Alternatives to the flashing yellow arrow

[Brandon]

With the FYA you still have left turn phases which prevents any significant gains in capacity.   

But traffic is also able to turn left outside of the left turn phases, so in intersections that went from protected-only to FYI, the volume of turning vehicles increased.

No they did not.  These intersections were protected/permissive before.  All they did was to go from the flashing red ball to the flashing yellow arrow.  Thus, there was zero gain in volume.

Do you honestly believe that making traffic stop before turning has the same capacity as making traffic simply yield?

In practice, as stated by Tradephoric above, no one, not even cops, stops at the flashing red ball to make a left turn in Michigan.

[jakeroot]

With the FYA you still have left turn phases which prevents any significant gains in capacity.   

But traffic is also able to turn left outside of the left turn phases, so in intersections that went from protected-only to FYI, the volume of turning vehicles increased.

No they did not.  These intersections were protected/permissive before.  All they did was to go from the flashing red ball to the flashing yellow arrow.  Thus, there was zero gain in volume.

Do you honestly believe that making traffic stop before turning has the same capacity as making traffic simply yield?

In practice, as stated by Tradephoric above, no one, not even cops, stops at the flashing red ball to make a left turn in Michigan.

Well, as also stated by Tradephoric above, the amount of injury collisions is back to pre-FYA levels, so why are we still having this conversation?

[roadfro]

If you go back to my original post, I concluded that a change to allow a flashing green would not be wise at this point because the meaning of flashing yellow is already ingrained.  But the point that I was trying to make was that if there were a separate signal indication for yield without stopping, the FYA would be more intuitive. 

I'm not aware that people are really confusing the FYA with the possibility that left turners actually have the right of way when the FYA is displayed.  I think the biggest problem is that the FYA is ignored and that the "yellow trap" problem is not really resolved.  Left turners will see the FYA but they will also see that  adjacent traffic gets a yellow ball and they would assume that both adjacent and opposing traffic sees the yellow ball (and thus will soon see a red ball).  This is ingrained in most drivers and is dangerously incorrect in a FYA controlled lead-lag intersection.

I think that a protected/permissive lagging left is dangerous and leads to a yellow trap unless the opposing left is: 1) also lagging at the same time, 2) prohibited by law, or 3) protected only leading left (red arrow).  The signal indication is irrelevant.

And if we don't need to incorporate a lead-lag protected/permitted left, we don't need a FYA when the doghouse signal works just fine.

A "yield" condition assigns right-of-way to traffic on certain approaches to an intersection--vehicles controlled by a YIELD need to slow down to a speed that is reasonable for the existing conditions or stop when necessary to avoid interfering with conflicting traffic (that's a paraphrase from the MUTCD). So "Yield without stopping" doesn't actually make sense. However, I get the point you are trying to make, and in that sense I can see where a flashing green (as a substitute for yellow in red/yellow flash mode) could draw the distinction--still not sold on it though.

The FYA does eliminate "yellow trap", but does introduce "perceived yellow trap" if a driver is paying attention to the adjacent through signals when trying to make the permitted left turn. The main question is why the driver bothers paying attention to the adjacent through signals at all when faced with an all-arrow display. I don't get why that concept isn't ingrained in driver's heads... Lead/lag PPLT has been used without major issue in many locations (Dallas, Las Vegas, among others).

The all-arrow FYA display over dedicated left turn lanes is definitely an improvement over relying on a simple doghouse. It's a much clearer indication.

At some point, reality trumps theory.  The reality is the total number of injury accidents have increased by 30% at new FYA installs throughout SE Michigan.  The "perceived yellow trap" , which was rarely seen under Michigan's old style flashing red ball, is becoming commonplace at FYA intersections throughout the region.  Also, it may have been a mistake to incorporate a flashing yellow arrow as opposed to a flashing red arrow.  A segment of the driving population approaching a flashing yellow arrow will wrongfully assume that they have the right of way (since they equate yellow to mean "Proceed with caution"  or even just "Proceed" ).  From a safety standpoint, the FYA has failed in SE Michigan.  That's the reality.

I make the assumption that all intersections included in this data had flashing circular red PPLT in the before case, and FYA PPLT in the after case. Further, I would hope the data is comparing similar timing and phasing schemes. If either one of those statements is not the case, then the comparison data isn't valid for analysis. If both statements are true, then this truly is a mystery. IIRC, various before/after studies conducted on FYA before it was included in the MUTCD didn't have such results, so what is the issue in Michigan? I would want to speculate that it's the use of a less restrictive color indication, but the assertions that no driver stops at a flashing circular red for PPLTs in Michigan would seem to eliminate that thought...

[tradephoric]

A major 2007 study (NCHRP web only document 123) analyzed the safety benefits of the FYA at over 50 installations.  The following conclusion was made:

The installation of the FYA indication at sites which currently operate PPLT signal phasing showed improvements in safety.  In other locations, the change in left-turn signal phasing had a more significant impact on safety than the change in left-turn indication, although safety appeared to improve with time.

The MDOT FYA brochure (linked on Macomb County's website) describes the FYA as a "safer, more efficient way to handle traffic turning left at busy intersections" .   The FYA brochure makes it sound like a WIN-WIN, where traffic moves more efficiently and safely through an intersection.  This is not the case.  Since the introduction of the FYA in Macomb, the lagging PPLT are allowed to skip if no vehicles are detected (under the old flashing circular red, the lagging PPLT were not allowed to skip).  So yes, the FYA's in Macomb County has led to more efficient operation but it has come at a cost to safety. 

I agree with Roadfro that it's not a fair apples-to-apples comparison.  I just don't feel it's fair to describe the FYA as a safer AND more efficient type of PPLT.  It's either one or the other. 

[roadfro]

I just don't feel it's fair to describe the FYA as a safer AND more efficient type of PPLT.  It's either one or the other.

This is a fair statement.

The safety benefit of the FYA through new signal indications seems to be proven (although perhaps not universally) through various studies and trials. The FYA being better than a circular green in the permissive mode–particularly in instances where drivers reacted to a critical circumstance with a more "fail safe" response.

The efficiency aspect may not necessarily come from the FYA itself. Rather, the FYA has increased awareness in the signal timing and manufacturing community about signal timing/phasing techniques for PPLT operation. Some of the operational come from simple re-timing or now using PPLT where signals were protected-only before. Other operational efficiencies in some jurisdictions are things that could have been done previously but took much more effort than some agencies would expend. For example, tying the permissive mode to the opposing thru movement was something rather complex when first introduced as Dallas Phasing (in Vegas, this required installing a louvered 5-section display and requiring technicians to add special programming to controllers and hardware to achieve the result); with the advent of FYA, PPLT signal hardware is cheaper and the controller logic has been pre-programmed into many newer signal controllers, making it much easier to implement more advanced phasing options.

[froggie]

The year-by-year stats graph tradephoric posted earlier suggests to me that there was a bit of a learning curve with the FYA in that region.  But once Michigan drivers got more used to the FYA, the safety benefits began to show themselves.

[tradephoric]

The year-by-year stats graph tradephoric posted earlier suggests to me that there was a bit of a learning curve with the FYA in that region.  But once Michigan drivers got more used to the FYA, the safety benefits began to show themselves.

There's even a bigger learning curve with roundabouts.  The chart below looks at crash data of 16 major roundabouts built throughout SE Michigan between 2006-2009.  While PDO accidents spike the first year after roundabout construction, injury accidents drop from day one.  There's no doubt that roundabouts reduce injury accidents. 

[doogie1303]

If an intersection's traffic pattern allows for the use of a FYA for turns, then at that point what's the difference between the intersection with a FYA and the intersection with a doghouse signal?

Also why is it that the FYA option requires an addtional head to be added to a dedicated turn signal (red arrow, two yellow arrows, green arrow)? Why can't they just flash the yellow arrows that already exist on the three ways? It would seem easier to install this option in existing equipment without major rewiring and adding an additional head.

[GaryV]

If an intersection's traffic pattern allows for the use of a FYA for turns, then at that point what's the difference between the intersection with a FYA and the intersection with a doghouse signal?

FYA allows for permissive turns at some times of the day and not at others.

Also why is it that the FYA option requires an addtional head to be added to a dedicated turn signal (red arrow, two yellow arrows, green arrow)? Why can't they just flash the yellow arrows that already exist on the three ways? It would seem easier to install this option in existing equipment without major rewiring and adding an additional head.
[/quote]
It was considered safer to have a second yellow head for the "going to be red" phase.  Drivers might miss the flashing yellow turning to solid yellow.  It's less likely to be missed if it switches to a separate signal head.

[Mdcastle]

People are too stupid to know you have to yield turning left on a green ball (yes, really). flashing yellow arrow emphasizes the need to yield.

[cl94]

The issue is that a green arrow, by definition, assigns the right of way to vehicles facing it. With a flashing green, you'd have two greens crossing each other, a very dangerous situation. This is the reason why a flashing green is explicitly prohibited in the MUTCD. A ball only assigns ROW in the straight direction, preventing this.

[mrsman]

For all the pro-FYA people out there,

To what extent would you favor changing split-phasing signals to FYA?

Here is the situation:  A four-way intersection.  Eastbound gets 18 seconds of green (with a left arrow as well), followed by 2 seconds of yellow.  Westbound gets 33 seconds of green followed by 2 seconds of yellow.  Then north/south gets 63 seconds of green followed by 2 seconds of yellow.  The current signal display for eastbound and westbound have a 4-aspect tower: R,Y,G,GA.  Green and green arrow are lit at the same time.  This is pure split phasing.

Could this then be changed to a situation where westbound sees a FYA while eastbound sees green and eastbound sees a FYA while westbound sees green, thereby allowing an optional permissive left turn during the entire time that north/south has a red light?

Would your answer change if there were multiple left turn lanes (or optional left turn lanes) on the eastbound and/or westbound left turns?

[cl94]

For all the pro-FYA people out there,

To what extent would you favor changing split-phasing signals to FYA?

Here is the situation:  A four-way intersection.  Eastbound gets 18 seconds of green (with a left arrow as well), followed by 2 seconds of yellow.  Westbound gets 33 seconds of green followed by 2 seconds of yellow.  Then north/south gets 63 seconds of green followed by 2 seconds of yellow.  The current signal display for eastbound and westbound have a 4-aspect tower: R,Y,G,GA.  Green and green arrow are lit at the same time.  This is pure split phasing.

Could this then be changed to a situation where westbound sees a FYA while eastbound sees green and eastbound sees a FYA while westbound sees green, thereby allowing an optional permissive left turn during the entire time that north/south has a red light?

Would your answer change if there were multiple left turn lanes (or optional left turn lanes) on the eastbound and/or westbound left turns?

Biggest issue is that there's a yellow trap. Heading EB, you don't know the state of the opposing signal (as it is not duplicated in your direction) and might end up causing more issues (yellow trap accidents). If there is a heavy turn movement from the WB movement, in this case, you could theoretically give it an FYA, as WB would be getting a full green afterward. I really don't see a problem with this if the EB movement is pretty light.

[roadfro]

For all the pro-FYA people out there,

To what extent would you favor changing split-phasing signals to FYA?

Here is the situation:  A four-way intersection.  Eastbound gets 18 seconds of green (with a left arrow as well), followed by 2 seconds of yellow.  Westbound gets 33 seconds of green followed by 2 seconds of yellow.  Then north/south gets 63 seconds of green followed by 2 seconds of yellow.  The current signal display for eastbound and westbound have a 4-aspect tower: R,Y,G,GA.  Green and green arrow are lit at the same time.  This is pure split phasing.

Could this then be changed to a situation where westbound sees a FYA while eastbound sees green and eastbound sees a FYA while westbound sees green, thereby allowing an optional permissive left turn during the entire time that north/south has a red light?

Would your answer change if there were multiple left turn lanes (or optional left turn lanes) on the eastbound and/or westbound left turns?

Biggest issue is that there's a yellow trap. Heading EB, you don't know the state of the opposing signal (as it is not duplicated in your direction) and might end up causing more issues (yellow trap accidents). If there is a heavy turn movement from the WB movement, in this case, you could theoretically give it an FYA, as WB would be getting a full green afterward. I really don't see a problem with this if the EB movement is pretty light.

Yellow trap isn't a big issue, as the FYA eliminates the yellow trap regardless of what point in the cycle the permissive/protected phases are, due to flashing yellow overlapping with opposing through green. ("Perceived" yellow trap is a different issue.)

The issue in this particular case relates to the reason for the split phasing to begin with. I'm going to assume that the intersection isn't skewed and that there are no sight distance issues. What is the lane configuration like? If there's any shared turning lanes (i.e. 1 left turn lane and 1 shared left/through lane), then there is no other safe signal phasing option other than to use a split. If there are no shared lanes and each direction has a a single dedicated left turn lane, then a FYA can potentially be installed–most engineers will frown on permissive phasing with multiple turn lanes though for safety reasons.

[mrsman]

For all the pro-FYA people out there,

To what extent would you favor changing split-phasing signals to FYA?

Here is the situation:  A four-way intersection.  Eastbound gets 18 seconds of green (with a left arrow as well), followed by 2 seconds of yellow.  Westbound gets 33 seconds of green followed by 2 seconds of yellow.  Then north/south gets 63 seconds of green followed by 2 seconds of yellow.  The current signal display for eastbound and westbound have a 4-aspect tower: R,Y,G,GA.  Green and green arrow are lit at the same time.  This is pure split phasing.

Could this then be changed to a situation where westbound sees a FYA while eastbound sees green and eastbound sees a FYA while westbound sees green, thereby allowing an optional permissive left turn during the entire time that north/south has a red light?

Would your answer change if there were multiple left turn lanes (or optional left turn lanes) on the eastbound and/or westbound left turns?

Biggest issue is that there's a yellow trap. Heading EB, you don't know the state of the opposing signal (as it is not duplicated in your direction) and might end up causing more issues (yellow trap accidents). If there is a heavy turn movement from the WB movement, in this case, you could theoretically give it an FYA, as WB would be getting a full green afterward. I really don't see a problem with this if the EB movement is pretty light.

Yellow trap isn't a big issue, as the FYA eliminates the yellow trap regardless of what point in the cycle the permissive/protected phases are, due to flashing yellow overlapping with opposing through green. ("Perceived" yellow trap is a different issue.)

The issue in this particular case relates to the reason for the split phasing to begin with. I'm going to assume that the intersection isn't skewed and that there are no sight distance issues. What is the lane configuration like? If there's any shared turning lanes (i.e. 1 left turn lane and 1 shared left/through lane), then there is no other safe signal phasing option other than to use a split. If there are no shared lanes and each direction has a a single dedicated left turn lane, then a FYA can potentially be installed–most engineers will frown on permissive phasing with multiple turn lanes though for safety reasons.

In the example that I'm thinking of, based on a real-world split-phased signal at Dennis/Georgia in Silver Spring, MD, EB has a dedicated single left turn lane.  WB has a dedicated left and an option lane left or straight, but the vast majority of traffic makes a left turn. 

You're right that the reason for the split phasing was probably due to the shared lane treatment.  My question is why is it unsafe to have a permissive left here?  There are plenty of signalized intersections with no left turn lane at all and the left thru lane is a de facto left or straight option lane.  If the car ahead of you wants to turn left, you may have to wait until traffic is clear for him to turn, even if the light is green and even if you want to go straight.  That's the risk of being in the option lane, the car ahead of you (or the car ahead of that car) may want to go a different movement and you may have to wait for him, yet there are too many cars wanting to turn left for one lane to be sufficient.

[roadfro]

In the example that I'm thinking of, based on a real-world split-phased signal at Dennis/Georgia in Silver Spring, MD, EB has a dedicated single left turn lane.  WB has a dedicated left and an option lane left or straight, but the vast majority of traffic makes a left turn. 

You're right that the reason for the split phasing was probably due to the shared lane treatment.  My question is why is it unsafe to have a permissive left here?  There are plenty of signalized intersections with no left turn lane at all and the left thru lane is a de facto left or straight option lane.  If the car ahead of you wants to turn left, you may have to wait until traffic is clear for him to turn, even if the light is green and even if you want to go straight.  That's the risk of being in the option lane, the car ahead of you (or the car ahead of that car) may want to go a different movement and you may have to wait for him, yet there are too many cars wanting to turn left for one lane to be sufficient.

With a single dedicated left turn lane in the EB direction, you could use potentially use permitted left turns for that. However, the existence of the shared lane on the opposite side would make it more difficult for the EB permitted left drivers to ascertain their gap when figuring out exactly what the other driver is doing in the WB shared lane. This could decrease efficiency.

The WB direction wouldn't make sense to have permitted lefts with the shared lane. That would be a violation of driver expectancy by potentially stopping through vehicles in the shared lane. Yes, the situation exists on streets without dedicated turning lanes. However, the goal of using a shared lane (when a dedicated left lane already exists) is to increase the left turn throughput, which can really only happen if the shared lane has a protected left–left turn throughput decreases when drivers are waiting for a gap, then straight throughput decreases for vehicles stuck behind waiting left turning vehicles.

[Mdcastle]

Mn/DOT just handled it by using a doghouse and running split phase in the peak periods, flashing yellow arrow only in the non-peak.

[US 41]

People are too stupid to know you have to yield turning left on a green ball (yes, really). flashing yellow arrow emphasizes the need to yield.

What makes you think they will yield at a flashing yellow arrow if they are also blowing through solid greens?

[KEK Inc.]

People are too stupid to know you have to yield turning left on a green ball (yes, really). flashing yellow arrow emphasizes the need to yield.

What makes you think they will yield at a flashing yellow arrow if they are also blowing through solid greens?

I'll let you think about that for a second...

[wisvishr0]

All of this depends on the notion that people know what to do at a flashing yellow arrow in the first place. They're not logically consistent with anything (as I've argued several times), and often there's a blatant lack of signage. And it's not on many driver's manuals, like Maryland's or DC's. How the hell do I know what to do at one if I'm not a member of AA Roads? This is literally the ONLY place I'd heard of it, and when I encountered one in Iowa, I knew what to do because I'm an enthusiast.

Just to prove it, I asked my dad what he'd do, and he said "you'd go, because flashing yellow gives you the right of way."

My mom, though, said "you'd yield because you'd have to yield to all traffic at a normal flashing yellow." Yeah, no.

[cl94]

People are too stupid to know you have to yield turning left on a green ball (yes, really). flashing yellow arrow emphasizes the need to yield.

What makes you think they will yield at a flashing yellow arrow if they are also blowing through solid greens?

I'll let you think about that for a second...

The logic is that many people speed up when they see a yellow to try and make it through the light.

[KEK Inc.]

That's an apparent lack of logic.  The light goes red before the fya phase, ergo that mistake isn't really possible.


iPhone

[tradephoric]

The flashing red arrow (FRA) led to fewer fail-critical responses than a flashing yellow arrow (FYA), according to research cited in NCHRP Web-Only Document 123.   The following excerpts can be found on page 24 of the report: 

In the driving simulator a total of ten fail-critical (go) responses were observed at the two scenarios with FYA permissive indications. However, all but one of these responses occurred on the first observation of a FYA display by each driver.  Alternatively, no fail critical responses were observed at the FRA scenarios. These results were statistically significant.

At wide intersections where the left-turn lanes are separated from the through and right-turn lanes, and the left-turn driver cannot see the through movement indication, the FRA requires the driver to stop before proceeding significantly reducing left-turn capacity. 

Two simple questions.

1.   Which type of PPLT indication is safer (FYA or FRA)?
Based on the driving simulator results, drivers are more likely to yield to oncoming traffic at a FRA.  Drivers in the study were especially susceptible to experiencing a fail-critical (go) response when encountering a FYA display for the first time.

2.   Which type of PPLT indication is more efficient (FYA or FRA)?
In theory, drivers are required to come to a stop before proceeding at a FRA.  However, it's been well documented that the majority of Michigan drivers don't come to a complete stop when encountering a flashing red ball when it is clear to go.  If the FRA was introduced nationally, it's very likely drivers would treat the FRA the same way they treat the FYA and there would be no reduction in capacity.     

IMO, the flashing red arrow (FRA) would be safer than the flashing yellow arrow (FYA).  Also, the capacity of each would be the same. 

[vdeane]

2.   Which type of PPLT indication is more efficient (FYA or FRA)?
In theory, drivers are required to come to a stop before proceeding at a FRA.  However, it's been well documented that the majority of Michigan drivers don't come to a complete stop when encountering a flashing red ball when it is clear to go.  If the FRA was introduced nationally, it's very likely drivers would treat the FRA the same way they treat the FYA and there would be no reduction in capacity.     

IMO, the flashing red arrow (FRA) would be safer than the flashing yellow arrow (FYA).  Also, the capacity of each would be the same. 

Does that hold up if you were to station a very visible police presence at the intersection (especially if the stated objective was to catch people to don't follow the traffic light to the letter)?

[tradephoric]

Does that hold up if you were to station a very visible police presence at the intersection (especially if the stated objective was to catch people to don't follow the traffic light to the letter)?

Drivers would roll through the flashing red ball even if they knew a police officer was sitting at the corner looking for any traffic violations.  If a police department suddenly targeting drivers for rolling through the flashing red ball, the story would end up on the local news.