Please register to participate in our discussions with 2 million other members - it's free and quick! Some forums can only be seen by registered members. After you create your account, you'll be able to customize options and access all our 15,000 new posts/day with fewer ads.
I disagree with the need for flashing yellow turn lights. Didn't we all have to pass a test to get a driver's license, where you learned green means "go, if it is safe to do so" ? The solid green has worked well for decades for me.
I also hate getting a solid red turn arrow when there is no traffic in sight. I would welcome a flashing yellow arrow in that case.
You miss the point.
The flashing yellow arrow and the circular green mean the same thing to the driver who is turning left.
But they have totally different meanings to drivers who are NOT turning left. This is the main difference.
The flashing yellow arrow was invented to fix a danger called "yellow trap". It occurs when all of the following are true:
- Left turns are allowed on the circular green in both directions on the same street.
- The signal is showing circular green in both directions on that street.
- The circular green facing one direction ends before the circular green in the other direction ends.
The left-turning driver receiving the early yellow does not realize that the oncoming signal is still green, and turns in front of oncoming traffic.
The flashing yellow arrow keeps the left turning driver waiting for gaps until the oncoming signal turns yellow. Then a steady yellow arrow ends the flashing yellow arrow.
If you're in a big hurry and need a light to change immediately, pick up something like some mail or a magazine to glance over, or try to accomplish something on your phone before the light turns green again. Works instantly for me!
Want to see how a municipality can royally screw up some traffic lights, take a few trips up and down Creedmoor Rd from 540 down to Millbrook. They have those lights synced now so that you get stopped at every light for the full duration. It's a lot like Capital Blvd from 440 to the 401 split used to be, but they eventually "fixed" that bottleneck by changing the syncing of the lights. Creedmoor has actually gotten worse. If I get stopped at Strickland, I find myself driving much faster than usual trying to get through the next light before it changes. Never works.
DO NOT read or use your phone while driving. Cell phone use is now a larger cause of traffic accidents than drunk driving.
It's rare to find synchronized traffic signals. Raleigh did some in a few areas such as part of Capital Blvd..
Traffic signal progression (what you call synchronization) is easy on isolated one-way streets or pairs of one-way streets, but very difficult on two-way streets and in grids of streets.
There is a new device that can make traffic signal progression easier. It is the flashing yellow arrow.
The flashing yellow arrow makes possible the lead-lag signal sequence with permissive turns. The lead-lag signal sequence has the green left turn arrow at the beginning of the time for the street for one direction, but at the end of the time for the street in the opposite direction. This allows the signal to operate where the progressed platoons of cars arrive at different times. Left turns on a circular green prevent the use of the lead-lag signal due to the yellow trap hazard.
The original reason the flashing yellow arrow was developed was to allow the lead-lag signal without forcing left turns to stop for red arrows during oncoming circular greens.
I think Cary has great traffic lights, I'm a huge fan of the sensors. I was recently out of town and felt like I spent half of my driving time sitting at red lights.
The only thing I don't like about the sensors is that sometimes they won't sense my car and I'm left languishing at a red light, waiting for another car to arrive and trip the sensor. I think it's because my car is a small, soft-top convertible. It makes me wonder if people on motorcycles have to deal with that a lot. But times like that make me wish that the lights had a backup program to change every few minutes and not only rely on sensors, since they don't always detect my car.
If you drive up beyond the end of the sensor, the signal assumes that you turned right on red, and forgets you were there. Usually they paint a stop line on the road so you stop in the right place. If you drive so your car is beyond the line, the detector can't see it. Stop with your front bumper behind the line. Stay there!
I have seen drivers diddle themselves out of a green light by creeping forward in impatience until they are off the detectors. Older detectors (1960s) used to react to motion of the car, but all of today's detect the presence of a vehicle.
I really don't like the yellow flashers. Can't see what makes them different than green lights. Unless people all think a green light (not a green arrow) means they have the right of way when making a left turn.
The difference is the indication given to drivers who are NOT turning left.
I'd rather it didn't flash at me. Cannot see the benefit of the flashing.
It was the only indication left without a conflicting meaning, and it already had that meaning. But it used to be allowed only when the signal was on night flash.
They researched the following indications:
- Flashing green arrow - dangerous for Canadians driving here (protected turn in Canada)
- Flashing circular yellow (used in Seattle) - confusing to drivers in other lanes*
- Flashing circular red (used in Michigan) - requires a stop for each car*
- Flashing red arrow (used in Delaware) - requires a stop for each car
- Flashing yellow arrow (as used in Reno Nevada) - no problems
- Flashing yellow arrow (as used in Chicago) - lack of steady yellow after green arrow caused problems*
- Steady yellow arrow - already has a conflicting meaning of clearing the intersection.
- Steady white arrow - already used for transit and light rail signals.
- Introducing a steady arrow of another color - could not be made safe for color-blind people.
* All instances have now been removed.
Last edited by Troubleshooter; 07-09-2013 at 11:16 PM..
I've heard of pressure plate sensors (i.e., weight) for traffic lights, but I don't think I've encountered one. Of course, the induction loops are quite common, and I sometimes also see the mounted proximity detectors.
Pressure plates are obsolete, because they require the signal controller to remember that they have been tripped. They also fail quite frequently. A loop detector or a television detector still sees the vehicle until it leaves the area, so the signal can then "forget" a lone car that turns right on red..
Occasionally I see pressure detectors mounted on a bridge where the steel girders keep the loop detector from working. A loop detector is a giant version of a handheld metal detector, and the bridge girders are metal.
I wonder if the Lotus like drive for adding "lightness" via aluminum and composites will get vehicles to the point where they don't trip the induction loops?
I trip a number of induction loop traffic lights in my early morning trips - it seems that they're now all set to force you to stop. What a waste of time and resources. Previously a number of them would only require a touch of the brakes and a 4-2 downshift ...
Frank
The use of detectors and signal progression are mutual enemies. Each undoes the benefits of the other.
The detector detects the absence of traffic and turns the signal red. Then the platoon comes from the other direction. But the signal can not change until it finishes dealing with traffic on the side road, so those cars have to stop. So you have to stop at each light.
Note that the sudden absence of traffic is really the event that brings up a yellow light when detectors are used. The light stays green until the street runs out of traffic, or a pretimed limit is reached. Then the signal advances to the next green light in the rotation that has cars waiting. Many signals have two timing units, so they can handle at the same time the timing of two different traffic movements that don't conflict with each other. Thus, the left turns in opposite directions can end at different times, each when it runs out of cars.
When signals are progressed, the timing of the beginning and end of the green is carefully planned to anticipate the arrival and end of the platoons of cars from the signals in each direction. The addition of detectors upsets this careful timing.
Signals with left turn arrows on both streets usually can not be progressed. The cycle length must be too long for effective progression.
With signal progression, detectors are usually used to measure traffic flow so a computer can select the best timing plan, not to make the individual signals more responsive.
Last edited by Troubleshooter; 07-09-2013 at 11:21 PM..
DO NOT read or use your phone while driving. Cell phone use is now a larger cause of traffic accidents than drunk driving.
I agree completely. But I see it every time I drive somewhere. My favorite is the car that speeds past you, going 10-15 over the limit, and two minutes later that car is going 10 under the limit, and everyone is swerving to get around them...and as I pass I see they are now engaged in a heated two-thumbed typing contest!
I can spot phone users, when I'm behind them, like my dog spots squirrels!
My suggestion about reading or using a phone, was purely tongue in cheek about passing the time while stopped at a light. And honestly, I'd prefer most people not do that either, as it requires me honking at them to get moving 12 seconds after our light has turned green!
The use of detectors and signal progression are mutual enemies. Each undoes the benefits of the other.
The detector detects the absence of traffic and turns the signal red. Then the platoon comes from the other direction. But the signal can not change until it finishes dealing with traffic on the side road, so those cars have to stop. So you have to stop at each light.
Note that the sudden absence of traffic is really the event that brings up a yellow light when detectors are used. The light stays green until the street runs out of traffic, or a pretimed limit is reached. Then the signal advances to the next green light in the rotation that has cars waiting. Many signals have two timing units, so they can handle at the same time the timing of two different traffic movements that don't conflict with each other. Thus, the left turns in opposite directions can end at different times, each when it runs out of cars.
When signals are progressed, the timing of the beginning and end of the green is carefully planned to anticipate the arrival and end of the platoons of cars from the signals in each direction. The addition of detectors upsets this careful timing.
Signals with left turn arrows on both streets usually can not be progressed. The cycle length must be too long for effective progression.
With signal progression, detectors are usually used to measure traffic flow so a computer can select the best timing plan, not to make the individual signals more responsive.
Unfortunately your response doesn't apply to my "early morning" trips. During this time, the traffic lights are set to default to red in one direction and (hopefully) green in the other. The detectors are used to trip the red signal green for the occasional traffic from that direction. After a brief time, the signal then reverts to red in the default mode. Many intersections in this area function this way in overnight mode. As long as the detection loop can be set to allow for early enough detection, the light should change without requiring a stop. I understand this isn't always possible ... but intersections where this worked previously appear to have been reset.
I agree fully that during regular traffic periods ... progression works best.
Frank
Please register to post and access all features of our very popular forum. It is free and quick. Over $68,000 in prizes has already been given out to active posters on our forum. Additional giveaways are planned.
Detailed information about all U.S. cities, counties, and zip codes on our site: City-data.com.
Please register to participate in our discussions with 2 million other members - it's free and quick! Some forums can only be seen by registered members. After you create your account, you'll be able to customize options and access all our 15,000 new posts/day with fewer ads.
