Flashing yellow arrows

Maintenance/Repairs
21

One problem is that, with yellow trap, the southbound green is not next. It may have been skipped because no traffic was waiting to use it. You would have to be clairvoyant to know what color the opposing straight ahead light is. You can’t tell whether or not the yellow trap has happened by looking at your signal.

Another problem is the law saying, “The driver must be out of the intersection by the time the light turns red.” This makes it illegal to wait until the opposing traffic gets a yellow and red.

With the normal quad lead signal (4 five-section left turn faces, and the left turns go before the opposing straight ahead greens), yellow trap does not occur when traffic is heavy. It happens at night or on weekends, when traffic is light.

If no cars are waiting on one street, the signal skips those movements. This can then bring up the yellow trap scenario: One approach’s circular green changes to yellow, while the other direction’s signal stays green and also gets a green turn arrow. A car approaching the yellow with the intent to turn left is trapped. His light turns yellow and red, and if he entered the intersection to wait for a gap, he is now required by law to exit the intersection. But he can’t, because opposing traffic still has a green.

22

You will see it soon. It is scheduled to become the standard left turn signal for signals with left turn lanes, replacing the 5-section “doghouse” signal face.

Another advantage of the new face is that it can safely change left turn modes under time-of-day or computer control:

Automatic selection of left turn control type:

  • Exclusively protected (left turns must be made on green arrow)
  • Protected-permissive (left turns on green arrow, or use gaps on flashing yellow)
  • Exclusively permissive (all left turns through gaps on flashing yellow)

Automatic selection of left turn sequence:

  • Leading (left turn goes before opposing straight ahead)
  • Lagging (left turn goes after opposing straight ahead)
  • Lead-lag (one left turn goes before, the opposing left turn goes after)
  • Separated phases (the two approaches go at separate times)
  • None (Exclusively permissive mode)

These allow the signal systems to become more efficient, saving energy.

23

The problem is that you can’t witness the trap from the driver’s seat and realize that it is happening, because it can’t be seen. You can’t tell the trap occurred by looking at your own signal.

Here is how to possibly recognize a trap situation:

  • A left turning car suddenly cuts across in front of you as you are going straight ahead with a green light.

  • Your light turns yellow as you are waiting to turn left, but cars keep coming from the opposing direction. You think they are running red lights.

  • As you approach the intersection with a circular green, the green left turn arrow suddenly comes on.

But these things can also happen without a yellow trap, if drivers disobey the signal, or at T intersections or one-way streets.

  • Federal standards now require the yellow trap to be prevented or warned with a sign “ONCOMING TRAFFIC MAY HAVE EXTENDED GREEN.” But most state and local governments have not complied. Many engineers do not realize that it can happen if the signal skips the green for the side street, and many city councils won’t approve the funds for the required signs.

  • The solution of always using a leading left turn arrow also precludes the green wave (lights turning green as traffic comes to them) on many streets. The left turn arrow must lag at some intersections to make the green wave progression possible. The only ways to do this safely are either to use an exclusively protected 3-arrow face (requiring a red arrow when the opposing signals are green), or to use the flashing yellow arrow face on both approaches (flashing yellow when opposing signals are green). Using turns on a circular green is not safe - it causes yellow trap.

24

Driver training doesn’t help here, because you can’t recognize that yellow trap is occurring until it is too late to prevent the accident.

25

Until recently, Texas has been using a different system called Dallas Phasing. In that system, the left turn signal retains a circular green while the adjacent straight ahead signals change to yellow and red. But that circular green has louvers, so the straight ahead traffic can’t see it.

The problem with the Dallas display is that it can’t be used without a rigid mounting on a mast arm. On a span wire, the wind makes the signal sway, and shows the circular green to other traffic. Dallas phasing also does not work on curved roads.

I just read today that Texas, Virginia, Maryland, the Netherlands, and South Africa have started using Flashing Yellow Arrows too. It’s the left turn signal fo the future.

26

The problem with red light cameras is that jurisdictions using them are then shortening the yellow to collect more revenue. This should be thrown out by courts, because government uses its greed to cause accidents, and because the defendant has no way to cross-examine the camera (the only witness against him).

Question: Are those people intentionally running red lights, are the yellow lights set too short by revenue-hungry officials, or are the drivers being fooled by yellow trap?

27

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Texas has also started using cameras to catch red light runners. I wish they would do that in all 50 states.

Oh the revenue they could collect here in NH and MA. THOUSANDS A DAY. I see EVERY SINGLE DAY at almost every light I travel through. I’ve been rear-ended twice living in NH. Both were when I was stopping for a light that was yellow and turned red as I stopped…the car behind me was trying to rush through the red-light.

28

Are those people intentionally running red lights, are the yellow lights set too short by revenue-hungry officials, or are the drivers being fooled by yellow trap?

I don’t have a problem with someone who enters the intersection while the light is yellow or just barely misses the yellow. After all, there is usually a delay before the green light comes on for the cross traffic and it can be an honest mistake. I have a problem with people who run the light after it has turned red before they even got to the intersection. They do this just because they don’t want to wait and the car in front of them ran the light. If the camera had a one second delay before it activates, that would be fine with me.

Where I live (Jacksonville, FL), law enforcement is a joke. Per capita, we have the highest murder rate in Florida. You can drive like a complete idiot and your odds of getting a ticket are about the same as being struck by lightening. My belief is that installing red light cameras would be a good start to restoring law and order on the roads and they would make the roads safer. This is a conservative town with a “damn the law” attitude. If you see someone throwing a milkshake out a car window or dumping out an ashtray on the ground at a red light, you can bet he or she is a Jacksonville native. The natives here treat this town like a toilet. I am beginning to think that if I want to live where the roads are safe and the streets are not strewn with garbage, I will have to move.

Sorry for the rant, but it helps to get it off my chest.

29

But whether the yellow trap is happening or not, drivers are trained not to pull out if oncoming traffic isn’t clear or hasn’t stopped. If all drivers didn’t ignore that advice and they were required to take a basic driver’s education class, this wouldn’t be an issue.

You are proposing a solution to a problem that wouldn’t be a problem if people did what they should be going…yielding to oncoming traffic unless there is a green arrow. The problem is that drivers don’t seem to know the difference between a solid yellow light and a yellow arrow. So instead of raising the educational bar, we look for a systemic solution that allows us to lower the bar. This is a systemic solution to an educational problem. It is no wonder our educational system is such a mess if we apply the same reasoning.

I would not call this an “accident.” There is nothing accidental about choosing not to yield to oncoming traffic, which is what you are supposed to do with a solid yellow light.

30

“Also, the majority of these signals are synchronized with the signals in the opposite directions, and the ones that are not synchronized can solve this problem by having all the lights in both directions turn yellow and red at the same time.”

This is what I was referring to when I said you were wrong. It is not that simple. There are several reasons why this is not done:

  1. The agency doesn’t know it is happening, because it usually happens late at night, when one street is completely empty of approaching cars. At that time, the signal skips all of the cross street greens. The agency always inspects the signal in the day, when the employees are at work to do the inspections. It takes special equipment and programming to eliminate this sequence.

  2. The agency does not want to restrict left turns to just the time when the green arrow is on. This reduces the overall capacity of the intersection.

  3. The agency thinks the progression of green lights from intersection to intersection is important in reducing energy use, since each stop a car makes uses up energy (trucks use up even more each time they stop). But it is often impossible to achieve progression on two-way streets without using lagging left turn signals (the green arrow comes on after the opposing straight) on some approaches.

They don’t want to stop all left turns with red arrows when both circular greens are on, but allowing turns on the circular green causes yellow trap with a lagging left turn. The flashing yellow arrow and the Dallas display (see below) are the only ways to use a lagging left turn safely.

  1. The flashing yellow arrow might be needed to prevent yellow trap at an intersection that has a green arrow for one left turn, but not for the other left turn. It is the left turn without the green arrow that is trapped in this case.

  2. Signals with preemption for emergency vehicles also cause yellow trap if a left-turning car facing the emergency vehicle gets a yellow and red, so the emergency vehicle can have an exclusive green. That car will turn left in front of other traffic if the emergency vehicle is far away, especially if the signal never yellow traps at any other time.

This is not a matter of opinion, but fact.

The flashing yellow arrow is used because an indication is needed to continue to allow turns across opposing traffic WHILE AT THE SAME TIME STOPPING THE STRAIGHT AHEAD TRAFFIC ON THAT APPROACH. A circular green can’t do the job, because it also lets straight ahead traffic go.

The indication needed is one that lets left turns turn through gaps, while stopping straight ahead traffic. Until the flashing yellow arrow was redefined, there was no such indication available.

31

Why does everyone think that it is good for government to have more revenue? More revenue for government means less for the economy. Most government projects do not expand the economy, because they do not produce productive products for sale on the market.

32

That is not really the problem. The problem is that the engineers need to be able to end the permissive left turn through gaps in traffic at a DIFFERENT TIME in the signal cycle. This can not happen if the same signal display (circular green) is used for both.

The real problem is that the circular green has too many meanings for too many drivers doing different things:

  • For straight-ahead traffic, it means go, but left turns might turn through gaps in your stream.

  • For right-turn traffic, it means go, but left turns might turn through gaps in your stream, and you must yield to pedestrians in the crosswalk.

  • For left-turn traffic, it means you may turn through gaps in opposing traffic (straight and right turn), and you must yield to pedestrians in the crosswalk.

When the flashing yellow arrow is used, it takes away the meaning of the circular green for controlling left turn traffic at that intersection. Now the circular green and the flashing yellow arrow can be ended at different times in the signal cycle. This makes the intersection a lot safer, and makes many more solutions available to the traffic engineer.

It would be nice if all drivers waited behind the stop line until they can turn through gaps in opposing traffic. I do this. The problem is that many intersections are so overloaded that they only way to make your left turn is to wait in the intersection, and turn when the light goes yellow. If you wait at the stop bar, you don’t get to go at all, and you might have to wait several cycles to make your turn.

This is caused by not enough money in the street department to fix such overloads (the legislators would rather spend the money on wasteful arts and sports).

I have a trick for avoiding having to do that, but it works only if you are in a city with blocks. I drive beyond the intersection going straight, and then make three right turns. But it doesn’t work at isolated intersections, or intersections where neighborhoods are designed to keep out other traffic, and in a strange city, you don’t know whether or not the needed connections are there.

I just realized that the use of circular green for permissive left turn causes another strange event:

In the original “quad” left turn cycle, the signals had separate faces for left turns, with “left turn signal” signs over the signals. Left turns were stopped by red lights, and not permitted on circular green. The signal controllers have two timing units (called “rings”, since each services a rotating ring of signal faces). The timing units are arranged like this:

Ring 1:
Phase 1 - southbound left
Phase 2 - northbound straight

Phase 3 - westbound left
Phase 4 - eastbound straight

Ring 2:
Phase 5 - northbound left
Phase 6 - southbound straight

Phase 7 - eastbound left
Phase 8 - westbound straight

Since only one phase (movement) in each ring can go at any one time, each timer has only one movement to deal with at any one time. This is why the left turns do not have to end at the same time. Each traffic movement’s timing is always controlled by one ring.

The ----- in each ring is the barrier. Both rings must be on the same side of the barrier (above it, or below it) at the same time, and they must cross the barrier together. The timing normally moves down the list in each ring, but if no phases have vehicles waiting on the other side of the barrier, the ring can back up and return to an earlier phase on the same side.

But when the 5-section permissive left signal face is used, an unexpected thing happens. The timing for left turns passes back and forth from ring to ring, because the circular green seen by the left turning driver is controlled by the other ring:

Ring 1:
Phase 1 - southbound left
Phase 2 - northbound straight and northbound permissive left

Phase 3 - westbound left
Phase 4 - eastbound straight and eastbound permissive left

Ring 2:
Phase 5 - northbound left
Phase 6 - southbound straight and southbound permissive left

Phase 7 - eastbound left
Phase 8 - westbound straight and westbound permissive left

This intertangles the timings for the left turns, and causes the yellow trap by ending the permissive left turn at the WRONG TIME. If one side of the barrier has no cars waiting, the backing up of a timing ring can cause yellow trap.

With flashing yellow arrows, control of each left turn is always confined to the same ring:

Ring 1:
Phase 1 - southbound left
Phase 2 - northbound straight and southbound flashing yellow left

Phase 3 - westbound left
Phase 4 - eastbound straight and westbound flashing yellow left

Ring 2:
Phase 5 - northbound left
Phase 6 - southbound straight and northbound flashing yellow left

Phase 7 - eastbound left
Phase 8 - westbound straight and eastbound flashing yellow left

Yellow trap is not possible here, because the timings are controlled to always eliminate the unexpected conflict. It does not matter if a ring decides to back up to an earlier phase.

33

Why does everyone think that it is good for government to have more revenue?

Because the economy isn’t our only consideration. We have a moral imperative to lower infant mortality, improve our underfunded schools, and ensure children don’t starve.

I guess some people care more about the economy than these things, but not me.

34

That is not really the problem. The problem is that the engineers need to be able to end the permissive left turn through gaps in traffic at a DIFFERENT TIME in the signal cycle.

Is that really the problem? From where I sit, engineers don’t “need” to do that. They have increased flow capacity by sacrificing safety. A good engineer would find other ways to increase capacity that don’t put people in danger.

There is more than one way to solve the problem of insufficient capacity, and if we don’t take the lazy way out, we avoid this problem all together. Instead of fiddling with the programming of the lights, we can increase capacity in a way that doesn’t compromise safety. We can do things like build overpasses or cloverleaf intersections to reduce or eliminate the use of traffic signals and the need to turn left across traffic. We can build more lanes. We can provide useful and well-designed mass transit to relieve congestion on our roads.

Programming the lights in a way that creates this “yellow trap” hazard is a half-a##ed way to address the problem of congested roads in the first place.

If we can agree to disagree, I will acknowledge that the flashing yellow arrow will solve the problem. We don’t have to agree on which idea is the best solution and we don’t need to agree on what led to this problem in the first place. Of course, not everyone will know what a flashing yellow arrow means. There will be a learning curve. I hope nobody dies in the process.

35

That’s called “digital communications”.

36

Has it occurred to anybody that if the blinking yellow left arrow with solid red light is so confusing that WE are struggling with it, the newbie, the elderly, and even the average driver who’s not as interested as we are is going to really struggle with this.

This concept must have been designed by a committee. It sounds to me like an accident producing design. Like an attempt to please ALL the committee members.

37

Is that really the problem? From where I sit, engineers don’t “need” to do that. They have increased flow capacity by sacrificing safety. A good engineer would find other ways to increase capacity that don’t put people in danger.

There is more than one way to solve the problem of insufficient capacity, and if we don’t take the lazy way out, we avoid this problem all together. Instead of fiddling with the programming of the lights, we can increase capacity in a way that doesn’t compromise safety. We can do things like build overpasses or cloverleaf intersections to reduce or eliminate the use of traffic signals and the need to turn left across traffic. We can build more lanes.

These cost hundreds of times more than modifications to traffic signals do.

We can provide useful and well-designed mass transit to relieve congestion on our roads.

What in the world is that? Except in the 15 largest cities in the US, mass-transit rarely services more than 10 percent of the trips. This is simply because the mass transit does not serve one end of the desired trip in the other 90 percent of the cases.

Programming the lights in a way that creates this “yellow trap” hazard is a half-a##ed way to address the problem of congested roads in the first place.

That’s why we need the flashing yellow arrow. It removes the yellow trap, by allowing the traffic signal to end the permissive left turn at the correct time in the signal cycle. Using the circular green forces the permissive turn to end at the WRONG time, creating yellow trap.

It is the use of the circular green as a permissive turn indication that forces the signal to end the permissive turn at the WRONG TIME. The new indication removes this limitation, by SEPARATING the end of the permissive turn from the end of the straight ahead flow with different signal indications.

Of course, not everyone will know what a flashing yellow arrow means. There will be a learning curve. I hope nobody dies in the process.

That’s the amazing thing. Most people pick it up the first time they see it, especially if they see the light changing through the following sequence:

green arrow
yellow arrow (4 second clearance)
red arrow (2 second red clearance)
flashing yellow arrow

It’s almost the same sequence you see with the 5-section doghouse signal, but with the flashing yellow arrow substituted for the green ball. Some jurisdictions retained the doghouse arrangement, and replaced the circular green lens with the flashing yellow arrow (but they changed the wiring and programming for safety).

One city has a “LEFT TURN YIELD ON FLASHING <-” sign, but the others report that most drivers get it without the sign. The ones that don’t usually stop and figure it out.

Another advantage is that, when a green turn arrow ends before the opposing green turn arrow ends, the flashing yellow arrow can start immediately (since it is tied to the opposing circular green, not the adjacent circular green). The circular green used for a permissive turn must wait until the opposing green turn arrow ends, because it must wait for the straight ahead circular green to be permitted.

Google “flashing yellow arrows” and you will find a wealth of brochures on the subject.

Also check out an animation of flashing yellow arrows, showing the signals seen in both directions, here:

38

Has it occurred to anybody that if the blinking yellow left arrow with solid red light is so confusing that WE are struggling with it, the newbie, the elderly, and even the average driver who’s not as interested as we are is going to really struggle with this.

It is more confusing in print than it is in reality. The flashing yellow arrow and the solid red are on different signal faces. The flashing yellow arrow is on a dedicated left turn face. The circular red is on the two faces for straight-ahead traffic.

Here is an actual installation. Play it twice, because it leaves out the first few seconds the first time:

39

I agree, this looks like garbage constructed by people who probably don’t drive that much themselves. How many people do you know who can’t understand a yield sign let alone this.

Do people really just jump out into moving traffic when the light turns yellow and oncoming traffic is not slowing down? Really, this is a training issue. The person making the left turn should be looking at the oncoming traffic, there are plenty of people who drive strait through the yellow, it is not just for people turning left, it doesn’t matter to them if the light is green or yellow.

Any extra time staring at additional light changes is less time you are looking at the road.

Edit: for this all inclusive junk. It is not even linear with the lights, the lights don’t go from bottom to top, but up, down, up again. Try to explain that to the color blind drivers.

Maybe we should just put a disco globe up there.

40

Thanks for the link TShooter.
Having seen it, what’s the point? Cars with a full green still cannot legally usurp the right of way of an oncoming vehicle to make a left hand turn in front of him. The oncoming car has the right of way anyway.

Definitely the results of a commitee meeting IMHO.