't say I ever recall seeing dual permissive left turns (doesn't mean I haven't seen one, just that I do not ever remember it). Given that VDOT is religious about prohibiting right turns on red from any lane other than the curb lane, I highly doubt they'd ever allow dual permissive lefts.

The thing this thread makes me think of is the thread a few months ago about whether it's OK, or a good idea, to pull out into the intersection while waiting to make a permissive left turn. In places where that practice is routine, I could see permissive dual lefts being a problem because of visibility issues. It can be hard enough to see to go left when there's one large truck or SUV pulled out waiting to turn opposite you. If there were two such vehicles, it would likely be considerably more difficult for the driver in the right-hand lane of the two left-turn lanes to see oncoming traffic, unless you had some sort of median or other way of staggering the turn lanes away from the thru lanes (which is uncommon in Virginia, at least).
I'm curious if there exists a permissive turn left lane only? That would solve a lot of the complaints mentioned here, and I know around here, there are a number of right turn on red right lane only and they seem to operate without issue. Well, we have a few right turn on red from 2 right turn lanes and they also operate seemingly fine and help deal with traffic congestion.

jakeroot

Quote from: UCFKnights on December 14, 2015, 08:09:20 PM
Quote from: 1995hoo on December 14, 2015, 07:29:49 PM
I can't say I ever recall seeing dual permissive left turns (doesn't mean I haven't seen one, just that I do not ever remember it). Given that VDOT is religious about prohibiting right turns on red from any lane other than the curb lane, I highly doubt they'd ever allow dual permissive lefts.

The thing this thread makes me think of is the thread a few months ago about whether it's OK, or a good idea, to pull out into the intersection while waiting to make a permissive left turn. In places where that practice is routine, I could see permissive dual lefts being a problem because of visibility issues. It can be hard enough to see to go left when there's one large truck or SUV pulled out waiting to turn opposite you. If there were two such vehicles, it would likely be considerably more difficult for the driver in the right-hand lane of the two left-turn lanes to see oncoming traffic, unless you had some sort of median or other way of staggering the turn lanes away from the thru lanes (which is uncommon in Virginia, at least).

I'm curious if there exists a permissive turn left lane only?

But wouldn't everyone just stay in the lane that permits turns? You'd have a pretty uneven lane balance I'd think.

Quote from: tradephoric on December 14, 2015, 06:48:40 PM
Studies have found that a significant percentage of drivers don't look to see if there are pedestrians in the crosswalk when making a permissive left (drivers are focused on gaps in opposing traffic).  At a single permissive left-turn, drivers have the opportunity to swerve around a pedestrian they didn't initially see.  At a dual permissive left-turn, drivers may not be able to swerve since a vehicle would very likely be next to them (or they do swerve to avoid the pedestrian and sideswipe the vehicle next to them... potentially causing that vehicle to lose control and run into the sidewalk).  It just sounds like a bad scenario.   

A pretty common scenario with permissive turns, number of lanes irrelevant, is having the FYA go red when the pedestrian walk signal is green (Bellevue, WA does this at many of their FYAs). This might solve that problem.

1995hoo

Quote from: jakeroot on December 14, 2015, 09:51:20 PM
Quote from: UCFKnights on December 14, 2015, 08:09:20 PM
Quote from: 1995hoo on December 14, 2015, 07:29:49 PM
I can't say I ever recall seeing dual permissive left turns (doesn't mean I haven't seen one, just that I do not ever remember it). Given that VDOT is religious about prohibiting right turns on red from any lane other than the curb lane, I highly doubt they'd ever allow dual permissive lefts.

The thing this thread makes me think of is the thread a few months ago about whether it's OK, or a good idea, to pull out into the intersection while waiting to make a permissive left turn. In places where that practice is routine, I could see permissive dual lefts being a problem because of visibility issues. It can be hard enough to see to go left when there's one large truck or SUV pulled out waiting to turn opposite you. If there were two such vehicles, it would likely be considerably more difficult for the driver in the right-hand lane of the two left-turn lanes to see oncoming traffic, unless you had some sort of median or other way of staggering the turn lanes away from the thru lanes (which is uncommon in Virginia, at least).

I'm curious if there exists a permissive turn left lane only?

But wouldn't everyone just stay in the lane that permits turns? You'd have a pretty uneven lane balance I'd think.

....

That's what happens here with dual right turns. Everyone who lives around here knows that more than 99% of the time there'll be a sign prohibiting right on red from anywhere but the far right lane, so almost everyone will use only the far right lane unless the light is already green.

(I say "more than 99% of the time" because I can readily think of one light that doesn't have this restriction posted–the dual right turn from westbound Huntington Avenue to northbound Telegraph Road just south of the Beltway. Also, oddly, where there are dual left-turn lanes and a left-on-red situation, I've never seen a sign restricting lefts on red to the far left lane, although I have seen a "No Turn on Red" sign at a left-on-red spot.)
"You know, you never have a guaranteed spot until you have a spot guaranteed."
—Olaf Kolzig, as quoted in the Washington Times on March 28, 2003,
commenting on the Capitals clinching a playoff spot.

"That sounded stupid, didn't it?"
—Kolzig, to the same reporter a few seconds later.

UCFKnights

Quote from: jakeroot on December 14, 2015, 09:51:20 PM
Quote from: UCFKnights on December 14, 2015, 08:09:20 PM
Quote from: 1995hoo on December 14, 2015, 07:29:49 PM
I can't say I ever recall seeing dual permissive left turns (doesn't mean I haven't seen one, just that I do not ever remember it). Given that VDOT is religious about prohibiting right turns on red from any lane other than the curb lane, I highly doubt they'd ever allow dual permissive lefts.

The thing this thread makes me think of is the thread a few months ago about whether it's OK, or a good idea, to pull out into the intersection while waiting to make a permissive left turn. In places where that practice is routine, I could see permissive dual lefts being a problem because of visibility issues. It can be hard enough to see to go left when there's one large truck or SUV pulled out waiting to turn opposite you. If there were two such vehicles, it would likely be considerably more difficult for the driver in the right-hand lane of the two left-turn lanes to see oncoming traffic, unless you had some sort of median or other way of staggering the turn lanes away from the thru lanes (which is uncommon in Virginia, at least).

I'm curious if there exists a permissive turn left lane only?

But wouldn't everyone just stay in the lane that permits turns? You'd have a pretty uneven lane balance I'd think.
While I'm sure the lane balance would no longer be even, in the dual right turn lanes around here, people will still use the left of them when the right one is congested and its clear they will not get to go before the light changes anyways. You do want the lanes to not be exactly balanced as the capacity isn't quite equal o the lanes. In this case, it'd likely end up more balanced then the right lane scenario as after the light turns red, people will try to balance out the other lane during the entire red phase.

tradephoric

Quote from: jakeroot on December 14, 2015, 09:51:20 PM
A pretty common scenario with permissive turns, number of lanes irrelevant, is having the FYA go red when the pedestrian walk signal is green (Bellevue, WA does this at many of their FYAs). This might solve that problem.

The low compliance rate among pedestrians can make this type of setup more harmful then helpful.  It's conditioning drivers not to look for pedestrians during the permissive phase even though pedestrians may very well be present (since a pedestrian may simply chose not to push the pushbutton).  There is a 2001 study from Windsor, Ontario where the pushbutton was actuated in only 32% of the cycles where a pedestrian crossed the street.

roadfro

Quote from: jakeroot on December 14, 2015, 09:51:20 PM
A pretty common scenario with permissive turns, number of lanes irrelevant, is having the FYA go red when the pedestrian walk signal is green (Bellevue, WA does this at many of their FYAs). This might solve that problem.

I don't think I've ever seen this... It also seems that the capacity of the PPLT would be reduced considerably in such a case where this is done.
Roadfro - AARoads Pacific Southwest moderator since 2010, Nevada roadgeek since 1983.

jakeroot

#22
Quote from: roadfro on December 15, 2015, 01:01:40 AM
Quote from: jakeroot on December 14, 2015, 09:51:20 PM
A pretty common scenario with permissive turns, number of lanes irrelevant, is having the FYA go red when the pedestrian walk signal is green (Bellevue, WA does this at many of their FYAs). This might solve that problem.

I don't think I've ever seen this... It also seems that the capacity of the PPLT would be reduced considerably in such a case where this is done.

Sorry, should have been more specific. I have witnessed this in Bellevue, WA.

One of Bellevue's engineers, Mark Poch, gave a presentation a few years ago, and there's a snippet from that powerpoint, which I have seen many times implemented in Bellevue, which suggests eliminating the permissive phase during walk signals:

Quote
How? SCATS "Ped Minus Left"  Feature

- Omit permissive portion of pro/per when the crosswalk has a walk or flashing don't walk indication

Here's the whole presentation: http://goo.gl/sqg5qV. Page 19 has that quote on it, followed by a bunch of examples.

Quote from: UCFKnights on December 14, 2015, 05:52:09 PM
I've only seen 1 or 2 in my life but I really liked them, especially now with FYAs. It seems lilke an easy way to add quite a bit of traffic flow improvements. I see everyone here is claiming way too dangerous... I'd like to see some data on this. anyone have that available?

Exact data? Not really much. But the Virginia DOT (I cited this earlier) collected statements from different agencies about their experiences with flashing yellow arrows, and some of them noted their uses with double permissive lefts:

Kennewick, Washington:

QuoteIt is not necessarily true that two lanes require Protected Only phasing. We run two locations like that. Our first location was turned on December 20th, 2004. It now serves a Home Depot, Walgreen's, Starbuck's, Pet Smart, and a few other small shops while the other side is single turn lane and serves Wal‐Mart, Burger King, Best Western, McDonalds and a gas station. This setup works fine because the two lanes both have clear vision of oncoming traffic, the opposing traffic is random arrival, and has adequate gaps. The two‐lanes were needed for storage due to [its] close proximity to a US Highway. Both turn lanes get used regularly and simultaneous traffic turning from the two lanes is not uncommon. I checked statistics and the actual left turn on the dual lane side gets triggered 20% of cycles or less. The Wal‐mart side gets triggered about 50% of the time through the peak hours.

Boulder, Colorado:

QuoteActually we've had good success with using Protected/Permissive phasing (by time of day) on dual left‐turn lane approaches.  We are certainly not the only community in Colorado to do this either.  I've yet to see any data that supports the premise  that multiple left‐turn lanes requires protected only phasing.  I've always considered that to be "Folklore".

Richardson, Texas (by way of Las Vegas):

QuoteAllow me to add credence to it being "Folklore" that dual lefts require protected only.  When I was starting my municipal traffic engineering career in Richardson (TX) in the early 1980's, dual left‐turn lanes were the BIG NEW THING.  We went ahead and built signals at all of our major‐crossing‐major intersections having dual left turns with 5‐section left‐turn heads, and they almost all ran PPLT 24x7x365. The drivers became accustomed to it, and didn't crash (at a too‐high rate). You can Google Street View just about any major arterial intersection in Richardson today, and you'll see this practice survives 30 years on.

The quotes start on page 64 according to the PDF, though the page number on the bottom is 25.

Tom958

Quote from: roadman65 on December 14, 2015, 03:25:32 AM
Florida did have it in Kissimmee, FL on John Young Parkway and Carroll Street.  It lasted for a few months before Kissimmee (in Florida the state does not at all maintain or operate signals) realized that it was two lanes turning left with one doghouse for both lanes.  So in essence they added two left turn signals and made the turn on green arrow only.

There's one near my house in Gwinnett County, GA. It's an anomaly, AFAIK, but it's been like this for decades, even as FYA's have started to appear nearby. I hope it remains as is-- I've never had a problem with it. I guess that's mainly because straight-through traffic between Cruse Road and Marathon Blvd is very light.

UCFKnights

Quote from: jakeroot on December 15, 2015, 02:06:06 AM
Quote from: roadfro on December 15, 2015, 01:01:40 AM
Quote from: jakeroot on December 14, 2015, 09:51:20 PM
A pretty common scenario with permissive turns, number of lanes irrelevant, is having the FYA go red when the pedestrian walk signal is green (Bellevue, WA does this at many of their FYAs). This might solve that problem.

I don't think I've ever seen this... It also seems that the capacity of the PPLT would be reduced considerably in such a case where this is done.

Sorry, should have been more specific. I have witnessed this in Bellevue, WA.

One of Bellevue's engineers, Mark Poch, gave a presentation a few years ago, and there's a snippet from that powerpoint, which I have seen many times implemented in Bellevue, which suggests eliminating the permissive phase during walk signals:

Quote
How? SCATS "Ped Minus Left"  Feature

- Omit permissive portion of pro/per when the crosswalk has a walk or flashing don't walk indication

Here's the whole presentation: http://goo.gl/sqg5qV. Page 19 has that quote on it, followed by a bunch of examples.

Quote from: UCFKnights on December 14, 2015, 05:52:09 PM
I've only seen 1 or 2 in my life but I really liked them, especially now with FYAs. It seems lilke an easy way to add quite a bit of traffic flow improvements. I see everyone here is claiming way too dangerous... I'd like to see some data on this. anyone have that available?

Exact data? Not really much. But the Virginia DOT (I cited this earlier) collected statements from different agencies about their experiences with flashing yellow arrows, and some of them noted their uses with double permissive lefts:

Kennewick, Washington:

QuoteIt is not necessarily true that two lanes require Protected Only phasing. We run two locations like that. Our first location was turned on December 20th, 2004. It now serves a Home Depot, Walgreen's, Starbuck's, Pet Smart, and a few other small shops while the other side is single turn lane and serves Wal‐Mart, Burger King, Best Western, McDonalds and a gas station. This setup works fine because the two lanes both have clear vision of oncoming traffic, the opposing traffic is random arrival, and has adequate gaps. The two‐lanes were needed for storage due to [its] close proximity to a US Highway. Both turn lanes get used regularly and simultaneous traffic turning from the two lanes is not uncommon. I checked statistics and the actual left turn on the dual lane side gets triggered 20% of cycles or less. The Wal‐mart side gets triggered about 50% of the time through the peak hours.

Boulder, Colorado:

QuoteActually we've had good success with using Protected/Permissive phasing (by time of day) on dual left‐turn lane approaches.  We are certainly not the only community in Colorado to do this either.  I've yet to see any data that supports the premise  that multiple left‐turn lanes requires protected only phasing.  I've always considered that to be "Folklore".

Richardson, Texas (by way of Las Vegas):

QuoteAllow me to add credence to it being "Folklore" that dual lefts require protected only.  When I was starting my municipal traffic engineering career in Richardson (TX) in the early 1980's, dual left‐turn lanes were the BIG NEW THING.  We went ahead and built signals at all of our major‐crossing‐major intersections having dual left turns with 5‐section left‐turn heads, and they almost all ran PPLT 24x7x365. The drivers became accustomed to it, and didn't crash (at a too‐high rate). You can Google Street View just about any major arterial intersection in Richardson today, and you'll see this practice survives 30 years on.

The quotes start on page 64 according to the PDF, though the page number on the bottom is 25.
Interesting.... another one I thought was pretty interesting and would like to see play out:
Quote
For single left‐turn lanes, I rarely find that the signal needs protection 24/7/365.   Herein lies one of the
wonderful applications of the FYA.   It affords the ability to run the needed indication according to the
conditions.    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 would stay red
and the blankout sign would flash if the detector for that lane became active.
Point here, as technology changes we should seriously examine the past paradigms to see whether
application of this technology can provide better service to our customers without sacrificing safety. By
displaying the correct design for the conditions, we are also most likely to gain the best compliance from
our roadway users and generate respect for the work we do.   Let's also remember that most signals
are designed to handle the peak hour load which by logic of the K factor represents only 20% of our
users.   What about the other 80%?



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