# Why Don't All Cities Synchronize Their Traffic Lights? **URL:** \ **Category:** Factual Questions\ **Created:** [November 13, 2001, 1:36am UTC](https://boards.straightdope.com/t/why-dont-all-cities-synchronize-their-traffic-lights/93034 "2001-11-13T01:36:10Z")\ **Posts on this page:** 20\ **Page:** 1
**Author:** ![tsunamisurfer](https://avatars.discourse-cdn.com/v4/letter/t/a698b9/32.png) [@tsunamisurfer](https://boards.straightdope.com/u/tsunamisurfer)\ **Post date:** [November 13, 2001, 1:36am UTC](https://boards.straightdope.com/t/why-dont-all-cities-synchronize-their-traffic-lights/93034/1 "2001-11-13T01:36:10Z")
Seems logical. Synchronizing traffic lights should reduce aggravation, gas consumption, and vehicle wear and tear. Yet, most cities through which I’ve motored have few if any synchronized traffic lights, as though the technology is beyond them. What’s the reason? Does synchronization in certain cases paradoxically increase congestion? Do some lights lack the needed timers? Is it simply a matter of apathy? ---
**Author:** ![robby](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/robby/32/11048_2.png) [@robby](https://boards.straightdope.com/u/robby)\ **Post date:** [November 13, 2001, 1:51am UTC](https://boards.straightdope.com/t/why-dont-all-cities-synchronize-their-traffic-lights/93034/2 "2001-11-13T01:51:19Z")
Well, the town I live in has the lights along Main Street perfectly synchronized. Day or night, whether you drive 20 mph or 60 mph between lights, every single one of them will be red when you reach it. 🙂 To address the OP, I agree that the situation is maddening. I suspect the answer is apathy. ---
**Author:** ![fandango](https://avatars.discourse-cdn.com/v4/letter/f/b5ac83/32.png) [@fandango](https://boards.straightdope.com/u/fandango)\ **Post date:** [November 13, 2001, 1:51am UTC](https://boards.straightdope.com/t/why-dont-all-cities-synchronize-their-traffic-lights/93034/3 "2001-11-13T01:51:54Z")
Some cross streets aren’t as busy, so to put them on a time would mean you might get stopped at them when there is no traffic. What I’d like is for the yellow light to be replaced with an LED countdown so you’d know how long it will last. I’ve seen them do it with crosswalks. ---
**Author:** ![geepee](https://avatars.discourse-cdn.com/v4/letter/g/ebca7d/32.png) [@geepee](https://boards.straightdope.com/u/geepee)\ **Post date:** [November 13, 2001, 2:26am UTC](https://boards.straightdope.com/t/why-dont-all-cities-synchronize-their-traffic-lights/93034/4 "2001-11-13T02:26:02Z")
good idea the countdown timer there was this notorious traffic light in Sheffield outside Angel’s fish emporium that was red for 12 minutes and let two cars through , then back to red. The solution to traffic is synchronised acceleration , watch the cars at a traffic light and you will see a wave pattern go all the way to the back from driver hesistation and or reaction times. Still 12 minutes isn’t as bad as (UL ? ) woman in texas who waited 4 days for a traffic light which happened to be broken ---
**Author:** ![geepee](https://avatars.discourse-cdn.com/v4/letter/g/ebca7d/32.png) [@geepee](https://boards.straightdope.com/u/geepee)\ **Post date:** [November 13, 2001, 2:26am UTC](https://boards.straightdope.com/t/why-dont-all-cities-synchronize-their-traffic-lights/93034/5 "2001-11-13T02:26:03Z")
good idea the countdown timer there was this notorious traffic light in Sheffield outside Angel’s fish emporium that was red for 12 minutes and let two cars through , then back to red. The solution to traffic is synchronised acceleration , watch the cars at a traffic light and you will see a wave pattern go all the way to the back from driver hesistation and or reaction times. Still 12 minutes isn’t as bad as (UL ? ) woman in texas who waited 4 days for a traffic light which happened to be broken ---
**Author:** ![Azazel](https://avatars.discourse-cdn.com/v4/letter/a/838e76/32.png) [@Azazel](https://boards.straightdope.com/u/Azazel)\ **Post date:** [November 13, 2001, 2:38am UTC](https://boards.straightdope.com/t/why-dont-all-cities-synchronize-their-traffic-lights/93034/6 "2001-11-13T02:38:55Z")
Sometimes,in small towns, the lights are deliberately left unsyncronized. It keeps the hotrodders from speeding through the town too fast. ---
**Author:** ![Playdeaux](https://avatars.discourse-cdn.com/v4/letter/p/e99b99/32.png) [@Playdeaux](https://boards.straightdope.com/u/Playdeaux)\ **Post date:** [November 13, 2001, 2:46am UTC](https://boards.straightdope.com/t/why-dont-all-cities-synchronize-their-traffic-lights/93034/7 "2001-11-13T02:46:05Z")
> [@](#): > > \*Originally posted by tsunamisurfer \* > \*\*Seems logical. Synchronizing traffic lights should reduce aggravation, gas consumption, and vehicle wear and tear. Yet, most cities through which I’ve motored have few if any synchronized traffic lights, as though the technology is beyond them. > > What’s the reason? \*\* I once took a microprocessor programming class where the instructor was a guy who actually had done that for a living before giving it up for teacing. I don’t know what the technology’s like now, but it’s probably still a lot more involved than just pushing some buttons. I think it’s also somewhat like flood control - you can’t make a single change without affecting the traffic patterns of an entire area. That takes some planning. The drawback might be that they would actually have to hire some specialist. Hey, _I’d_ pay the extra taxes to cover it! It’s unbelievable to me that a town this size has the kind of gridlock it has. I lived in San Diego and never saw intersections actually come to a complete halt like they do here on any normal weekday. ---
**Author:** ![Derleth](https://avatars.discourse-cdn.com/v4/letter/d/b9e5f3/32.png) [@Derleth](https://boards.straightdope.com/u/Derleth)\ **Post date:** [November 13, 2001, 2:47am UTC](https://boards.straightdope.com/t/why-dont-all-cities-synchronize-their-traffic-lights/93034/8 "2001-11-13T02:47:43Z")
> [@](#): > > \*Originally posted by Azazel \* > \*\*Sometimes,in small towns, the lights are deliberately left unsyncronized. It keeps the hotrodders from speeding through the town too fast. \*\* Bad reason, if that’s the case. Sychronized lights only work if the driver stays at a consistent speed. It’s simple, really: Time the lights so a driver going the limit will hit all greens. That means if it takes 15 minutes to get from one light to the next doing the limit, a given light should be green 15 minutes after its upstream neighbor. If a driver is going too fast or too slow, they will hit reds, hopefully giving them the hint to alter their speed. So, **Azazel** , the small towns you mention are either stupid , lazy, cheap, or amazingly cash-strapped. ---
**Author:** ![Tuckerfan](https://avatars.discourse-cdn.com/v4/letter/t/eada6e/32.png) [@Tuckerfan](https://boards.straightdope.com/u/Tuckerfan)\ **Post date:** [November 13, 2001, 3:04am UTC](https://boards.straightdope.com/t/why-dont-all-cities-synchronize-their-traffic-lights/93034/9 "2001-11-13T03:04:33Z")
Nashvegas (Nashville, TN) recently announced that it was going to be spending something like $1 million dollars to syncronize its traffic lights. When I read that it cost a measly $1 million to do it for a city the size of Nashvegas, I immediately thought, “Cripes! Why the hell didn’t they do it sooner?” So apparently, its not all that expensive to do. Why more cities don’t do it is a good question. ---
**Author:** ![Another\_Primate](https://avatars.discourse-cdn.com/v4/letter/a/f19dbf/32.png) [@Another\_Primate](https://boards.straightdope.com/u/Another_Primate)\ **Post date:** [November 13, 2001, 3:10am UTC](https://boards.straightdope.com/t/why-dont-all-cities-synchronize-their-traffic-lights/93034/10 "2001-11-13T03:10:15Z")
> [@](#): > > \*Originally posted by Derleth \* > \*\*Bad reason, if that’s the case. Sychronized lights only work if the driver stays at a consistent speed. If a driver is going too fast or too slow, they will hit reds, hopefully giving them the hint to alter their speed. So, **Azazel** , the small towns you mention are either stupid , lazy, cheap, or amazingly cash-strapped. \*\* **Derleth** , my town has synchronized lights on the two main drags, and they’re really nice. But we sure have a lot of intersection accidents, and I think the synched lights are one reason. When everyone on the main street is driving the right speed, you all approach the lights at 25 mph. An idiot running a yellow/red on a cross street (because he doesn’t see anyone stopped at the light) will get hit at 25, because even though the light we’re approaching is red, we all KNOW it’s going to change by the time we get there, so we don’t slow down. One other annoying thing about synchronized lights is the bonehead driver (on the main drag) who races to each light, stops, races, stops… sometimes I’m in the lane next to one, and we just pass each other the whole way through town. Makes me laugh – when is he going to figure it out? – unless he decides to pull in front of me. However, I still vote for synchronized lights. ---
**Author:** ![tsunamisurfer](https://avatars.discourse-cdn.com/v4/letter/t/a698b9/32.png) [@tsunamisurfer](https://boards.straightdope.com/u/tsunamisurfer)\ **Post date:** [November 13, 2001, 3:31am UTC](https://boards.straightdope.com/t/why-dont-all-cities-synchronize-their-traffic-lights/93034/11 "2001-11-13T03:31:11Z")
Most of the examples cited above involve small towns. I specified cities, as it seems likely that small municipalities lack the engineering talent and technology to effect such change. Not so for medium to large cities. Playdeaux is correct: a large-scale synchronization plan would require precision planning and engineering, and I’m guessing politics factors the entire calculus inasmuch as some voters are going to be peeved with change/added inconvenience. Moreover, some motorists would have to wait _longer_ at some intersections. That said, synchronization of traffic lights seems so intuitively obvious. ---
**Author:** ![Ring](https://avatars.discourse-cdn.com/v4/letter/r/6a8cbe/32.png) [@Ring](https://boards.straightdope.com/u/Ring)\ **Post date:** [November 13, 2001, 3:55am UTC](https://boards.straightdope.com/t/why-dont-all-cities-synchronize-their-traffic-lights/93034/12 "2001-11-13T03:55:50Z")
If they’re sychronized in one direction are they sychronized in both directions? I could figure this out, but it would be easier if someone knew off the top of their head. ---
**Author:** ![Playdeaux](https://avatars.discourse-cdn.com/v4/letter/p/e99b99/32.png) [@Playdeaux](https://boards.straightdope.com/u/Playdeaux)\ **Post date:** [November 13, 2001, 4:09am UTC](https://boards.straightdope.com/t/why-dont-all-cities-synchronize-their-traffic-lights/93034/13 "2001-11-13T04:09:02Z")
> [@](#): > > \*Originally posted by Ring \* > \*\*If they’re sychronized in one direction are they sychronized in both directions? I could figure this out, but it would be easier if someone knew off the top of their head. \*\* It depends on the traffic flow on the intersecting roads. Ideally, the whole concept should provide optimum traffic flow & give preference to high traffic roads over small feeder roads. ---
**Author:** ![TwistofFate](https://avatars.discourse-cdn.com/v4/letter/t/cdc98d/32.png) [@TwistofFate](https://boards.straightdope.com/u/TwistofFate)\ **Post date:** [November 13, 2001, 2:25pm UTC](https://boards.straightdope.com/t/why-dont-all-cities-synchronize-their-traffic-lights/93034/14 "2001-11-13T14:25:02Z")
> [@](#): > > What I’d like is for the yellow light to be replaced with an LED countdown so you’d know how long it will last. I’ve seen them do it with crosswalks I am not a behavioural scientist, but wouldnt that just encourage people to excessive speed off at the change of the lights (ala Formula 1)? ---
**Author:** ![The\_Great\_Gazoo](https://avatars.discourse-cdn.com/v4/letter/t/67e7ee/32.png) [@The\_Great\_Gazoo](https://boards.straightdope.com/u/The_Great_Gazoo)\ **Post date:** [November 13, 2001, 2:52pm UTC](https://boards.straightdope.com/t/why-dont-all-cities-synchronize-their-traffic-lights/93034/15 "2001-11-13T14:52:41Z")
> [@](#): > > \*Originally posted by fandango \* > \*\*What I’d like is for the yellow light to be replaced with an LED countdown so you’d know how long it will last. \*\* Yeah, that’s a good idea :rolleyes: 🙂 Let’s give the cars a chance to see exactly when the light will change. Ooh, I have 3 seconds! Better gun it! With the clowns jumping the gun on the red to green and the the bozos gunning it to catch a light, I forsee chaos. And a complete nightmare for pedestrians. My feeling on the pedestrian countdown is that it is OK as long as the drivers can’t see it. ---
**Author:** ![lucwarm](https://avatars.discourse-cdn.com/v4/letter/l/e19adc/32.png) [@lucwarm](https://boards.straightdope.com/u/lucwarm)\ **Post date:** [November 13, 2001, 3:36pm UTC](https://boards.straightdope.com/t/why-dont-all-cities-synchronize-their-traffic-lights/93034/16 "2001-11-13T15:36:25Z")
> [@](#): > > \*Originally posted by Ring \* > \*\*If they’re sychronized in one direction are they sychronized in both directions? I could figure this out, but it would be easier if someone knew off the top of their head. \*\* If you have a two-way street, and you make it a basic progressive pattern in one direction, you will really make life miserable for people going in the other direction. I drive in Manhattan every day (where all the lights are in synch), and most of the one-way streets follow a so-called “progressive” pattern, i.e. you can “surf the wave” of green lights. During rush hour, many of the two-way streets are put on a “progressive” pattern, for example, 8th avenue between 110th street and 155th street. If you are in the unfortunate situation of going towards mid-town between 4:00pm and 7:00pm on one of these streets, life is pretty miserable – you can see the “wave” of green lights coming towards you, followed by a “wave” of red lights. When the green finally hits you, you can only make it 5 or 6 blocks or so before you hit red again. The more common way to synch lights on a two-way street is to have a “simultaneous” pattern, where all the lights turn green for a set period in both directions. Of course, this encourages speeding since the natural goal is to make it as many blocks as possible during the green time. In light traffic, at a reasonable speed, you can usually go 9 or 10 blocks in Manhattan on a “simultanous” pattern street. Of course with a progressive pattern, the sky’s the limit - I’ve made it over 100 blocks without hitting red. And if you’re going against a progressive pattern, well . . fuhgettaboutit! ---
**Author:** ![lucwarm](https://avatars.discourse-cdn.com/v4/letter/l/e19adc/32.png) [@lucwarm](https://boards.straightdope.com/u/lucwarm)\ **Post date:** [November 13, 2001, 3:48pm UTC](https://boards.straightdope.com/t/why-dont-all-cities-synchronize-their-traffic-lights/93034/17 "2001-11-13T15:48:12Z")
> [@](#): > > \*Originally posted by lucwarm \* > \*\* > > I drive in Manhattan every day (where all the lights are in synch), and most of the one-way streets follow a so-called “progressive” pattern, i.e. you can “surf the wave” of green lights. > > \*\* Oops, I should have said “avenue” not street. i.e. most of the synchronization is on the long north-south roads in Manhattan. What’s interesting is that the’ve managed to synchronize some of the cross-streets too. For example, 57th Street from west to east. This is pretty impressive when you consider that 57th street crosses many north-south avenues, some one-way, some two-way, and each with its own pattern. ---
**Author:** ![yabob](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/yabob/32/2821_2.png) [@yabob](https://boards.straightdope.com/u/yabob)\ **Post date:** [November 13, 2001, 4:15pm UTC](https://boards.straightdope.com/t/why-dont-all-cities-synchronize-their-traffic-lights/93034/18 "2001-11-13T16:15:25Z")
Oakland deliberately desynchronised some of the lights on downtown streets that they didn’t want through traffic to use, and put up signs - “traffic lights not coordinated, use \*\*\*\*” directing traffic two blocks over. The signage went up on a major street that people were definitely in the habit of driving through town on, and the traffic planners didn’t like it. Traffic studies are non-trivial, BTW. Don’t focus on the technology involved, or its cost - it’s modeling the traffic patterns to predict the effects of applying the technology that’s the kicker. And the politics, as somebody else alluded to. ---
**Author:** ![RGillen](https://avatars.discourse-cdn.com/v4/letter/r/848f3c/32.png) [@RGillen](https://boards.straightdope.com/u/RGillen)\ **Post date:** [November 13, 2001, 4:43pm UTC](https://boards.straightdope.com/t/why-dont-all-cities-synchronize-their-traffic-lights/93034/19 "2001-11-13T16:43:32Z")
OK, I brought this up with a former engineer for the Ohio Dept. of Transportation, so technically it only applies to highways in Ohio, but it’s probably reasonably universal. When lights are set up and timing needs to be arranged, or when a request is made to alter the timing, a study is done (in ODOT’s case by a contractor) on traffic flow, etc. that takes at least 6 months and is not cheap (sorry, I don’t have any exact cost numbers, but it’s in the neighborhood of hundreds of thousands of dollars). It’s not nearly as simple as “how long does it take to get to the next light if you drive the speed limit.” You have to consider how far traffic will back up behind a red light. You have to consider increase in traffic flow during rush hour. You have to consider backups on cross streets. What if two major streets cross? Which is more important and gets its timing preserved? What about businesses or homes along the street? Anyway, it is no simple task. Besides, they don’t do it to save wear and tear on your car, they do it to move traffic through the city faster and make intersections safer. I know nothing about the city of Nashville or its project, but based on this, $1M might get you a few streets, not the entire city. Even for one large highway, some serious computer simulation is involved. A city or even a Manhattan avenue must be a nightmare. The idea of making traffic better is intuitive, but defining “better” is tough. Trying to enter the synchronized street outside my office at 5pm is a pain - by the time I get a green light, there is too much backup to even get on the street. No matter how much time or money you throw at it, nobody will be satisfied all the time. I would stop short of calling cities without synchronized lights stupid or lazy. ---
**Author:** ![drachillix](https://avatars.discourse-cdn.com/v4/letter/d/48db29/32.png) [@drachillix](https://boards.straightdope.com/u/drachillix)\ **Post date:** [November 13, 2001, 6:50pm UTC](https://boards.straightdope.com/t/why-dont-all-cities-synchronize-their-traffic-lights/93034/20 "2001-11-13T18:50:06Z")
> [@](#): > > \*Originally posted by RGillen \* > \*\*When lights are set up and timing needs to be arranged, or when a request is made to alter the timing, a study is done (in ODOT’s case by a contractor) on traffic flow, etc. that takes at least 6 months and is not cheap (sorry, I don’t have any exact cost numbers, but it’s in the neighborhood of hundreds of thousands of dollars). \*\* Sounds like a business to be in! I guess the coolest thing would be to invent some kind of affordable networked sensor system so that a central computer could monitor traffic flow and keep things moving consistently no matter what time of day by modifying light duration as needed. Are there any cities that use something like this? [Next page](https://boards.straightdope.com/t/why-dont-all-cities-synchronize-their-traffic-lights/93034.md?page=2)