[Exaday]

Originally Posted by Troubleshooter

This is not the reason the flashing yellow arrow was created. Turn on circular green causes a hazard known as "yellow trap" if the circular green facing one direction ends earlier than the circular green facing the opposite direction. It is unsafe to end a permissive turn at that time, but that is exactly what the circular green left turn does.

Flashing yellow arrows cure yellow trap. The timing of the flashing yellow arrow is always the timing of the oncom8ing circular green, not the timing of the circular green facing the left turning driver. Thus, the flashing yellow arrow can still be flashing while the circular signals facing the same way are red.

Usually drivers who run a flashing yellow arrow think it is a steady yellow arrow ending the green arrow. Most if these drivers are from places where flashing yellow arrows have not yet been in use.

But the sign is quite informative.

We gain several benefits from the flashing yellow arrows:

1. Left turns can be made during a larger portion of the cycle, saving gasoline.

2. Left turn modes can be freely changed between exclusively protected, protected/permissive, and exclusively permissive, depending on either time of day or traffic levels.

3. Left turn sequences can be switched around at will without causing yellow trap. Possible sequences are dual lead, dual lag, and lead-lag.

4. The availability of lead-lag with permissive turns allows progressed green lights in BOTH DIRECTIONS on more two-way streets.

5. Progressed green lights means fewer stops, saving gasoline.

Good post!

I like the flashing lights myself. I thought there was more of a problem of people not knowing they could turn when that thing flashes rather than blowing through the light. Though I have no idea. I like them.

[DenverBrian]

These are all over Denver as well these days. I find them quite fine, although I wonder if a flashing green arrow might be better than a flashing yellow arrow. (Don't they use flashing green lights in Canada for this stuff?)

[ischyros]

Originally Posted by NLVgal

What was wrong with the left turn arrow followed by yellow arrow, red arrow, then the solid green with the signs that read "left turn yield on solid green"?

It was the same thing, but with less confusion. Your mileage may vary of course, but a yellow arrow means "hurry up and turn left before the light changes" to most valley drivers. We can only hope that they notice that it's flashing, I guess.

I agree. I'm not sure what the problem with these is?


We have a lot of them here in Indianapolis. When I see a yellow left turn arrow, to me it says oncoming traffic still has a red light. I think that's where the confusion is. If it's the solid yellow, I know that oncoming traffic has a green light. Of course you can get used to it if you're around it for a while. The city I work in is the roundabout capital of the US, but we're completely used to them. Other people come to town and completely freak out with them. But what is the problem with the above light? Why did it have to be changed?

[Tek_Freek]

They implemented them here last year. First time I saw one I had no idea what was going on. Luckily there was traffic coming the other way so I couldn't turn and I had time to read the sign.

I've decided I like them, but I'm not sure they're all that much better than yield on green.

[Troubleshooter]

Originally Posted by DenverBrian

These are all over Denver as well these days. I find them quite fine, although I wonder if a flashing green arrow might be better than a flashing yellow arrow. (Don't they use flashing green lights in Canada for this stuff?)

They ruled out using the flashing green arrow for this purpose because it means a protected turn in Canada. Our use for permissive turns would have caused accidents when Canadian or UK drivers saw them.

The steady green arrow means a required turn in Canada. All traffic seeing a steady green arrow must turn in the direction of the arrow.

They studied several different indications for permissive left turns before settling on the flashing yellow arrow:

- louvered circular green (Dallas phasing)
- flashing green arrow
- flashing yellow arrow (used in suburban Chicago IL and Reno NV)
- flashing circular yellow (Seattle WA)
- flashing red arrow (DE and MD)
- flashing circular red (MD and MI)

The flashing yellow arrow was chosen because it gave the most intuitive response, and because in most states, it already had the correct definition.

[Troubleshooter]

Originally Posted by ischyros

I agree. I'm not sure what the problem with these is?

We have a lot of them here in Indianapolis. When I see a yellow left turn arrow, to me it says oncoming traffic still has a red light. I think that's where the confusion is. If it's the solid yellow, I know that oncoming traffic has a green light. Of course you can get used to it if you're around it for a while. The city I work in is the roundabout capital of the US, but we're completely used to them. Other people come to town and completely freak out with them. But what is the problem with the above light? Why did it have to be changed?

The problem is yellow trap. It happens when the circular green changes to yellow for one direction on a street, but remains green facing the other way. A left turning driver seeing the yellow thinks both signals turned at the same time, and turns across live traffic. I have seen too many accidents caused by yellow trap.

The flashing yellow arrow prevents yellow trap when used properly.

The 5-lamp "doghouse" shared signal you show (and its inline counterpart) are still allowed, but have new regulations on them:

- The circular green may not be placed over or in front of a left turn lane in new installations. Shared circular/arrow signals must be over the closest thru lane or the lane line between the thru and the left turn lane.

- The shared circular/arrow signal must not cause yellow trap. It must be prevented though changes in the signal sequence or warned with a sign.

- If a shared thru and left lane exists, a circular yellow or red may not be shown with a left green arrow, and a left red arrow may not be shown with a circular green.

Yellow trap is caused by the following:

1. Use of a lagging left turn phase (The left turn has a green after the oncoming thru movement): Oncoming left turns are cut off with a yellow, while traffic the left turn turns across still has a green.

2. Phase skip with leading left turns (left turn goes before oncoming thru): At night, when there is no traffic on the cross street, the signal skips the cross street and causes yellow trap when the signal services a left turn signal.

3. The signal is pre-empted for a railroad crossing, a drawbridge, or an emergency vehicle.

[Troubleshooter]

Originally Posted by Tek_Freek

They implemented them here last year. First time I saw one I had no idea what was going on. Luckily there was traffic coming the other way so I couldn't turn and I had time to read the sign.

I've decided I like them, but I'm not sure they're all that much better than yield on green.

To the left turning driver, the flashing yellow arrow and the circular green have the same meaning.

The big difference is the indication given to traffic that is NOT turning left.

An indication is needed that releases a permissive turn without releasing traffic moving straight ahead. The flashing yellow arrow fills this need.

Flashing yellow arrow prevents yellow trap by allowing permissive turns to continue after the circular indications turn yellow and red, until the oncoming green turns yellow.

[MAXIALE02]

I didn't read all the posts, but whats up with the express lanes on the 15 freeway near the strip. I've seen single car drivers utilizing these lanes. Does anyone know the rule for these lanes?

[DenverBrian]

Originally Posted by MAXIALE02

I didn't read all the posts, but whats up with the express lanes on the 15 freeway near the strip. I've seen single car drivers utilizing these lanes. Does anyone know the rule for these lanes?

I think the rule is: Drive in 'em if you want. Those aren't HOV or diamond lanes; they're just bypass lanes for thru traffic. Not really much different than the far left lanes of any freeway.

[ischyros]

Originally Posted by Troubleshooter

The problem is yellow trap. It happens when the circular green changes to yellow for one direction on a street, but remains green facing the other way. A left turning driver seeing the yellow thinks both signals turned at the same time, and turns across live traffic. I have seen too many accidents caused by yellow trap.

The flashing yellow arrow prevents yellow trap when used properly.

The 5-lamp "doghouse" shared signal you show (and its inline counterpart) are still allowed, but have new regulations on them:

- The circular green may not be placed over or in front of a left turn lane in new installations. Shared circular/arrow signals must be over the closest thru lane or the lane line between the thru and the left turn lane.

- The shared circular/arrow signal must not cause yellow trap. It must be prevented though changes in the signal sequence or warned with a sign.

- If a shared thru and left lane exists, a circular yellow or red may not be shown with a left green arrow, and a left red arrow may not be shown with a circular green.

Yellow trap is caused by the following:

1. Use of a lagging left turn phase (The left turn has a green after the oncoming thru movement): Oncoming left turns are cut off with a yellow, while traffic the left turn turns across still has a green.

2. Phase skip with leading left turns (left turn goes before oncoming thru): At night, when there is no traffic on the cross street, the signal skips the cross street and causes yellow trap when the signal services a left turn signal.

3. The signal is pre-empted for a railroad crossing, a drawbridge, or an emergency vehicle.

Thanks for explaining but I don't know that I'll ever understand. lol It seems the flashing yellow would cause the same problems that the light I showed would. Maybe if I ever encounter it in person, I'll understand more the problems it solves that the doghouse one doesn't. Kind of like people who never have to drive roundabouts seem to hate them when first encountered, but when you live with tons of them, you start to love them.