Double left turns with permissive phasing

[jakeroot]

I added a poll. A bit late, but it doesn't hurt.

[Super Mateo]

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.

In the south suburbs of Chicago, the dotted line indicating where to turn is usually ignored.  The drivers in the outer lane frequently tend to cross it, varying from just half a tire width to the entire car being inside the curve.  They often don't allow the inner lane enough room and it often leads to the inner cars either hitting the median or causing the end of the turn to be extra sharp.  I will not use the left/inner lane of a double left anymore because it has become that bad.

[MASTERNC]

I remember seeing one in Michigan (at least I think it was) about 12 years ago.  It wasn't until April that I saw another one, this one in Castle Rock, CO.

[cl94]

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.

In the south suburbs of Chicago, the dotted line indicating where to turn is usually ignored.  The drivers in the outer lane frequently tend to cross it, varying from just half a tire width to the entire car being inside the curve.  They often don't allow the inner lane enough room and it often leads to the inner cars either hitting the median or causing the end of the turn to be extra sharp.  I will not use the left/inner lane of a double left anymore because it has become that bad.

It extends east to at least Buffalo (which may as well be considered the Midwest). I see that every day. That or people on the inside take it too wide. Quite often, you'll have people on the inside making their turn so they end on the outside.

[1995hoo]

Around here it's the people in the inside lane taking a wide turn. It's a huge problem when there's an optional right-turn lane because people in the far right lane don't even look as they cut left.

[jakeroot]

I feel inclined to point out that not all of these double permissive turns always return to permissive mode. Sometimes, they are protected-only during the day, and permissive-only at night, when the traffic is so light (one or two cars at most per cycle), it's a waste to make the turn lanes protected-only. (In other words, the two lanes are only helpful during rush hour -- other times of the day, they're overkill, so the lights go permissive instead).

[riiga]

I feel inclined to point out that not all of these double permissive turns always return to permissive mode. Sometimes, they are protected-only during the day, and permissive-only at night, when the traffic is so light (one or two cars at most per cycle), it's a waste to make the turn lanes protected-only. (In other words, the two lanes are only helpful during rush hour -- other times of the day, they're overkill, so the lights go permissive instead).

Couldn't you just keep them protected then? You get the safety benefit of proteced signals, and outside of rush hour lights here at least operate on demand with induction loops, I can count on my fingers the number of times I've had to wait at a red light because no one was coming.

[UCFKnights]

I feel inclined to point out that not all of these double permissive turns always return to permissive mode. Sometimes, they are protected-only during the day, and permissive-only at night, when the traffic is so light (one or two cars at most per cycle), it's a waste to make the turn lanes protected-only. (In other words, the two lanes are only helpful during rush hour -- other times of the day, they're overkill, so the lights go permissive instead).

Couldn't you just keep them protected then? You get the safety benefit of proteced signals, and outside of rush hour lights here at least operate on demand with induction loops, I can count on my fingers the number of times I've had to wait at a red light because no one was coming.

Having to stop is still disruptive, bad for the environment, and increases wear on vehicles. In areas without permissive signals (whether because of dual left turn lanes or otherwise), I'm constantly stopped at night as one person pulls into the left turn lane while I'm travelling down at 55mph straight. And of course, when I do eventually want to turn, I have to stop even though there is very clearly no oncoming traffic. If its safe, why make people stop at all?

I know living in Orlando, the most dangerous intersections are the ones with the protected lefts. Everyday, I see people running the red lights because they don't want to have to wait another 4 minutes to make their turn. The permissive signals eliminate that anxiety and fear as there is a chance they can make the turn sooner. I know thats my reaction... if its turning red, rush through the light, if its going permissive, I can wait as I can go in a gap in traffic and won't have to wait for every other phase of the cycle.

[mrsman]

How about a dual permissive left turn with no traffic light at all.

From Los Angeles:

https://www.google.com/maps/@34.0417063,-118.2398621,3a,75y,336.11h,75.71t/data=!3m6!1e1!3m4!1s8L44gMXtW1wcReBFp6CpHQ!2e0!7i13312!8i6656!6m1!1e1

Here on the outskirts of Downtown LA, traffic from Whittier Blvd crosses the LA River (well, not now as the bridge is being replaced) and continues onto 6th Street.  At Central, 6th is one-way eastbound, so westbound traffic must turn right onto Central and then left onto 5th.  5th/Central is a T-intersection, with 5th being a one-way going away from the T.  The main stream of traffic is northbound Central turning left onto 5th.  Southbound Central has a stop sign, and they must yield to all the turning traffic.

I don't like this setup and would prefer a light at this intersection.  The left turn could be the dominant phase, but it would be much safer if southbound Central had their own light.

[roadfro]

^ That's more of a "free left" situation, since the left turn direction is not controlled and the opposing direction has a stop sign.

[Brandon]

Not an uncommon situation where there are Michigan Lefts: https://goo.gl/maps/DmrwcjyWDXs

[jakeroot]

Not an uncommon situation where there are Michigan Lefts: https://goo.gl/maps/DmrwcjyWDXs

I don't think that's necessarily the same thing (although they are related).

[cl94]

Not an uncommon situation where there are Michigan Lefts: https://goo.gl/maps/DmrwcjyWDXs

Those are protected by default because there is no oncoming traffic and no pedestrians. Isn't the same.

[74/171FAN]

Here is one I found on NC 42 in Garner a few years back.  This is at Cleveland Rd just west of I-40 (Exit 312).

[Jovet]

I have not seen one of these, but I echo the sentiments of others:  protected left turns are complicated enough for many drivers... permissive tandem turn lanes are not a safe move.  I'd motion for their banishment, if I were in charge of rulemaking.

[Tom958]

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.

They're replacing it with a protected phase. Oh, well, it was nice while it lasted. 

[Brandon]

Here's another one: https://goo.gl/maps/nwaCg11bp5H2

[roadfro]

Here's another one: https://goo.gl/maps/nwaCg11bp5H2

Is that a permitted left though? Looks like it could be a split phase setup just using 5-aspect heads, due to the shared lane... In street view, it only shows as either red or green arrow+ball (with red for opposing traffic) in all time views, so this seems like a split phase.

If it is a permitted setup, that's rarely a good idea to have a protected/permitted left with a shared lane...that can hinder throughput.

[cl94]

Here's another one: https://goo.gl/maps/nwaCg11bp5H2

Is that a permitted left though? Looks like it could be a split phase setup just using 5-aspect heads, due to the shared lane... In street view, it only shows as either red or green arrow+ball (with red for opposing traffic) in all time views, so this seems like a split phase.

If it is a permitted setup, that's rarely a good idea to have a protected/permitted left with a shared lane...that can hinder throughput.

MUTCD actually prohibits using a shared left turn lane for a dual left if it isn't split phasing. Of course, you get places like the Adirondacks which violate this, but the installation posted in this thread may date to before the restriction was put in place.

[Big John]

^^ Another one in Green Bay: https://www.google.com/maps/@44.5249833,-88.0892947,3a,75y,7.03h,76.94t/data=!3m6!1e1!3m4!1sCbe9JUZaXVcWYd9jakNIrw!2e0!7i13312!8i6656  Worse is that if you want to go straight (though not many do), your only option is the middle shared lane where you may be stuck behind someone trying to make a left turn.  There is a sign there saying left turn yield on green.

[Brandon]

Here's another one: https://goo.gl/maps/nwaCg11bp5H2

Is that a permitted left though? Looks like it could be a split phase setup just using 5-aspect heads, due to the shared lane... In street view, it only shows as either red or green arrow+ball (with red for opposing traffic) in all time views, so this seems like a split phase.

If it is a permitted setup, that's rarely a good idea to have a protected/permitted left with a shared lane...that can hinder throughput.

It's very much a permitted setup with a green for the other direction.  I've been through it many, many times, but it's never all that busy.

[roadfro]

Here's another one: https://goo.gl/maps/nwaCg11bp5H2

Is that a permitted left though? Looks like it could be a split phase setup just using 5-aspect heads, due to the shared lane... In street view, it only shows as either red or green arrow+ball (with red for opposing traffic) in all time views, so this seems like a split phase.

If it is a permitted setup, that's rarely a good idea to have a protected/permitted left with a shared lane...that can hinder throughput.

It's very much a permitted setup with a green for the other direction.  I've been through it many, many times, but it's never all that busy.

Does the signal ever display the green ball alone without the arrow? I didn't see evidence of this in Street View.

[Brandon]

Here's another one: https://goo.gl/maps/nwaCg11bp5H2

Is that a permitted left though? Looks like it could be a split phase setup just using 5-aspect heads, due to the shared lane... In street view, it only shows as either red or green arrow+ball (with red for opposing traffic) in all time views, so this seems like a split phase.

If it is a permitted setup, that's rarely a good idea to have a protected/permitted left with a shared lane...that can hinder throughput.

It's very much a permitted setup with a green for the other direction.  I've been through it many, many times, but it's never all that busy.

Does the signal ever display the green ball alone without the arrow? I didn't see evidence of this in Street View.

Yes, it does.  There's not usually a lot of traffic coming from the other direction, but it does have the green without the arrow.

[UCFKnights]

Here's another one: https://goo.gl/maps/nwaCg11bp5H2

Is that a permitted left though? Looks like it could be a split phase setup just using 5-aspect heads, due to the shared lane... In street view, it only shows as either red or green arrow+ball (with red for opposing traffic) in all time views, so this seems like a split phase.

If it is a permitted setup, that's rarely a good idea to have a protected/permitted left with a shared lane...that can hinder throughput.

MUTCD actually prohibits using a shared left turn lane for a dual left if it isn't split phasing. Of course, you get places like the Adirondacks which violate this, but the installation posted in this thread may date to before the restriction was put in place.

How is that meant to be interpreted (or enforced)? Is the center lane permissive left while the left is protected?

[Brandon]

Here's another one: https://goo.gl/maps/nwaCg11bp5H2

Is that a permitted left though? Looks like it could be a split phase setup just using 5-aspect heads, due to the shared lane... In street view, it only shows as either red or green arrow+ball (with red for opposing traffic) in all time views, so this seems like a split phase.

If it is a permitted setup, that's rarely a good idea to have a protected/permitted left with a shared lane...that can hinder throughput.

MUTCD actually prohibits using a shared left turn lane for a dual left if it isn't split phasing. Of course, you get places like the Adirondacks which violate this, but the installation posted in this thread may date to before the restriction was put in place.

How is that meant to be interpreted (or enforced)? Is the center lane permissive left while the left is protected?

Both of those lanes are permissive, and the signal dates to at least the 1970s like that.