# Unethical Traffic Light? **URL:** \ **Category:** Factual Questions\ **Created:** [February 4, 2011, 1:47pm UTC](https://boards.straightdope.com/t/unethical-traffic-light/570140 "2011-02-04T13:47:12Z")\ **Posts on this page:** 20\ **Page:** 2
**Author:** ![Dallas\_Jones](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/dallas_jones/32/3277_2.png) [@Dallas\_Jones](https://boards.straightdope.com/u/Dallas_Jones)\ **Post date:** [February 4, 2011, 5:07pm UTC](https://boards.straightdope.com/t/unethical-traffic-light/570140/21 "2011-02-04T17:07:30Z")
Here is a link to the National Motorists blog that has several articles about the manipulation of yellow traffic light timing. [http://www.motorists.org/red-light-cameras/yellow-lights](http://www.motorists.org/red-light-cameras/yellow-lights) Among the interesting studies and articles, you might find this one informative about six cities that were caught shortening the yellow light timing for _profit_. [http://blog.motorists.org/6-cities-that-were-caught-shortening-yellow-light-times-for-profit/](http://blog.motorists.org/6-cities-that-were-caught-shortening-yellow-light-times-for-profit/) ---
**Author:** ![x-ray\_vision](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/x-ray_vision/32/351_2.png) [@x-ray\_vision](https://boards.straightdope.com/u/x-ray_vision)\ **Post date:** [February 4, 2011, 5:08pm UTC](https://boards.straightdope.com/t/unethical-traffic-light/570140/22 "2011-02-04T17:08:45Z")
> [@Exapno\_Mapcase](#): > > Either way, traffic engineering is not something done at the whims of a guy sitting in an office and saying that the city needs more revenue. Any change in any light ripples out and affects the entire system. There are state and national standards that need to be met. Every tiny increment is planned out well in advance. And those standards are often not met. I don’t think it’s out of the question to conclude that there could be a profit motive. [6 Cities That Were Caught Shortening Yellow Light Times For Profit](http://blog.motorists.org/6-cities-that-were-caught-shortening-yellow-light-times-for-profit/) The title of the article may be misleading, since in many of the cases there isn’t enough evidence in the article to suggest the yellow lights were short for profit in all of the cases, but it sure as hell looks more than suspicious. ETA: Damn! A minute too late. ---
**Author:** ![ManiacMan](https://avatars.discourse-cdn.com/v4/letter/m/b782af/32.png) [@ManiacMan](https://boards.straightdope.com/u/ManiacMan)\ **Post date:** [February 4, 2011, 5:11pm UTC](https://boards.straightdope.com/t/unethical-traffic-light/570140/23 "2011-02-04T17:11:15Z")
Wow Dallas thanks! ---
**Author:** ![Telemark](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/telemark/32/372_2.png) [@Telemark](https://boards.straightdope.com/u/Telemark)\ **Post date:** [February 4, 2011, 5:15pm UTC](https://boards.straightdope.com/t/unethical-traffic-light/570140/24 "2011-02-04T17:15:12Z")
> [@ManiacMan](#): > > I don’t think that some person is sitting in a room somewhere adjusting a timer to decrease the interval from yellow-to-red. But when other lights that are on the same road all have larger intervals I can only conclude that it is a scam of sorts. Then you haven’t been reading the answers given on this thread. There are many legitimate reasons why they times could be different, all posted upthread. ---
**Author:** ![Chessic\_Sense](https://avatars.discourse-cdn.com/v4/letter/c/7c8e57/32.png) [@Chessic\_Sense](https://boards.straightdope.com/u/Chessic_Sense)\ **Post date:** [February 4, 2011, 5:26pm UTC](https://boards.straightdope.com/t/unethical-traffic-light/570140/25 "2011-02-04T17:26:14Z")
In Virginia, the [law says](http://leg1.state.va.us/cgi-bin/legp504.exe?000+cod+46.2-833): > [@](#): > > Steady amber indicates that a change is about to be made in the direction of the moving of traffic. When the amber signal is shown, traffic which has not already entered the intersection, including the crosswalks, shall stop **if it is not reasonably safe to continue** So there you go. In my state, you only have to stop if it’s not safe to keep going. That’s helpful. :rolleyes: But if you Google “yellow light timing”, you’ll get a bunch of results that pertain to the question at hand. Cities can and do shorten or lengthen yellow lights. ---
**Author:** ![ManiacMan](https://avatars.discourse-cdn.com/v4/letter/m/b782af/32.png) [@ManiacMan](https://boards.straightdope.com/u/ManiacMan)\ **Post date:** [February 4, 2011, 5:34pm UTC](https://boards.straightdope.com/t/unethical-traffic-light/570140/26 "2011-02-04T17:34:32Z")
> [@Telemark](#): > > Then you haven’t been reading the answers given on this thread. There are many legitimate reasons why they times could be different, all posted upthread. Yes. I. Have. I understand that the lights themselves can vary. However, the way the system “works” is that law enforcement can gorge on victims who are unfamiliar with a certain light’s operation. Despite all the math and science it boils down to a light that allows a city to reap rewards either through purposeful manipulation, or convienent side effects of a “complex” “highly confusing” system that keeps are roadways “safe” and “moving freely”. I don’t understand how shortening the yellow-red interval can improve traffic flow. Its about how long the light is green or red for a particular road, not how long it takes for a light to change from yellow to red. Yellow to red interval is more about how much money a city brings in IMO. ---
**Author:** ![Voyager](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/voyager/32/133_2.png) [@Voyager](https://boards.straightdope.com/u/Voyager)\ **Post date:** [February 4, 2011, 5:45pm UTC](https://boards.straightdope.com/t/unethical-traffic-light/570140/27 "2011-02-04T17:45:23Z")
> [@VernWinterbottom](#): > > It has always been my understanding that a yellow light is a warning to driver that the light is seconds away from changing to red so you had better be prepared to stop. > > It certainly doesn’t mean “just keep on driving” or “speed up to beat the light.” > > There’s really no such thing as running a yellow light. But when the light is red, you are NOT supposed to be moving. In California red light cameras only trigger if you enter an intersection on the red, and not if the light turns red while you are in the intersection - and certainly not if you enter on a yellow. I believe that if you show a light is not timed according to standards you can beat a ticket. You’d have to go there and study it though. ---
**Author:** ![Voyager](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/voyager/32/133_2.png) [@Voyager](https://boards.straightdope.com/u/Voyager)\ **Post date:** [February 4, 2011, 5:49pm UTC](https://boards.straightdope.com/t/unethical-traffic-light/570140/28 "2011-02-04T17:49:31Z")
> [@ManiacMan](#): > > So a traffic light is meant to keep the flow of traffic moving, but nevermind the delay that the other commuters experienced when I was actually pulled over. Not to mention all of the other commuters who increased other commuters delays when they rubbernecked and gawked while hitting their brakes to check out those pretty blue and red flashing lights. > > When I got popped it was snowing and the road was slippery. I don’t know what the friction coefficient was reduced to, but I was slipping and sliding as I made my initial way to the road that I was pulled over on and thought I had better drive carefully. So IMO I couldn’t have stopped safely because of the conditions… Wait - conditions were bad and you were driving fast enough to not be able to stop in the time of the yellow light, even reduced? When I drove in snow I sure as hell started to stop the moment I saw that light turn yellow (unless some clown was on my tail.) It seems you were driving too fast for conditions. If it was a clear, dry, day I’d have a lot more sympathy. ---
**Author:** ![Pasta](https://avatars.discourse-cdn.com/v4/letter/p/ecccb3/32.png) [@Pasta](https://boards.straightdope.com/u/Pasta)\ **Post date:** [February 4, 2011, 5:49pm UTC](https://boards.straightdope.com/t/unethical-traffic-light/570140/29 "2011-02-04T17:49:59Z")
> [@minor7flat5](#): > > The reason for my puzzlement: Why bother have a yellow light at all? What purpose does it serve? > > If Yellow means the same as Red (i.e. “Don’t go through the intersection”), then why don’t they simply have red and green lights? Yellow is not red. When the light turns yellow, you should immediately assess whether you can safely come to a stop. If yes, then stop. If no, then proceed. It’s no more complicated than that. The duration of the light has nothing to do with your decision directly – it is supposed to be set so that someone making an honest assessment that they cannot stop will be through the intersection before cross traffic is given a green. A yellow specifically shouldn’t induce the question that it does for most people: “Can I make it through the intersection before it turns red?” The question is supposed to be “Can I safely stop before I reach the line?” Note that the latter question doesn’t depend on the yellow’s duration. ---
**Author:** ![x-ray\_vision](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/x-ray_vision/32/351_2.png) [@x-ray\_vision](https://boards.straightdope.com/u/x-ray_vision)\ **Post date:** [February 4, 2011, 6:02pm UTC](https://boards.straightdope.com/t/unethical-traffic-light/570140/30 "2011-02-04T18:02:17Z")
> [@Voyager](#): > > When I drove in snow I sure as hell started to stop the moment I saw that light turn yellow (unless some clown was on my tail.) It seems you were driving too fast for conditions. If it was a clear, dry, day I’d have a lot more sympathy. Unless someone was on your tail, you’d start to stop the moment you saw light turn yellow regardless of at what point at or near the intersection you were? That’s not what you’re supposed to do, especially in snowy conditions. I don’t see how you concluded that **ManiacMan** was going too fast for conditions because he went through a yellow light. ---
**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:** [February 4, 2011, 6:11pm UTC](https://boards.straightdope.com/t/unethical-traffic-light/570140/31 "2011-02-04T18:11:04Z")
> [@Pasta](#): > > Yellow is not red. When the light turns yellow, you should immediately assess whether you can safely come to a stop. If yes, then stop. If no, then proceed. It’s no more complicated than that. The duration of the light has nothing to do with your decision directly – it is supposed to be set so that someone making an honest assessment that they cannot stop will be through the intersection before cross traffic is given a green. > > A yellow specifically shouldn’t induce the question that it does for most people: “Can I make it through the intersection before it turns red?” The question is supposed to be “Can I safely stop before I reach the line?” Note that the latter question doesn’t depend on the yellow’s duration. This is basically the correct way to look at it for the driver. The details of how it is enforced differ with jurisdictions. Some may ticket if you haven’t cleared the intersection by the red light, probably on the grounds that you either tried to squeeze through the yellow light, or weren’t paying enough attention and didn’t see it turn yellow when you could have stopped. The OP’s complaint has some weight in such jurisdictions. Something of a hijack - there’s another circumstance where one may be in the middle of an intersection under the red light: pulling out into the intersection before backed up traffic has cleared on the other side. You may have even entered on the green. Jurisdictions differ on how to ticket for “blocking the box”, too. Several years ago, San Francisco started handing out tickets for this, and they were all thrown out by the courts. It was just rude, not illegal. ---
**Author:** ![ManiacMan](https://avatars.discourse-cdn.com/v4/letter/m/b782af/32.png) [@ManiacMan](https://boards.straightdope.com/u/ManiacMan)\ **Post date:** [February 4, 2011, 6:47pm UTC](https://boards.straightdope.com/t/unethical-traffic-light/570140/32 "2011-02-04T18:47:43Z")
> [@Voyager](#): > > Wait - conditions were bad and you were driving fast enough to not be able to stop in the time of the yellow light, even reduced? When I drove in snow I sure as hell started to stop the moment I saw that light turn yellow (unless some clown was on my tail.) It seems you were driving too fast for conditions. If it was a clear, dry, day I’d have a lot more sympathy. I was keeping up with the flow of traffic. The cop himself said that he had clocked over 100 people in the past hour at 30-31 mph. Its more like I was driving too fast for a light that has a 3.5s yellow-red interval. ---
**Author:** ![Telemark](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/telemark/32/372_2.png) [@Telemark](https://boards.straightdope.com/u/Telemark)\ **Post date:** [February 4, 2011, 6:54pm UTC](https://boards.straightdope.com/t/unethical-traffic-light/570140/33 "2011-02-04T18:54:58Z")
> [@ManiacMan](#): > > I don’t understand how shortening the yellow-red interval can improve traffic flow. Its about how long the light is green or red for a particular road, not how long it takes for a light to change from yellow to red. Actually, the entire light cycle affects traffic flow. In particular the speed and density of traffic may dictate how long a yellow light should stay illuminated. You don’t cars stopping too soon - that would reduce the flow through the intersection. But you don’t want too many cars trying to race the red, and end up with accidents and/or gridlock. Differing traffic patterns at different times of day may make for different optimal timings. Also the traffic makeup (cars vs big trucks) may dictate how long you need to clear the intersection. At certain times of day they may expect more trucks and need to keep the yellow for longer to allow them to make it all the way through. Either way, there’s little indication other than the fact that you were pulled over that the city is doing this for revenue purposes. If you want real answers you should talk to your city’s highway department and ask them about the intersection in question. ---
**Author:** ![ClaytonThroop](https://avatars.discourse-cdn.com/v4/letter/c/e99b99/32.png) [@ClaytonThroop](https://boards.straightdope.com/u/ClaytonThroop)\ **Post date:** [February 4, 2011, 7:09pm UTC](https://boards.straightdope.com/t/unethical-traffic-light/570140/34 "2011-02-04T19:09:39Z")
> [@ManiacMan](#): > > I was keeping up with the flow of traffic. The cop himself said that he had clocked over 100 people in the past hour at 30-31 mph. Its more like I was driving too fast for a light that has a 3.5s yellow-red interval. According to what was posted upthread, 3.5 seconds is standard for a 35 mph road. Just because everyone else was driving too fast for conditions, doesn’t somehow make the standard unethical. But maybe I’m a little biased, having been almost killed by someone who, eh, was driving too fast for a light with a 3.5s yellow-red interval. ---
**Author:** ![Skywatcher](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/skywatcher/32/254_2.png) [@Skywatcher](https://boards.straightdope.com/u/Skywatcher)\ **Post date:** [February 4, 2011, 7:12pm UTC](https://boards.straightdope.com/t/unethical-traffic-light/570140/35 "2011-02-04T19:12:22Z")
> [@yabob](#): > > This is basically the correct way to look at it for the driver. The details of how it is enforced differ with jurisdictions. Some may ticket if you haven’t cleared the intersection by the red light, probably on the grounds that you either tried to squeeze through the yellow light, or weren’t paying enough attention and didn’t see it turn yellow when you could have stopped. Or were behind a vehicle in an ajacent lane and that vehicle stopped but you didn’t. ---
**Author:** ![Peremensoe](https://avatars.discourse-cdn.com/v4/letter/p/ce7236/32.png) [@Peremensoe](https://boards.straightdope.com/u/Peremensoe)\ **Post date:** [February 4, 2011, 7:25pm UTC](https://boards.straightdope.com/t/unethical-traffic-light/570140/36 "2011-02-04T19:25:34Z")
> [@Pasta](#): > > When the light turns yellow, you should immediately assess whether you can safely come to a stop. If yes, then stop. If no, then proceed. It’s no more complicated than that. The duration of the light has nothing to do with your decision directly – it is supposed to be set so that someone making an honest assessment that they cannot stop will be through the intersection before cross traffic is given a green. That’s right. In short, a difference in signal light duration shouldn’t make any difference at all in how you drive. ---
**Author:** ![ManiacMan](https://avatars.discourse-cdn.com/v4/letter/m/b782af/32.png) [@ManiacMan](https://boards.straightdope.com/u/ManiacMan)\ **Post date:** [February 4, 2011, 7:41pm UTC](https://boards.straightdope.com/t/unethical-traffic-light/570140/37 "2011-02-04T19:41:45Z")
> [@Telemark](#): > > Either way, there’s little indication other than the fact that you were pulled over that the city is doing this for revenue purposes. If the police are passing out tickets 10x more a day when the light is timed to 3.5s I would say that would be plenty enough indication. I haven’t camped out to observe this intersection, but then I don’t need to. The police are always there when the light is “fast” and they are not when it is “slow”. Usually, they are further south getting people for speeding. They go to where the easy pickings are to be had. ---
**Author:** ![Telemark](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/telemark/32/372_2.png) [@Telemark](https://boards.straightdope.com/u/Telemark)\ **Post date:** [February 4, 2011, 7:52pm UTC](https://boards.straightdope.com/t/unethical-traffic-light/570140/38 "2011-02-04T19:52:29Z")
Perhaps the light being “fast” and the police presence are both there for the same reason - increased accidents during that time of day. Correlation does not equal causation. ---
**Author:** ![Bearflag70](https://avatars.discourse-cdn.com/v4/letter/b/8e7dd6/32.png) [@Bearflag70](https://boards.straightdope.com/u/Bearflag70)\ **Post date:** [February 4, 2011, 7:52pm UTC](https://boards.straightdope.com/t/unethical-traffic-light/570140/39 "2011-02-04T19:52:57Z")
Q: What does a yellow light mean? A: [Slow down](http://www.youtube.com/watch?v=j6FmbMiIxws). 😃 ---
**Author:** ![ManiacMan](https://avatars.discourse-cdn.com/v4/letter/m/b782af/32.png) [@ManiacMan](https://boards.straightdope.com/u/ManiacMan)\ **Post date:** [February 4, 2011, 7:58pm UTC](https://boards.straightdope.com/t/unethical-traffic-light/570140/40 "2011-02-04T19:58:22Z")
> [@spark240](#): > > That’s right. In short, a difference in signal light duration shouldn’t make any difference at all in how you drive. I disagree. 35mph is approx. 51 feet per sec. If I am about 150 feet away and that light turns yellow I have to take in a bunch of factors before making my decision to stop. Is someone tailgetting me? Is the road dry? Wet? Slipppery? Those are just what comes to to top of my head. Subtract an indivuals reaction time which can be .5s to .75s and the amount of time u have to react and make a decision to stop safely is too short. And that’s my problem. People need more time than 3-3.5 seconds and the cops know this and they profit. [Previous page](https://boards.straightdope.com/t/unethical-traffic-light/570140.md?page=1) [Next page](https://boards.straightdope.com/t/unethical-traffic-light/570140.md?page=3)