Monday, March 10, 2008

The head-scratching flashing yellow

Got a few e-mails about this story on the new flashing yellow arrow, which replaces the "green ball" for permitted - but not protected - left turns. All asked: What about people who are color blind?

The new flashing yellow signal heads have four different signals - one for green arrow, yellow arrow, red arrow and flashing yellow arrow - so I assume you could still figure out what's going on by watching the which signal head is in use. But I don't think it will be easy. The pattern on the new lights can give you whiplash - green arrow, yellow arrow, red arrow, flashing yellow arrow, yellow arrow, red arrow.

What confuses me about the new signal is the second yellow arrow, which comes after the flashing yellow arrow. The flashing yellow arrow means you can make a left turn but you must yield. The second yellow arrow means that signal is ending.

When a lot of people see a yellow, they think they have one or two seconds to get through the intersection, and are protected in going straight or turning. That's not the case with the second yellow in this sequence.

Maybe the flashing yellow arrow should flash much faster before it turns to red?


Racer X said...

Or they could leave it like it is and require people to pass a driving test. Apparently they'll let anyone get a license if this is a real problem.

Its not that hard, the turn isn't protected unless you have an arrow. Period. Red means stop, whether its solid or an arrow. Period.

Anonymous said...

Steve --

I hashed all this out in column in 2004.

"But there would seem to be a problem with this new system. It is not obvious that a flashing yellow light is more permissive than a solid yellow light. Indeed, you might conclude that the flashing yellow connotes a greater sense of caution; it is flashing after all. Plus yellow lights do not traditionally convey any information to drivers about the status of oncoming traffic. Yellow traffic signals tell drivers that the signal is about to turn to red, nothing more."

There will be a horrific accident due to these signals. In addition, CDOT/NC DOT are fully on board with stripping out "green ball" unprotected turns at every opportunity. Several years ago, for example, they removed the "green ball" left from the intersection of Hwy. 51 and Fullwood Ln. near Matthews for no good reason, resulting in increased idling and emissions.

Genius at work.


rod said...

IMHO, the real problem is the solid yellow arrow. There should NEVER be a signal with two different meanings, which is what they have with the solid yellow arrow. A driver shouldn't have to know which signal preceeded the current one to know what it means.

This poor choice WILL result in a bad accident ... it's just a matter of time.

Anonymous said...

Having seen the description of this signal methodology, I don't like it at all. It's too confusing, even for someone like me who could give a short dissertation on traffic signal design and methodology. There's nothing wrong with the normal five-face protect signal and the sign that says "Left Turn Yield On [Green Ball]". It's been around longer than I-485, so best to leave the thing alone.

There is one improvement I would like to see brought to American roads, and that's the use of yellow in conjunction with red to signal the beginning of the green phase. On a TV show some time ago, I saw this in action on a British traffic signal. The light was red, then the yellow came on so that they were both on solid for about two or three seconds, then they dropped to green. It was pretty cool, almost like the Christmas Tree assembly they use in drag racing here.

Jonathan said...

Back in the late 1960's and early '70's, traffic lights in New York City would go this way:

Green light go,

Then green and yellow together for several seconds,

Red light would appear, and the green and yellow would go out.

Not so British, after all! And yes, it was a really neat view!

Anonymous said...

agree completely with racer x. just learn how to drive in the 1st place. if a green ball confuses ppl, this new concept will only be worse. if you can't understand that a green ball isn't a protected turn, you should have your license stripped.

Anonymous said...

I am an independent researcher and have done some research here in NC on the flashing yellow arrow. What I have found is it is difficult to explain what happens in words but actually driving through the signal is less confussing. I know of about 10 locations where the new left turn signal indication has been installed in NC and in 9 of those locations, each having a green ball prior to flashing yellow arrow, there was a reduction in crashes. I know it is easy to complain about something new and it is easy to fall back on the old "someone is going to get killed" statement but after people have had a chance to experience the new signal head they adapt quickly.

Anonymous said...

I just read this and i'm not if anyone is even reading this thread anymore, but these are my 2 cents. i think the reduction in accidents is not an honest measure for people's UNDERSTANDING of the new light pattern. if anything it showcases the confusion and caution that the light provokes. also the light at johnston and 485 is a horrible example of success, unless you're traveling that corridor at off-hours, you will seldom be forced to make a decision at that light with oncoming traffic at full speed. most of the time the traffic is so thick that folks are being cautious regardless of the light. with a more widespread implementation of this "fix", you will see more accidents when drivers are forced to make actual decisions based on the signal the light is providing. this coupled with I-485, NC-16 in south Charlotte, and many others is the perfect example of just how confused the NC DOT is. Amazing!

Troubleshooter said...

The problem with the circular green is not driver confusion. It is that the permissive left turn and the straight ahead flow must must sometimes be ended at different times in the traffic signal cycle. There is currently no display that can do this.

So they cut off the permissive turn too early because the straight ahead traffic must be stopped. This causes accidents when the opposing signal is still green.

Troubleshooter said...

We used to have red and yellow together before green. It caused accidents. It is now strictly prohibited by federal law.

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Troubleshooter said...

Google "flashing yellow arrows"

Anonymous said...

Now in July -- these blinking yellows are everywhere.

It's quite easy to explain, really, a flashing yellow is no different than the solid green ball with no left turn signal -- except now it's in the left turn lane where it doesn't belong making driving even more dangerous to those who have to turn left on major intersections.

They should really have installed a blinking yellow arrow under all lights in intersections that don't have left turn arrows or left turn lanes to remind the inexperienced or tired driver to use caution when turning left on a green ball -- that oncoming traffic doesn't stop. That can backfire too; however, since motorist might think the light is turning yellow and slow down for no reason.

The problem I had with this horrible system is that the blinking arrow went to a solid red arrow when I was in the middle of the intersection -- I used to be able to stop at the intersection when a solid yellow arrow showed up after the green arrow and never worried about being stuck in the middle with a red arrow -- I'd only go past the line on a green arrow. So I left tire marks when having to turn left on a red arrow when already way past the line -- so there's a potential accident there especially in major intersections.

The blinking yellow has turned a defined turn on green and stop on red to a green ball where you proceed with caution and if it turns red on you, then move or be stuck in the left turn lane with cars avoiding you.

Unless a blinking yellow is different than a green ball where you're not supposed to be in the middle of the intersection but stop at the line till all is clear -- however the problem with that is if it appears all clear and you start turning -- but then you have to then yield to a car -- well you're in the middle of the intersection aren't you....the light turns to a red arrow and you leave tire marks or risk being stuck out in the middle waiting to be creamed.

I just hope this doesn't cause drivers to think they have to back up really fast since the arrow turned red, causing accidents.

Over all, I feel a blinking yellow on the left turn signal is really really freakishly annoying and it drags all drivers' attention to it because it's blinking on the way left side and drivers then aren't looking at what's in front of them that one second and that can potentially cause more accidents.

Bottom line: The left turn lane is no longer safe and is no longer different than not having a left turn lane with a left arrow light.

Time will tell on that....

I believe that in a year's time they'll take the blinking arrows's too bad people may have to unnecessarily get injured or killed to cause this to happen. I sure hope I'm wrong.

Troubleshooter said...

To the left turning driver, there is no difference between circular green and the flashing yellow arrow.

The big difference is in the meaning for the drivers who are NOT turning left.

Circular green also lets other movements go. Flashing yellow arrow does not.

This difference can prevent a hazard called "yellow trap," allow more safe signal sequences, allow progressing green lights from intersection to intersection on more two-way streets, and save more gasoline.

Troubleshooter said...

There is a steady yellow arrow for several seconds after the flashing yellow arrow ends. The steady yellow arrow appears in a different signal lens. It can never change directly from flashing yellow arrow to steady red arrow.