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What's Your Favorite Controlled Left Turn (and Why)?

Started by Ned Weasel, April 08, 2021, 10:29:05 AM

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What is your favorite type of controlled left turn?

Protected/Permissive (Includes FYA)
Protected-Only
Forward Jughandle
Reverse Jughandle (Loop after Intersection)
Michigan Left or Downstream U-Turn
RCUT
Roundabout
Hamburger Junction
No Left Turn--Find Your Own Way!
Other (Please Explain)

Scott5114

Quote from: stridentweasel on April 21, 2021, 06:56:33 AM
Oklahoma seems to be one place with a lot of protected-only left turns in places that at least appear as if protected/permissive would be feasible.  Just look at US 69 in Muskogee, for example.  FWIW, the city I live in has been moving to protected/permissive about everywhere it can, but stopping short of going full-Tucson with protected/permissive double left turns.

It very much depends on the city. Damn near every intersection in Norman that isn't a double left is protected/permissive, including some where it's probably not very helpful due to the volume of oncoming traffic.
uncontrollable freak sardine salad chef


Ned Weasel

^ I would think this is something where the State DOT should step in when it's a State or US highway.
"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.

mrsman

Quote from: JoePCool14 on April 22, 2021, 10:03:47 AM
Quote from: mrsman on April 11, 2021, 11:54:28 AM
Quote from: kphoger on April 09, 2021, 12:00:56 PM
Quote from: Revive 755 on April 08, 2021, 10:20:28 PM

Quote from: kphoger on April 08, 2021, 12:47:17 PM
Didn't North Avenue (IL-64) use to have a section or two like this?  I can't seem to find it on GSV right now, but maybe they got rid of that.

* North Avenue at Roy Avenue

* North Avenue at Cornell Avenue/35th Avenue

* North Avenue at Hawthorne Avenue



Also a couple sections on Palatine Road but with one way frontage roads.

* Palatine Road at Windsor Drive

* Palatine Road at Schoenbeck Road

* Palatine Road at Wheeling Road

Thank you.  The Palatine Road examples are what I was looking for, but it appears left turns at all of your North Avenue examples are now handled in the typical way from the main lanes:  left-turn lane, five-section signal.

I am looking through these pictures of Palatine Rd. and I'm not understanding the benefit of allowing left turns from the service road.  Left turns in the service road would require a separate signal phase from thru traffic, thus adding phases to the signal and slowing everyone down.  It would seem easier to use some of the ROW of the service road to make the main road wide enough for left turn lanes. 

Here is another example of left turn from a service road, but it is limited to buses.  The westbound Q46 bus comes from Union Turnpike, makes a right onto the Queens Blvd service road and discharges all its passengers at the first stop.  (This stop is right next to the subway entrance.)  It then picks up a new set of eastbound passengers at the same stop and drives along the service road to this traffic signal.  When main lanes get a protected left, buses also get a left to make a u-turn to head back to Union Turnpike.

https://www.google.com/maps/@40.7160848,-73.833132,3a,37.5y,307.47h,85.92t/data=!3m6!1e1!3m4!1s2UBDSRDeVr3x4kIHUnNHLg!2e0!7i16384!8i8192

I'm not personally a fan of Palatine Rd exactly for the reason you stated, and I live about ten minutes away from it, so I'm pretty familiar with the road. The light takes a long time to cycle through, with phases for the Palatine Rd thru-traffic, the side streets which now all have protected-permissive left signals also, and two separate phases for the frontage roads, one for each direction. There's been times where I've hit all three of these lights wrong while on Palatine and it's not fun waiting.

In an ideal world I'd like to see IDOT convert these three intersections to something similar to what's at IL-83 / Elmhurst Rd. Then you'd only have to deal with traffic at Rand Rd, Arlington Heights Rd, and Kennicott Dr.

Sure, a full fledged grade separation is wonderful, but so expensive that only a limited number of surface intersections can be converted as such.

roadfro

Quote from: stridentweasel on April 21, 2021, 06:56:33 AM
<SNIP> And why do so many places still use protected-only left turns when, absent of a rigorous study on my part, it at least looks like protected/permissive would be feasible?

Oklahoma seems to be one place with a lot of protected-only left turns in places that at least appear as if protected/permissive would be feasible.  Just look at US 69 in Muskogee, for example.  FWIW, the city I live in has been moving to protected/permissive about everywhere it can, but stopping short of going full-Tucson with protected/permissive double left turns.

I think this has to do, in part, with the signal philosophy of the local public works department. Some agencies have very rigid criteria as to when they will consider PPLT phasing as opposed to protected-only, whereas other agencies may be more lax.

It also likely has to do with cost. There just may not be funds available to convert protected-only to PPLT when there's other competing needs vying for limited dollars, especially for smaller jurisdictions. To make this conversion, you have to purchase and install the new signal heads as well as potentially pull new wiring. If the existing signal controller doesn't have PPLT logic or doesn't have the FYA logic (which may be likely if the controller was installed before the mid-2000's), you may need to go through a bigger monetary investment of replacing the controller to implement PPLT phasing. For some agencies, the cost may not be worth it.

Quote from: stridentweasel on April 23, 2021, 07:02:30 AM
^ I would think this is something where the State DOT should step in when it's a State or US highway.

Depends on how things are set up. For example, in Nevada, NDOT may maintain the state highway, but they actually don't maintain the signals they install on said highways–signal operation is generally left to the local city or county jurisdiction. The state may not get a say unless they're going to provide funding to the local agency for any signal upgrades, or some other agreement is brokered.
Roadfro - AARoads Pacific Southwest moderator since 2010, Nevada roadgeek since 1983.

US 89

Quote from: MCRoads on April 22, 2021, 12:10:35 PM
Maybe this is a niche, but I really like double left permissive left turns. There is one near me with 2 doghouse signals (my favorite type of signal), so that is my favorite intersection.

Personal opinion: double doghouses look gross.

Scott5114

Quote from: stridentweasel on April 23, 2021, 07:02:30 AM
^ I would think this is something where the State DOT should step in when it's a State or US highway.

I'm of two minds on this. Having the state DOT assert jurisdiction over state highways means that signal policy is uniform statewide on state highways, which is good, especially on lengths of rural highway where one is passing through several small cities with stoplights where the state highway intersects the main drag.

However, it means that large cities that have state highways passing through them will have corridors where the signals will be consistent with each other, but not with the rest of the city. I'm thinking about MoDOT specifically here, which makes no attempt at making its signals and signal signage resemble nearby city installs in style or operation. This particularly sticks out in cities like Springfield which are criss-crossed by a lot of state highways.

In Oklahoma specifically, I'm kind of glad that ODOT doesn't enforce policy on city-maintained signals, because their signal installations leave a lot to be desired. Many of their installations in McClain County still use incandescent bulbs, and I can think of one that has extremely laggy actuation equipment, so you are left to sit at a red light waiting to turn for a kind of absurd amount of time at 12am.
uncontrollable freak sardine salad chef

Ned Weasel

Quote from: roadfro on April 24, 2021, 01:51:37 PM
There just may not be funds available to convert protected-only to PPLT when there's other competing needs vying for limited dollars, especially for smaller jurisdictions.

Was protected-only invented before PPLT?  Or was protected-only just really over-used for a long period of time, and if so, do you know what drove that philosophy?  Was it simply a matter of being overly cautious?  I can see that, except it seems inconsistent with allowing unprotected left turns at most non-signalized intersections, which tends to happen in most states that are not New Jersey.
"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.

roadfro

Quote from: stridentweasel on April 24, 2021, 10:40:12 PM
Quote from: roadfro on April 24, 2021, 01:51:37 PM
There just may not be funds available to convert protected-only to PPLT when there's other competing needs vying for limited dollars, especially for smaller jurisdictions.

Was protected-only invented before PPLT?  Or was protected-only just really over-used for a long period of time, and if so, do you know what drove that philosophy?  Was it simply a matter of being overly cautious?  I can see that, except it seems inconsistent with allowing unprotected left turns at most non-signalized intersections, which tends to happen in most states that are not New Jersey.

I can't speak with certainty without doing additional research, but it seems reasonable to conclude that protected-only phasing has been around far longer than PPLT phasing (at least through phasing types that use doghouses or FYA displays now in the MUTCD). My hunch is that protected-only phasing was developed as a safety measure (beyond permitted-only) for busy intersections or possibly a capacity measure, and then PPLT displays were later adopted to help reduce delay during non-peak periods.

Protected-only still seems to be overused by some jurisdictions...possibly because of old policy or safety rationales held by the agency ("a permitted left turn across two lanes is unsafe", "a permissive turn when opposing speed limit is 40 or greater causes increased crashes", etc. [neither of which I 100% agree with]), possibly because the agency has not sought to make any changes (operating under the "if it ain't broke..." philosophy or otherwise), or possibly because nobody has ever brought up the idea of using PPLT's.
Roadfro - AARoads Pacific Southwest moderator since 2010, Nevada roadgeek since 1983.

jakeroot

Quote from: roadfro on April 24, 2021, 01:51:37 PM
It also likely has to do with cost. There just may not be funds available to convert protected-only to PPLT when there's other competing needs vying for limited dollars, especially for smaller jurisdictions. To make this conversion, you have to purchase and install the new signal heads as well as potentially pull new wiring. If the existing signal controller doesn't have PPLT logic or doesn't have the FYA logic (which may be likely if the controller was installed before the mid-2000's), you may need to go through a bigger monetary investment of replacing the controller to implement PPLT phasing. For some agencies, the cost may not be worth it.

I would be curious if the logic on older controllers would permit changing the left turns from protected-only to permissive-only (by removing the left turn signals).

Good example is this intersection in Tacoma. Neither street possesses anywhere near the traffic levels required for a protected-only left turn, much less a PPLT. Assuming the controller logic isn't capable of PPLT (either "yield on green" or FYA), it would be easier to simply rip out the protected lefts altogether.

roadfro

Quote from: jakeroot on April 25, 2021, 03:23:05 PM
Quote from: roadfro on April 24, 2021, 01:51:37 PM
It also likely has to do with cost. There just may not be funds available to convert protected-only to PPLT when there's other competing needs vying for limited dollars, especially for smaller jurisdictions. To make this conversion, you have to purchase and install the new signal heads as well as potentially pull new wiring. If the existing signal controller doesn't have PPLT logic or doesn't have the FYA logic (which may be likely if the controller was installed before the mid-2000's), you may need to go through a bigger monetary investment of replacing the controller to implement PPLT phasing. For some agencies, the cost may not be worth it.

I would be curious if the logic on older controllers would permit changing the left turns from protected-only to permissive-only (by removing the left turn signals).

Good example is this intersection in Tacoma. Neither street possesses anywhere near the traffic levels required for a protected-only left turn, much less a PPLT. Assuming the controller logic isn't capable of PPLT (either "yield on green" or FYA), it would be easier to simply rip out the protected lefts altogether.
Removing a protected-only phase and having no separate left turn phases shouldn't be a problem for most signal controllers.

The initial transition from doghouses to FYAs may have been a challenge in some cases, because older signal controllers didn't have the programming to run the FYA logic and I believe in some cases couldn't be reprogrammed to do so. (Similarly, many places running Dallas Phasing prior to the proliferation of FYA needed special controller logic to run it, because some of the principles conflict with standard NEMA signal controller programming.)
Roadfro - AARoads Pacific Southwest moderator since 2010, Nevada roadgeek since 1983.



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