Thursday, June 23, 2011

Getting the green light: Valley ramp meters now more efficient



If you drive Valley freeways during rush hour, you’re probably pretty familiar with ramp meters …

They’re the two-light signals positioned at most Valley on-ramps that tell motorists when it’s okay to head onto the freeway.

Ramp meters have been used in the Phoenix-Metro area for about the past 20 years and maybe you think not much about them has changed … but, actually they’ve recently become much more efficient!

Thanks to a project funded through the Maricopa Association of Governments (MAG), roughly 300 ramp meters have been replaced with units that use newer, smarter technology.

As ADOT’s Intelligent Transportation System Supervisor Chuck McClatchey explains in the video above, the older ramp meters were not nearly as efficient as the new models.

“The new controllers actually operate totally independent of each other, which, means you can have 15 cars in one lane, no cars in the other lane and it will give 15 straight greens and just maintain red on the left side,” he said. “The older technology would give two greens and then a green to the non-existent cars. … So you can see that it really was not that efficient.”

But how does the ramp meter “know” a car is ready and waiting to take off onto the freeway?

Well, there are actually sensors in the ground adjacent to the signals that can detect a car as it pulls up. The ramp meter will then give a green light and start metering back and forth between the two lanes.

The meters also get information from the mainline, or freeway.

If the mainline is free-flowing, then the ramp meter will put on as many cars as possible. But if the mainline traffic slows down, the sensors pick that up and the rate at which cars are given a green light slows down some to help relieve the congestion.

The system has something called a queue-loop located at the very top of the ramp, too. The queue-loop is kind of a manual override that senses when traffic is backed up on the ramp completely up to the top. If that happens, the loop is activated and the metering goes to the fastest rate until the ramp is cleared. Basically, it’s a safety factor that keeps traffic from backing up into the surface street intersections.

All these features add up and help make it a little easier for motorists to get where they need to go!

24 comments:

  1. It would be helpful if it could see that no cars are in line to enter the freeway and keep the lights green. South bound 101 entrance at McDonald in Scottsdale never has a backup but it's metered.

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  2. I'm on a motorcycle and these lights never turn green for me. I end up taking my "turn" by blowing the red light.

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  3. Unknown:
    Thanks for letting us know about this.
    I just spoke with our ITS Supervisor, who said he could send a technician out to look at the ramp where you’re experiencing this issue. Would you let me know the location?

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  4. Inflatable water slide rental in Phoenix:
    Thanks for the comment! But, having a continuous green light, even when there is no traffic on the ramp, could create a potential safety issue.
    For example, if a group of three or four motorists see a green light on the ramp meter, they will assume they do not need to stop. But, as soon as the first car reaches the detection, the meter will kick into action and a red light will show.
    Now the cars are traveling at speed and once one car attempts to stop for the red light, it could set up the possibility for a crash. That’s why our ramp meters “rest in red,” and not in green.
    I hope this helps explain our meter operation!

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  5. People are just blowing thru the light as if they didnt exist. You should monitor streets with light activity and reset the hours it meters traffic.

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  6. Is there any evidence to indicate these "meters" have actually improved freeway safety?

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  7. Some of these new meters have what appear to be cameras above them. Are they photo radar cameras? I thought those were all taken down last year 2010? If they are photo radar cameras, are tickets being issued to violators, or are they simply being tested?

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  8. Anonymous (Sept. 21), thanks for the comment.
    There are many studies available online to support the benefit of ramp meters. Basically, ramp meters help to increase freeway speeds, decrease travel times and reduce delays. Ramp meters have also been shown to increase freeway capacity and reduce crashes (specifically rear-end collisions).
    This explanation is given in the U.S. Department of Transportation’s Federal Highway Administration Ramp Management and Control Handbook:
    “The manner in which safety is improved depends on the type of ramp management strategy selected. Ramp metering improves safety by breaking up platoons of vehicles entering the freeway, thereby allowing more orderly and safe interactions between merging vehicles and freeway mainline vehicles.” Hope this helps!

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  9. What does transportation law require the driver to do if they pull towards the signal and the ramp meter light turns green before they stop? Can you just proceed without stopping?

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  10. Hi Bob,

    Great question! Ramp meters should be followed like any other traffic signal. If you reach the light when it turns green, you can proceed without stopping if it is safe to do so.

    But always be prepared to stop when ramp meters are active and remember that only one car can go per green light.

    Hope that helps and thanks for reading the blog!

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  11. Anonymous (Oct. 14): We haven’t forgotten about your question!

    I passed your question to ADOT’s Intelligent Transportation Systems maintenance manager. He said that we don’t have any cameras at our ADOT ramp meter locations and what you may be seeing is the receiver for wireless detection.

    I’m working on getting a more detailed answer for you, but just wanted to pass along this information ... stay tuned!

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  12. We live in the White Mountains and came to Phoenix for a doctor appointment Wednesday. Coming back home this morning (Thursday) at about 6:40 AM I was trying to get on 101N at Southern. There were two lanes on the on-ramp and I was in the left one. I stopped for the red and waited while the right lane went green twice - looked in the mirror to see if I could get over to the right when my lane went green. By the time I stepped on the gas it went red again and I saw a flash. Am I going to get a ticket?

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    Replies
    1. Hi David,

      As you can see from the comments above, ADOT has no cameras at any of its ramp meter locations -- receivers for wireless detection are sometimes mistaken for cameras, though.

      However, that wouldn't explain a flash, so I'll pass your comment on to our electrical operations engineer and see what I can find out for you.

      Thank you!

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    2. Hi David,
      I just heard back from our electrical operations team and was told there are no components on the ADOT ramp meters that would cause any sort of a flash.

      Our only guess is that maybe what you saw was a reflection of the early-morning sun.

      Hope this helps!

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  13. Hey David, let me know what you find out, I had something similar happen to me, at the 101N and Broadway.

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    1. Good afternoon,

      ADOT has no cameras on any of its ramp meters and I was just told by our electrical operations team that there are no components that would cause any sort of flash either...

      Not quite sure what you or David might have seen, but our best guess is that maybe it was a reflection of some sort.

      Hope this helps!

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  14. What is the law in this matter. If you drive at the red light at 35 to 40 I always turns green. I see drivers do this all the time so is that running a red light even though it turns green the instant you approach the line?

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    Replies
    1. Good morning,
      Drivers should always be prepared to stop when ramp meters are active.

      However, ramp meters are to be followed just like any other traffic signal. If you reach the light when it turns green, you can proceed if it is safe to do so.

      Thanks for reading and I hope this answers your question!

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  15. Good morning,

    Last night as we were travelling on the I-10 eastbound exit on Warner I realized I accidentally ran a ramp meter. The flash after I passed it was what clued me in to what happened. I don't know what else the flash could have been but a camera. I was not familiar with this area as we were travelling to a concert venue and had gotten lost. I did try to slow down as I realized there was a ramp meter, but it was too late. I'm very upset because I pride myself on my perfect driving record, accident free and ticket free since 2003. Are you sure there are no cameras on these ramp meters, because I have to tell you it ruined my whole night at the concert worrying about it.

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    Replies
    1. Good morning,
      There are no cameras on the ADOT ramp meters and I've been told by our electrical operations team that there are no components on the ADOT ramp meters that would cause any sort of flash.

      I'm not sure where the flash you saw originated from (maybe it was a reflection or someone's headlights?), but you can rest assured it was not the ADOT ramp meter.

      Hope this helps!

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    2. Thank you so much! That does make me feel a lot better. I can't tell you how awful I felt that whole night.

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    3. Whats the big deal? If no one is at the light or beside you just run the light. It's purpose is to space, or meter traffic flow, so if there is no traffic just proceed through. I see so many people slam on the brakes to stop just to accelerate 1second later when the ramp is empty, its stupid and could be dangerous. Maybe they should just have alternating green lights so people are not confused.

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    4. Yes! This makes sense....but someone PLEASE answer the question "Is it legal/illegal to run these lights?"

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    5. It is illegal to run a red light on a ramp meter, just as it is against the law to run any red light. Ramp meters are to be followed just like any other traffic signal.

      Drivers who fail to obey the ramp meter signal can be cited (the violation falls under Arizona State Statutes 28-645 and 28-644).

      Ticket fines vary from county to county, but can typically range $140-180 and include points against your driving record.

      Delete

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