• Sep 23, 2010
Anyone who's sat at a red light for minutes on end in the middle of the night when there's no cross traffic can cheer on science for proving what we already knew: lights that adapt to the flow of traffic, instead of dictating the flow of traffic, can improve the flow of traffic. A team of researchers discovered that if you let lights locally decide how to time their signals based on how much traffic they're dealing with, and then communicate that with nearby lights, you get closer to the "green wave" of lights that keeps thing moving smoothly.

The issue with the centralized, top-down system of control is that it is geared to address an average traffic situation that rarely occurs as planned. The variations in rush hour traffic mean that lights are trying to apply one solution to a vast number of situations. In their trial in Dresden, Germany the team found that traffic congestion was eased by nine percent, pedestrian congestion by 36 percent, and bus and tram traffic by 56 percent. With rush hours spreading in time and distance, the proof and implementation of this can't come soon enough. Thanks for the tip, Toy!

[Source: Science News | Image: Corbis/Getty]


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  • 52 Comments
      • 4 Years Ago
      There's this one traffic light in my area that gives the right of way to the plaza at night. The traffic light is in between two major intersections, and it's often red when the other two are green. In the day time it seemed to be timed with one of the main intersection traffic light.

      The three mile stretch in which the light is on is terrible with traffic lights. My GPS had to add 5 minutes to the estimated time when passing through.
      • 4 Years Ago
      I say the same thing about pedestrians. They should respond to cars not the other way around. Can someone please calculate the amount of gas that can be saved if vehicles are given the right of way instead of cars. All that braking and accelerating is what's causing global warming, or at least part of it!
      • 4 Years Ago
      It's not rocket science. However, individual driver behavior is also to blame for many traffic ailments, such as random jams for no apparent reason.
        • 4 Years Ago
        In parts of Oakland, the lights are perfectly timed so that you have to stop at every single traffic light, it's infuriating. And actually the perfect speed to pass through all of them is way above the speed limit, so in my mind it just encourages speeding.
        • 4 Years Ago
        I cant tell you how annoying traffic lights are. Some stay on green for like 3 seconds, then go back to yellow, then RED.

        Some decide to turn yellow right as you are like 20 feet from the light, going 45 mph.

        I'm not stopping...then again if I do, there goes my brakes.
        • 4 Years Ago
        There is one ridiculously idiotic traffic light in Arlington, MA at an intersection of a not so large city street (Rt. 60) and another pretty large city street (Rt. 2A - Mass Ave.).

        The right turn from Rt. 60 onto Rt. 2A is allowed only from the rightmost lane on a green arrow light, which turns on only AFTER the green light for both sides is done, and it lets only 3-4 cars through. Yes, that's right - no right turn on red, no turn on green, wait for your special arrow light. And Rt. 60 before that intersection is a one-lane road. And it carries a LOT of traffic from a major highway (Rt. 2) into the suburb.

        So what happens is you've got your highway traffic commuters coming home, hitting the light in a jam. Then you've got the right-turners who are stuck on that road because of people going straight, even though there may be no one in the right-turn lane at the intersection. And since the right-turn arrow only lets 3 people through at a time, you start getting right-turners clogging up the main road and blocking everyone who's going straight (or turning left).

        Why the city keeps the right-turn light green for only 5 seconds - boggles the mind.
        I try to stay as far as possible from that intersection within the hours of 3pm to 7 pm.
        • 4 Years Ago
        This is not a new idea. My city (Coquitlam, BC) has used smart traffic lights in almost all intersections as long as I've lived here--small grey box at the corner of the intersection handles the logic.

        It works great--it adjusts its response depending on the traffic flow. If traffic flow is light, it won't trigger left turn lights, or if traffic flow is heavy on one cross road, it keeps the light green longer. Even better: they're all networked together so that if you hit one green and stick close to the speed limit, you'll hit all the other greats 9/10 times. Really saves gas, driver fatigue, and the environment, and has the bonus of adding incentive to stick to the speed limit.

        It's hugely noticeable when I drive into the next city and end up waiting at stoplights while there are absolutely no other cars around; or wind up in a huge queue at a stoplight with way too short a green.
        • 4 Years Ago
        I always thought what we need to do is to deem stop lights are like stop SIGNS after, say, 9:00 pm. That way, if there's no cross traffic, you can pull up, stop, then go.

        Cost = zero. OK, maybe something for driver education and signage.
        • 4 Years Ago
        How about they stop timing the stop lights on the feeder next to tollways to force you to stop at every light? You would assume that they would be more concerned about the environment than their toll revenue. Well, then again...

        Oh, it would be nice if they didn't cut the amber down to a mere half second on the stop light camera enforced lights.


        • 4 Years Ago
        I love it when I hit a traffic jam on the interstate and I'm thinking, well there must be a wreck up here or something or some serious construction, then I find out it's just due to the simpleton rubberneckers slowing down to stare at a fender bender that's pulled way off on the shoulder and is not in and of itself obstructing anything at all.

        Thanks guys!
        • 4 Years Ago
        This doesn't need to cost as much to implement as the engineers think, either. As a biologist, I know you don't need to be physically networked in order to transmit information. The actuators are already underground and do rudimentary signaling. Each traffic light can, on its own, record the moment of peak traffic flow during each light cycle, average that peak timing event over the last 10 light cycles (for instance) to create a moving average of traffic timing, and adjust its signal accordingly. It can even weight certain directions, so main roads get precedence over side roads.

        Someone else said, at nights, all main roads should be a blinking yellow, and all side roads should get a blinking red between, say, midnight and 4 am. There's no since in making a single car idle for 3 minutes to wait out a light cycle.
      • 4 Years Ago
      In some parts of Sweden if a light turns yellow and then it senses another car coming, it will turn back to green until you go through then continue with its cycle.
      • 4 Years Ago
      I've been thinking about this for years. Just think about how much gas it would save.
      • 4 Years Ago
      I live in Panama, this kind of lights or "intelligent lights" as they call them here were a real pain the first weeks, I suppose they were learning, but now they do work and the flow has improved.
        • 4 Years Ago
        The one thing I hate about these is when they are placed in higher-speed zones with low volume cross traffic streets.

        On my commute there is a stretch that turns into state highway and the speed limit travels from 45 to 55 to 60 in about 1 mile. In the 55 zone is a light with a cross street that is really low volume; most of the time I am cruising at 60 miles an hour and then this light flips red on me (and 10 other cars) so that one person can cross the highway. If it had been able to measure relative traffic it would be able to judge that behind the 11 of us who are cruising and have to melt our rotors coming to a stop, there was a huge gap with no traffic that would have made an opportune time to turn, right after we blast through the light.

        I imagine that that many cars screeching to a halt then having to speed back up to 60 again is worse for mileage and CO2 output than making that one car wait 10 - 15 more seconds.
      • 4 Years Ago
      The first time I felt a perceptual difference between car-sensing (induction loop) and timed lights while driving around Quebec City - even at night, with almost no cars on the road, driving seemed like a hassle with all the lights being timed.

      I await the time traffic lights are governed by neural networks and other such adaptive learning algorithms.
      • 4 Years Ago
      This sounds good in theory, but will be difficult to do in practice. The current system, though not perfect or efficient, is very simple, and therefore easier/cheaper to maintain. More complex means more things that could go wrong, such as the light "acting up" in strange ways when a diode wears out in the controlling chip.

      It's frustrating to be sitting at a stop light with no other traffic around, not really sure what the solution is. Maybe human-operated lights at certain select busy intersections, so you'd have a traffic light but someone off to the side that changes it green/red. Essentially just like having a traffic cop there but not having to dangerously stand in the middle of the road. Or along a whole thoroughfare during morning and evening rush hours.

      • 4 Years Ago
      A township near me spent $100K to time their traffic lights. They work great in the morning for people headed into the city, green lights all the way, but were intentionally timed to trap people on their way home at night. You can't catch two green lights to save your life in the evening. This section of road is lined with malls and places to eat so keeping people in the area long enough to force them off the road and into the stores seems to have been the goal. There really needs to be a big push from the public and the federal government to time the lights in such a way the it cuts commute time and just as importantly saves a considerable amount of gas and reduces exhaust emissions. People with more time that spend less money on gas will likely still spend the money these municipalities are so intent on collecting because they are happier, less stressed and have a few extra bucks in their pockets.
        • 4 Years Ago
        Wow, do these people even have brains? I mean, who would think "Gee, this commute is a pain in the ass with all these traffic lights. I'm gonna go shoppin' "

        I'd imagine most people think "Gee, this street is a pain in the ass with all those red lights and shoppers turning right and left... I'm gonna have to cut through 4 residential streets instead"
      • 4 Years Ago
      You're first sentence describes my drive EVERY night after work. Worst part, its one of those intersections that only one side gets to go at a time. So my average wait is 4 minutes waiting for a light to turn all by my lonesome.
      • 4 Years Ago
      Sounds too efficient and logical for the U.S.A. It won't work here.
      • 4 Years Ago
      I like this idea. They should start with with transponders in buses. It would not be too hard to have lights along the bus route turn green as the bus approaches. If buses never had to deal with a red light, they would take the same time or less time than a car to go a given route. This would encourage more folks to leave the car at home and take the bus.
        • 4 Years Ago
        If this were the case I would use the park-and-ride at the north end of my 22 mile commute to work. As is, I could do this but would have to park at 7:30, pick up the bus at 7:40, then it would take me 40 minutes to get to the transit plaza and another 10 to walk to work, putting me there just on time but now 1 hour and 15 minutes invested into commuting one way. Then another 1 hour 15 minutes invested in going back.

        If we didn't hit any lights and could do the trip from north to south and vice versa in 25 minutes, I would almost be making the same time as when I just drive all the way. This would be a win, and really encourage me to use public transit more.
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