Has the flashing yellow left turn signal made it to your state?

[SignBridge]

mrsman, thanks for posting that info on L.A. City traffic signal engineering. Years ago when I traveled thru Los Angeles several times I did notice that there were not a lot of turning arrows in the city. I wondered about it at the time.

Jakeroot, your analysis of throughput at intersections is interesting and informative and good food for thought. One thing you may be overlooking though, is that turning with an arrow is inherently safer, even at the expense of less throughput. Drivers waiting for a gap to turn are the ones who get impatient and turn in front of oncoming traffic causing accidents. That may be an over-simplification but I believe it's a significant factor in many accidents. But thanks again for your interesting input.

[SignBridge]

And taking a page from jakeroot's style, a second post on a related matter. It's interesting how different cities and counties in California view the left-turn issue. While L.A. City make not like turn arrows, some places like San Diego and Santa Clara County are just the opposite. In much of the area near San Fran. Intl Airport virtually all intersections have protected left-turns only, much to my surprise. Even intersections that didn't seem to need arrows had protected only set-ups. San Diego was somewhat like that also, with excessive numbers of signal heads in some places too.

One extreme to the other within the same state. It would be interesting to know which cities and counties have fewer left-turning accidents.

[UCFKnights]

Never noticed this until now. FYA left turn signal is installed on a shared left-thru lane. Lee NH.

But LOL, if I was the first car in the lane, I would stop well back from the stop-line, right over the loop so I would get the arrow!

Why? Since when have arrows been required to make a turn? If you're the only one there, just turn in a gap or at the end. Don't be selfish.

^ I've seen installations in Nevada where the through lanes have detector loops just right at the stop bar, but left turn lanes often have two sets of loops so that two cars in the pocket can set off detection. I've also seen installations where there are some detection loops beyond the stop line, in order to detect left turning vehicles that are waiting for a gap during permissive phasing.

Shit, I've seen intersections in parts of WA where video detection systems can see well beyond the stop line. I've had lights that trip from my car just barely nosing into the left turn lane.

Definitely haven't seen one activate when I was waiting to turn, although I always wait in the middle of the junction, well beyond the typical detection points.

There's an intersection in my hometown where the sensor is also placed farther back. It's placed where the left painted arrow is beneath the ONLY marking. Come to think of it, my town is also replacing loop detected with 360 degree cameras for the sensors when new signals will be installed next year. With the limited field of view, would it be possible for the detection zone on these kind of sensors to be placed back farther than at the line? I just wonder if those sensors would be confused if the detection zone is placed farther back with other traffic.

There's a few around me where they're placed farther back as well. Another advantage of placing the sensor farther back in the lane is they usually wait a second or 2 to see if another car will trip it to continue to hold the green arrow. If its placed further back, the signal will figure out the lane is empty a second or 2 earlier, so the yellow can activate while the last car is still in the intersection completing the left turn, instead of after the intersection is fully cleared... shaving a couple seconds off the gap between phases. I've long wished this was the common practice everywhere.

[jakeroot]

Jakeroot, your analysis of throughput at intersections is interesting and informative and good food for thought. One thing you may be overlooking though, is that turning with an arrow is inherently safer, even at the expense of less throughput. Drivers waiting for a gap to turn are the ones who get impatient and turn in front of oncoming traffic causing accidents. That may be an over-simplification but I believe it's a significant factor in many accidents. But thanks again for your interesting input.

I'm not pretending like that's not a potential issue with permissive left turns (and by some accounts, protected only lefts can actually increase accident rates), but it's nowhere near a total end-all argument against permissive lefts, and certainly not an argument against a reduction in how often protected phasing is activated at left turns. If anything, it's an argument in favour of modification if/when necessary after a signal is installed. LA, for example, was heavily against protected turns because of close signal spacing and the priority favouring throughput over all else.

Should be noted that, in LA, where left turn phasing is very similar to how I prefer signals to be setup, it's not exactly a sea of traffic collisions compared to adjacent cities and counties.

And taking a page from jakeroot's style, a second post on a related matter. It's interesting how different cities and counties in California view the left-turn issue. While L.A. City make not like turn arrows, some places like San Diego and Santa Clara County are just the opposite. In much of the area near San Fran. Intl Airport virtually all intersections have protected left-turns only, much to my surprise. Even intersections that didn't seem to need arrows had protected only set-ups. San Diego was somewhat like that also, with excessive numbers of signal heads in some places too.

One extreme to the other within the same state. It would be interesting to know which cities and counties have fewer left-turning accidents.

From my reading (from the linked PDF), it's not only that the City of LA had a totally different mindset for left turn phasing (thanks to signal spacing), but also that the city lacked the infrastructure necessary for dedicated left turn signals. Early mast arms were not long enough for dedicated left turn signals, and medians wide enough to support left turn signals were relatively rare in LA proper compared to neighboring counties with their wider suburban-style arterials.

[Bitmapped]

Has anyone seen a FLYA used with a left/straight-through option lane setup before?

In Bridgeville, PA, the intersection of PA 50 and Steen Road is getting a new signal. It's installed, but not in service yet. PA 50 is two lanes in each direction, with no dedicated turn lane.

For PA 50 eastbound traffic, the new signal has three heads: a 4-section FLYA for the left turn movement and two 3-section heads for the straight-through movement. I really don't like having a dedicated left turn head like this because it implies there's a dedicated turn lane when there's not. (The FLYA head is actually mounted left of the center of the roadway.) The intersection before this has a doghouse for an option lane situation, which is common enough, but I really don't like this FLYA usage.

[fwydriver405]

For PA 50 eastbound traffic, the new signal has three heads: a 4-section FLYA for the left turn movement and two 3-section heads for the straight-through movement. I really don't like having a dedicated left turn head like this because it implies there's a dedicated turn lane when there's not. (The FLYA head is actually mounted left of the center of the roadway.) The intersection before this has a doghouse for an option lane situation, which is common enough, but I really don't like this FLYA usage.

Is this example in Skowhegan ME what you are talking about? That intersection in Skowhegan isn't even programmed correctly for proper FYA usage.

[thenetwork]

The real model for great signal progression is the Detroit area.  Tradephoric and others have posted videos showing drivers being able to driving distances of several miles only stopping at red lights a couple of times.  This is true along several corridors Woodward and telegraph being the most famous.  The secret in Detroit for their success are prohibiting most left turns entirely at Major intersections by implementing the so-called Michigan left.  Since you go beyond the intersection 2 then make a u-turn and then a right turn to complete a left turn, you only need to have two separate signal phases at the main intersection.  The proof is in the pudding because signal progression is great over there.

Other factors as to why Metro Detroit signals run near-flawlessly:

-  Speeds on the main roads are usually kept constant -- 40-45 MPH, which makes light synchronization easier to accomplish.
-  They don't just put traffic signals everywhere they think they need one.  In Livonia, for example, besides the signals at the one-mile crossroads, many of the signals are "mid-block" (1/2 mile), and at Michigan Lefts, but seldom anywhere else.  This maintains natural "gaps" in mainline traffic so other side streets and businesses have ample opportunities to turn onto the road.
-  They also seem to encourage left turns to turn into the center turn lane first, then signal into the through lane(s) a bit better than in other parts of the country.

It also helps that most of Metro Detroit designed their roads with the future in mind -- multiple wide lanes, effective commercial zoning laws keeping the busiest retail areas near the main crossroads, 45 MPH limits to allow for better traffic flow, etc...

[Bitmapped]

For PA 50 eastbound traffic, the new signal has three heads: a 4-section FLYA for the left turn movement and two 3-section heads for the straight-through movement. I really don't like having a dedicated left turn head like this because it implies there's a dedicated turn lane when there's not. (The FLYA head is actually mounted left of the center of the roadway.) The intersection before this has a doghouse for an option lane situation, which is common enough, but I really don't like this FLYA usage.

Is this example in Skowhegan ME what you are talking about? That intersection in Skowhegan isn't even programmed correctly for proper FYA usage.

Yes. The PA 50 setup is like that one.

[johndoe]

Good discussion, it reminded me of a thread from a while back.  The whole thing is good, but of course my post is most important to read  https://www.aaroads.com/forum/index.php?topic=22643.msg2320170#msg2320170

Again, along corridors keep in mind lead/lag is usually selected to optimize two-way progression (look up time space diagrams if you really want to dive into the topic).  To illustrate this, you'll likely experience the same signal operate with a different sequences at different times of day (because of volumes, cycle lengths, etc.)  Most places aren't as ideal as the Detroit example, so the spacing, driveways, speeds, etc will all make signal progression tricky.

Regarding where detectors are placed, that's one reason some practitioners don't like loops.  Video zones, for instance, can be modified much quicker than loops.  Maybe you want to test out moving the detection zone to skip some protected phases.  That would take more time and money with loops (bigger maintenance effort to recut the pavement).  On the flip side it's the year 2020 and video detection still gets tricked by shadows, rain, snow, etc. 

[tradephoric]

The real model for great signal progression is the Detroit area.  Tradephoric and others have posted videos showing drivers being able to driving distances of several miles only stopping at red lights a couple of times.  This is true along several corridors Woodward and telegraph being the most famous.  The secret in Detroit for their success are prohibiting most left turns entirely at Major intersections by implementing the so-called Michigan left.  Since you go beyond the intersection 2 then make a u-turn and then a right turn to complete a left turn, you only need to have two separate signal phases at the main intersection.  The proof is in the pudding because signal progression is great over there.
Nexus 5X

Here is an aerial that compares a mile section of a traditional roadway to a mile section of a Michigan left corridor.  The red dots represent traffic signals that stop BOTH directions of travel while the green dots stop only one direction of travel.  While there are more traffic signals along the Michigan left corridor only 2 of them stop both directions of travel compared to 5 traffic signals that stop both directions along the traditional roadway. 



Here's another example.  Along a 10 mile stretch of Big Beaver (Michigan left corridor) there are only 11 signals that stop both directions of travel.  Compare that to 22 signals that stop both directions of travel along Maple Road (traditional corridor).  Big Beaver is smooth sailing signal progression while Maple is stop-and-go signal progression.

[jakeroot]

I fully understand why Detroit gets brought up when the discussion of signal progression does, although I'm really hesitant to actually acknowledge Detroit given how non-translatable the U-turn concept is, for most other cities.

Detroit, simply put, has incredibly wide ROWs, far wider than the vast majority of roads in the vast majority of cities. When you see cities try and replicate it, you end up having some unbelievably elaborate intersections with, more often than not, single lane U-turn maneuvers and almost always traffic must wait for a green arrow. Plus, unlike in Detroit, other cities almost always have to bulb out their U-turn points; Detroit's wider ROW does not require this, with the turns more like tighter left turns, with the ability to allow the turn on red, even with multiple turn lanes.

For me, I guess I just find it more interesting to look at improvements to "regular" intersections with dedicated left turn lanes, since spot improvements for those types of intersections are more easily replicated.

I look at a city like Los Angeles with great admiration because they've made really incredible strides in traffic flow while simultaneously dealing with both significant levels of pedestrian traffic and older, narrower ROW.

As a side-note, given my Urban Design background: although "nobody walks in LA", it seems to be more enjoyable than walking around Detroit's super streets. That's something else to keep in mind when considering the benefits of 200ft ROW

[kphoger]

Yeah, I tire of seeing the same two Detroit-area corridors brought up as something other cities should emulate.  The environment that allows those corridors to work well can hardly be found elsewhere.

[mrsman]

jakeroot's most recent GSV link form Utah demonstrated something really interesting.  In the midst of the Michigan-left corridor you have an intersection with a frontage road.  The intersection has only two signal phases:  main street and second phase.  During the second phase, the frontage road gets a protected right turn (only right turns are allowed), the main street gets a protected left onto the frontage road (no u-turn), and pedestrians can cross the main street via one of the diagonals.  This is an extremely unique situation.

https://www.google.com/maps/@41.075071,-111.9745658,3a,75y,68.96h,76.97t/data=!3m6!1e1!3m4!1s2aFDxeLsiRPdNrY-Lp9QvA!2e0!7i13312!8i6656

[roadfro]

jakeroot's most recent GSV link form Utah demonstrated something really interesting.  In the midst of the Michigan-left corridor you have an intersection with a frontage road.  The intersection has only two signal phases:  main street and second phase.  During the second phase, the frontage road gets a protected right turn (only right turns are allowed), the main street gets a protected left onto the frontage road (no u-turn), and pedestrians can cross the main street via one of the diagonals.  This is an extremely unique situation.

https://www.google.com/maps/@41.075071,-111.9745658,3a,75y,68.96h,76.97t/data=!3m6!1e1!3m4!1s2aFDxeLsiRPdNrY-Lp9QvA!2e0!7i13312!8i6656

That is a really unique situation, and I rather like it. Even though it is a tad complex/unusual from the motorist perspective, it's still in essence what is often referred to as a "two-phase" signal. Only down side is that long diagonal pedestrian crossing–seems like it could be inconvenient for pedestrians, and a bit of a drag on throughput for through traffic if there's a ped call and no simultaneous turning vehicles.

[mrsman]

jakeroot's most recent GSV link form Utah demonstrated something really interesting.  In the midst of the Michigan-left corridor you have an intersection with a frontage road.  The intersection has only two signal phases:  main street and second phase.  During the second phase, the frontage road gets a protected right turn (only right turns are allowed), the main street gets a protected left onto the frontage road (no u-turn), and pedestrians can cross the main street via one of the diagonals.  This is an extremely unique situation.

https://www.google.com/maps/@41.075071,-111.9745658,3a,75y,68.96h,76.97t/data=!3m6!1e1!3m4!1s2aFDxeLsiRPdNrY-Lp9QvA!2e0!7i13312!8i6656

That is a really unique situation, and I rather like it. Even though it is a tad complex/unusual from the motorist perspective, it's still in essence what is often referred to as a "two-phase" signal. Only down side is that long diagonal pedestrian crossing–seems like it could be inconvenient for pedestrians, and a bit of a drag on throughput for through traffic if there's a ped call and no simultaneous turning vehicles.

Yes, I imagine because it is a very long crossing, the amount of time for peds to cross is probably very high.  Yet, given that it is right next to a freeway, there probably aren't too many pedestrians there.

[tradephoric]

Yeah, I tire of seeing the same two Detroit-area corridors brought up as something other cities should emulate.  The environment that allows those corridors to work well can hardly be found elsewhere.

There are hundreds of miles of Median U-turn corridor in Metro Detroit.  Woodward and Telegraph may be the best examples due to their sheer length but many more exist.  You could also include New Orleans as a city with wide medians that have variations of the Michigan Left turn.  But outside of New Orleans and Detroit are Median U-turn corridors practical?  To be honest not really.  Tuscon is attempting a Median U-turn corridor along Grant Road but it's only so practical (and requires a lot of costly ROW acquisition for all the bulb outs).

[jakeroot]

jakeroot's most recent GSV link form Utah demonstrated something really interesting.  In the midst of the Michigan-left corridor you have an intersection with a frontage road.  The intersection has only two signal phases:  main street and second phase.  During the second phase, the frontage road gets a protected right turn (only right turns are allowed), the main street gets a protected left onto the frontage road (no u-turn), and pedestrians can cross the main street via one of the diagonals.  This is an extremely unique situation.

https://www.google.com/maps/@41.075071,-111.9745658,3a,75y,68.96h,76.97t/data=!3m6!1e1!3m4!1s2aFDxeLsiRPdNrY-Lp9QvA!2e0!7i13312!8i6656

That is a really unique situation, and I rather like it. Even though it is a tad complex/unusual from the motorist perspective, it's still in essence what is often referred to as a "two-phase" signal. Only down side is that long diagonal pedestrian crossing–seems like it could be inconvenient for pedestrians, and a bit of a drag on throughput for through traffic if there's a ped call and no simultaneous turning vehicles.

Yes, I imagine because it is a very long crossing, the amount of time for peds to cross is probably very high.  Yet, given that it is right next to a freeway, there probably aren't too many pedestrians there.

And to me, from the perspective of urban design, "good infrastructure" should naturally accommodate pedestrian movements while simultaneously allowing for relatively good vehicular movement. It seems like a lot of these alternative intersection designs fall apart when traffic signal engineers have to program a pedestrian phase. The longest phase is almost always going to be the longest movement, and the longest movement is almost always across the widest road, which is usually the busiest road. Los Angeles, though it doesn't always, can much more easily accommodate pedestrians because most intersections are relatively simple. The PDF from earlier discusses how LADOT programmed auto-walk displays on Sabbath for the Jewish community. They don't do it city-wide, but it highlights how easily "regular" road infrastructure can be adjusted to accommodate all users.

[mrsman]

jakeroot's most recent GSV link form Utah demonstrated something really interesting.  In the midst of the Michigan-left corridor you have an intersection with a frontage road.  The intersection has only two signal phases:  main street and second phase.  During the second phase, the frontage road gets a protected right turn (only right turns are allowed), the main street gets a protected left onto the frontage road (no u-turn), and pedestrians can cross the main street via one of the diagonals.  This is an extremely unique situation.

https://www.google.com/maps/@41.075071,-111.9745658,3a,75y,68.96h,76.97t/data=!3m6!1e1!3m4!1s2aFDxeLsiRPdNrY-Lp9QvA!2e0!7i13312!8i6656

That is a really unique situation, and I rather like it. Even though it is a tad complex/unusual from the motorist perspective, it's still in essence what is often referred to as a "two-phase" signal. Only down side is that long diagonal pedestrian crossing–seems like it could be inconvenient for pedestrians, and a bit of a drag on throughput for through traffic if there's a ped call and no simultaneous turning vehicles.

Yes, I imagine because it is a very long crossing, the amount of time for peds to cross is probably very high.  Yet, given that it is right next to a freeway, there probably aren't too many pedestrians there.

And to me, from the perspective of urban design, "good infrastructure" should naturally accommodate pedestrian movements while simultaneously allowing for relatively good vehicular movement. It seems like a lot of these alternative intersection designs fall apart when traffic signal engineers have to program a pedestrian phase. The longest phase is almost always going to be the longest movement, and the longest movement is almost always across the widest road, which is usually the busiest road. Los Angeles, though it doesn't always, can much more easily accommodate pedestrians because most intersections are relatively simple. The PDF from earlier discusses how LADOT programmed auto-walk displays on Sabbath for the Jewish community. They don't do it city-wide, but it highlights how easily "regular" road infrastructure can be adjusted to accommodate all users.

I think another aspect as to why the LADOT was easy to accommodate the Sabbath signaling was that for the most part it affected traffic on a low traffic day (Saturday).  Yes, there are some Jewish holidays that occur on weekdays, but they are only a few of them  - so most weekday and rush hour traffic remain unaffected by it.  Plus, if a significant number of residents in that neighborhood are observing Sabbath or a Jewish holiday (and hence not driving) the traffic counts are lower for that neighborhood, even if there is no significant change in traffic counts citywide.

That being said, I think you're right that if a pedestrian is there in Utah, all of the modeling will fall apart. The signal delay on the main road would be substantial whenever a pedestrian is detected. Fortunately, the amount of crossing there is probably very low so the actual effects on traffic aren't present on a regular basis.

[kphoger]

Yes, I imagine because it is a very long crossing, the amount of time for peds to cross is probably very high.  Yet, given that it is right next to a freeway, there probably aren't too many pedestrians there.

Pedestrian paths across a very wide road are especially intimidating for blind pedestrians, who–not being able to drive–may need to cross such a road before or after a trip on a city bus.  This tends to be especially problematic at shopping centers, because they generally are both (1) places people need to get to and (2) near busy, wide roads.

For example, if a blind couple from Kaysville used public transit to go out on a date at Denny's or the Olive Garden, then they might reasonably use that crosswalk afterwards to catch bus #627 back home.  (Yes, it would be a shorter walk to catch the bus in front of Dillon's, but there's a noticeable lack of sidewalks along that path.)

[jakeroot]

That being said, I think you're right that if a pedestrian is there in Utah, all of the modeling will fall apart. The signal delay on the main road would be substantial whenever a pedestrian is detected. Fortunately, the amount of crossing there is probably very low so the actual effects on traffic aren't present on a regular basis.

Indeed, there won't be many pedestrians. But it just doesn't seem right to bank on there not being enough pedestrians. Walking is the most basic form of transportation, yet engineers rarely build to accommodate them. Sidewalks are built, sure, but there's more to it than just that. Especially in a country with such strict jaywalking laws.

[webny99]

I am bringing my comment into a second post so that others may consider this specific facet of operation more closely, and ideally, critique my thinking:

Consider that an unspecific intersection has a 120-second total cycle: assuming both roads are equally utilised, that's 60 seconds for each road. If a two-second all red phase is provided, that's 58 seconds for through traffic along both roads. If we implement green arrows at the beginning, that drops to about 50 seconds, with that number dropping further with each additional car turning left. Assuming there is only one or two cars waiting to turn, providing the full 58 seconds for through traffic, and leaving the two-second all-red phase for those two cars to finish their turns, we are providing for the most efficient setup physically possible at a signalized intersection.

Providing a left turn phase at the beginning could reduce the green time for through traffic by around 15 to 20%, if not more. Yet this reduction could potentially exist to allow only one or two cars to turn at the beginning, when they could just as easily turn at the end during an all-red phase (which should exist at all intersections anyways).

The only real issue with my thought process is that, in too many parts of the country, drivers absolutely refuse to enter the intersection during a permissive phase. This stubbornness absolutely harms traffic flow, because engineers basically become forced to provide green arrows for every phase, since drivers who don't enter the intersection will only be able to turn in gaps, at that is certainly no guarantee along busy roads.

Realizing this post is now a week old: I mostly agree, but that bolded statement is a massive assumption. It seems like it would be pretty rare to have so few cars turning. If it really is determined that turning volumes are that low, then a protected phase isn't needed - but that would probably exclude the vast majority of cases.

Here's a generic example in my area - volumes roughly equal on both roads, signal phases roughly equal on both roads, currently permissive-only. There's often 6-8 cars lined up to turn left, and every time I have to wait more than one cycle to turn, which is maybe once a month or so, I'm figuratively wishing there was a protected phase.

Regarding your last paragraph, FYA's aren't common enough in this area yet to say for sure, but it seems like drivers are especially hesitant to turn left when the people next to them, going straight, still have a red light and they have the FYA. I could probably count on one hand the amount of times I've seen them used properly, where someone turns left immediately after the opposing straight traffic has cleared instead of waiting for the opposing protected phase to end.

[jeffandnicole]

Here's a generic example in my area - volumes roughly equal on both roads, signal phases roughly equal on both roads, currently permissive-only. There's often 6-8 cars lined up to turn left, and every time I have to wait more than one cycle to turn, which is maybe once a month or so, I'm figuratively wishing there was a protected phase.

How often would you wind up waiting the entire cycle if it was protected and you just missed the green arrow?  What if the protected length only allowed 5 or 6 cars thru, whereas several more makes it thru now?

Waiting an extra cycle length once a month isn't too bad.  A Protected-Permissive green arrow would be the better option.

[jakeroot]

I am bringing my comment into a second post so that others may consider this specific facet of operation more closely, and ideally, critique my thinking:

Consider that an unspecific intersection has a 120-second total cycle: assuming both roads are equally utilised, that's 60 seconds for each road. If a two-second all red phase is provided, that's 58 seconds for through traffic along both roads. If we implement green arrows at the beginning, that drops to about 50 seconds, with that number dropping further with each additional car turning left. Assuming there is only one or two cars waiting to turn, providing the full 58 seconds for through traffic, and leaving the two-second all-red phase for those two cars to finish their turns, we are providing for the most efficient setup physically possible at a signalized intersection.

Providing a left turn phase at the beginning could reduce the green time for through traffic by around 15 to 20%, if not more. Yet this reduction could potentially exist to allow only one or two cars to turn at the beginning, when they could just as easily turn at the end during an all-red phase (which should exist at all intersections anyways).

The only real issue with my thought process is that, in too many parts of the country, drivers absolutely refuse to enter the intersection during a permissive phase. This stubbornness absolutely harms traffic flow, because engineers basically become forced to provide green arrows for every phase, since drivers who don't enter the intersection will only be able to turn in gaps, at that is certainly no guarantee along busy roads.

Realizing this post is now a week old: I mostly agree, but that bolded statement is a massive assumption. It seems like it would be pretty rare to have so few cars turning. If it really is determined that turning volumes are that low, then a protected phase isn't needed - but that would probably exclude the vast majority of cases.

Here's a generic example in my area - volumes roughly equal on both roads, signal phases roughly equal on both roads, currently permissive-only. There's often 6-8 cars lined up to turn left, and every time I have to wait more than one cycle to turn, which is maybe once a month or so, I'm figuratively wishing there was a protected phase.

You need to read the entirety of my post. I am considering a hypothetical situation where a traffic light has only one or two cars in a left turn lane, and how, operationally, it would work much better without a green arrow at the beginning. I think it's fair to assume that having three or more cars stacked up in every left turn lane at every single intersection is fairly rare. Besides, the number of cars grows less and less relevant the more gaps become available. Assuming there is no gaps, two cars can turn at the end of every cycle. Thus, activating a left turn for less than three cars is not necessary. If more cars arrive, then a green arrow can activate at the beginning of the next cycle (assuming there is enough remaining vehicles); alternatively, a lagging green arrow could be implemented.

Looking at your example, the fact that you need an extra cycle to turn only once a month is a testament to how efficient the intersection is, frankly. Consider how much capacity might be lost for through traffic if a green arrow were added? Especially one that activated for a single car.

Regarding your last paragraph, FYA's aren't common enough in this area yet to say for sure, but it seems like drivers are especially hesitant to turn left when the people next to them, going straight, still have a red light and they have the FYA. I could probably count on one hand the amount of times I've seen them used properly, where someone turns left immediately after the opposing straight traffic has cleared instead of waiting for the opposing protected phase to end.

Hmm. That definitely has not been my experience in Washington. The left-facing arrows should make its purpose fairly clear. If they don't go when the through traffic is red, so be it. At least they'll go once the through signal turns green, or until a driver who understands the meaning of a left turn signal beeps at them

[mrsman]

I am bringing my comment into a second post so that others may consider this specific facet of operation more closely, and ideally, critique my thinking:

Consider that an unspecific intersection has a 120-second total cycle: assuming both roads are equally utilised, that's 60 seconds for each road. If a two-second all red phase is provided, that's 58 seconds for through traffic along both roads. If we implement green arrows at the beginning, that drops to about 50 seconds, with that number dropping further with each additional car turning left. Assuming there is only one or two cars waiting to turn, providing the full 58 seconds for through traffic, and leaving the two-second all-red phase for those two cars to finish their turns, we are providing for the most efficient setup physically possible at a signalized intersection.

Providing a left turn phase at the beginning could reduce the green time for through traffic by around 15 to 20%, if not more. Yet this reduction could potentially exist to allow only one or two cars to turn at the beginning, when they could just as easily turn at the end during an all-red phase (which should exist at all intersections anyways).

The only real issue with my thought process is that, in too many parts of the country, drivers absolutely refuse to enter the intersection during a permissive phase. This stubbornness absolutely harms traffic flow, because engineers basically become forced to provide green arrows for every phase, since drivers who don't enter the intersection will only be able to turn in gaps, at that is certainly no guarantee along busy roads.

Realizing this post is now a week old: I mostly agree, but that bolded statement is a massive assumption. It seems like it would be pretty rare to have so few cars turning. If it really is determined that turning volumes are that low, then a protected phase isn't needed - but that would probably exclude the vast majority of cases.

Here's a generic example in my area - volumes roughly equal on both roads, signal phases roughly equal on both roads, currently permissive-only. There's often 6-8 cars lined up to turn left, and every time I have to wait more than one cycle to turn, which is maybe once a month or so, I'm figuratively wishing there was a protected phase.

You need to read the entirety of my post. I am considering a hypothetical situation where a traffic light has only one or two cars in a left turn lane, and how, operationally, it would work much better without a green arrow at the beginning. I think it's fair to assume that having three or more cars stacked up in every left turn lane at every single intersection is fairly rare. Besides, the number of cars grows less and less relevant the more gaps become available. Assuming there is no gaps, two cars can turn at the end of every cycle. Thus, activating a left turn for less than three cars is not necessary. If more cars arrive, then a green arrow can activate at the beginning of the next cycle (assuming there is enough remaining vehicles); alternatively, a lagging green arrow could be implemented.

Looking at your example, the fact that you need an extra cycle to turn only once a month is a testament to how efficient the intersection is, frankly. Consider how much capacity might be lost for through traffic if a green arrow were added? Especially one that activated for a single car.

Regarding your last paragraph, FYA's aren't common enough in this area yet to say for sure, but it seems like drivers are especially hesitant to turn left when the people next to them, going straight, still have a red light and they have the FYA. I could probably count on one hand the amount of times I've seen them used properly, where someone turns left immediately after the opposing straight traffic has cleared instead of waiting for the opposing protected phase to end.

Hmm. That definitely has not been my experience in Washington. The left-facing arrows should make its purpose fairly clear. If they don't go when the through traffic is red, so be it. At least they'll go once the through signal turns green, or until a driver who understands the meaning of a left turn signal beeps at them

Another thing to keep in mind, of course, is that for any given intersection, the number of cars waiting to turn left will change based on time of day and day of the week.  An intersection that may have a really busy left turn at rush hour may only service one or two cars at 10 pm.  The rush hour traffic load will dictate that a left turn signal be implemented, but the 10 pm traffic load would indicate that the left turn signal should not be activated at such time.

It is true as mentioned above, that in most cases, the sensor equipment cannot distinguish how many cars are waiting in the left turn lane so the left turn signal will turn on even when there is only one car waiting.  The exceptions occur in cases (like Los Angeles) where multiple sensors are placed along the left turn lane or if a strict time of day phasing is employed (but that could have worse results as real world conditions would not change the timing).

[webny99]

How often would you wind up waiting the entire cycle if it was protected and you just missed the green arrow?  What if the protected length only allowed 5 or 6 cars thru, whereas several more makes it thru now?
Waiting an extra cycle length once a month isn't too bad.  A Protected-Permissive green arrow would be the better option.

Looking at your example, the fact that you need an extra cycle to turn only once a month is a testament to how efficient the intersection is, frankly. Consider how much capacity might be lost for through traffic if a green arrow were added? Especially one that activated for a single car.

Should have specified this originally, but for context, I only turn left here once in a while, maybe a couple times per month, but it varies. It seems to be close to a coin-flip, regardless of which direction you're going, as to whether you'll have to wait one cycle or two.

I'm not advocating protected-only - those can be just as frustrating, especially for a standard intersection with speeds usually below 50 mph and no other dangerous features why permissive shouldn't be allowed. I'm a protected/permissive fan, so naturally that's what I'd like to see here.