# Traffic light question **URL:** \ **Category:** In My Humble Opinion\ **Created:** [February 22, 2018, 6:52pm UTC](https://boards.straightdope.com/t/traffic-light-question/809357 "2018-02-22T18:52:22Z")\ **Posts on this page:** 20\ **Page:** 2
**Author:** ![StraightTalk](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/straighttalk/32/9982_2.png) [@StraightTalk](https://boards.straightdope.com/u/StraightTalk)\ **Post date:** [February 22, 2018, 9:01pm UTC](https://boards.straightdope.com/t/traffic-light-question/809357/21 "2018-02-22T21:01:24Z")
> [@Dinsdale](#): > > My wife just arbitrated a lawsuit over traffic accident, and asked me this question. Say you are heading west on a street, and as you approach an intersection, the traffic light facing you turns yellow and then red. If there is no sign saying “Oncoming traffic has longer green”, can you assume that the light controlling eastbound traffic changes colors at the same time? > > In this case, the guy heading W was in the intersection, waiting to turn L. He said the light turned red, so he turned to clear the intersection. A eastbound driver coming from the west struck him as he turned. My wife’s question was, if she found the W-bound driver credible, could she assume the E-bound driver blew a red light. > > I’d imagine one MIGHT be able to call the village/state, and find out how they are controlled. But we were just wondering if there is some general convention. FTR, she says yes, they do change at the same time. I say no - basically because I never trust anyone or anything to make sense while I drive! 😉 You can assume that the other traffic light turns red at the same time. You cannot assume that any other driver has any sense whatsoever. ---
**Author:** ![jz78817](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/jz78817/32/1028_2.png) [@jz78817](https://boards.straightdope.com/u/jz78817)\ **Post date:** [February 22, 2018, 9:06pm UTC](https://boards.straightdope.com/t/traffic-light-question/809357/22 "2018-02-22T21:06:08Z")
> [@StraightTalk](#): > > You can assume that the other traffic light turns red at the same time. no you cannot. ---
**Author:** ![kanicbird](https://avatars.discourse-cdn.com/v4/letter/k/5f8ce5/32.png) [@kanicbird](https://boards.straightdope.com/u/kanicbird)\ **Post date:** [February 22, 2018, 9:07pm UTC](https://boards.straightdope.com/t/traffic-light-question/809357/23 "2018-02-22T21:07:58Z")
You should not assume the light is working at all, and perhaps everything is green in every direction. Though we can’t live with this and be sane, so we need to assume things that are reasonable, and expected. In this case I would say that the left turner should have reasonable assumption that the oncoming traffic is stopping, not just that the light has changed. ---
**Author:** ![jz78817](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/jz78817/32/1028_2.png) [@jz78817](https://boards.straightdope.com/u/jz78817)\ **Post date:** [February 22, 2018, 9:11pm UTC](https://boards.straightdope.com/t/traffic-light-question/809357/24 "2018-02-22T21:11:44Z")
> [@kanicbird](#): > > You should not assume the light is working at all, and perhaps everything is green in every direction. Though we can’t live with this and be sane, so we need to assume things that are reasonable, and expected. In this case I would say that the left turner should have reasonable assumption that the oncoming traffic is stopping, not just that the light has changed. as I noted earlier, in my area asymmetrical timing is very common. it would be extremely unwise to assume the state of signals you can’t see. ---
**Author:** ![Spiderman](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/spiderman/32/230_2.png) [@Spiderman](https://boards.straightdope.com/u/Spiderman)\ **Post date:** [February 22, 2018, 9:37pm UTC](https://boards.straightdope.com/t/traffic-light-question/809357/25 "2018-02-22T21:37:14Z")
> [@Riemann](#): > > Are you claiming that westbound left turners are not separately controlled, and that a westbound left turner could be left stranded in the middle of the junction long after his light has turned red, still waiting for eastbound straight-on traffic to stop? Excuse my skepticism, but I have never seen this anywhere in decades of deriving. It would be extremely dangerous, and I don’t believe that junctions are ever set up this way. [Opticoms](http://www.gtt.com/opticom-emergency-response/) are by definition always setup this way even if they are infrequently triggered. Opticoms are activated by emergency vehicles; they turn every light (straight & turn arrows) green in the direction that the emergency vehicle is traveling while turning every opposing direction red to help move traffic out of the way & prevent so much slow down at intersections so that the emergency vehicle can get to the emergency. Depending upon road elevation & line of sight distance, they can be activated by an emergency vehicle blocks away even if that vehicle turns or stops before the intersection. I’ve been ‘caught’ a couple of times by a cop who made a traffic stop on the street I was crossing. He still had his opticom activated so the light wouldn’t change for anyone else even though he was parked & out of his car already. ---
**Author:** ![Riemann](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/riemann/32/3133_2.png) [@Riemann](https://boards.straightdope.com/u/Riemann)\ **Post date:** [February 22, 2018, 9:37pm UTC](https://boards.straightdope.com/t/traffic-light-question/809357/26 "2018-02-22T21:37:45Z")
> [@jz78817](#): > > as I noted earlier, in my area asymmetrical timing is very common. it would be extremely unwise to assume the state of signals you can’t see. There are many parts of the U.S. that I haven’t driven in, but I’m astonished that this is the case. It seems incredibly dangerous. May I ask what state you are in? ---
**Author:** ![Channing\_Idaho\_Banks](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/channing_idaho_banks/32/250_2.png) [@Channing\_Idaho\_Banks](https://boards.straightdope.com/u/Channing_Idaho_Banks)\ **Post date:** [February 22, 2018, 11:05pm UTC](https://boards.straightdope.com/t/traffic-light-question/809357/27 "2018-02-22T23:05:08Z")
> [@Riemann](#): > > There are many parts of the U.S. that I haven’t driven in, but I’m astonished that this is the case. It seems incredibly dangerous. May I ask what state you are in? I’m guessing Sugarland Texas. ---
**Author:** ![jz78817](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/jz78817/32/1028_2.png) [@jz78817](https://boards.straightdope.com/u/jz78817)\ **Post date:** [February 23, 2018, 12:32am UTC](https://boards.straightdope.com/t/traffic-light-question/809357/28 "2018-02-23T00:32:57Z")
> [@Riemann](#): > > There are many parts of the U.S. that I haven’t driven in, but I’m astonished that this is the case. It seems incredibly dangerous. May I ask what state you are in? Michigan. But I don’t think it’s done unless there’s also a left turn signal present. ---
**Author:** ![Riemann](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/riemann/32/3133_2.png) [@Riemann](https://boards.straightdope.com/u/Riemann)\ **Post date:** [February 23, 2018, 1:48am UTC](https://boards.straightdope.com/t/traffic-light-question/809357/29 "2018-02-23T01:48:23Z")
> [@jz78817](#): > > Michigan. But I don’t think it’s done unless there’s also a left turn signal present. Ah, ok, fine. Asymmetric timing is common here too, but that was the point - it always requires left turn control. ---
**Author:** ![jz78817](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/jz78817/32/1028_2.png) [@jz78817](https://boards.straightdope.com/u/jz78817)\ **Post date:** [February 23, 2018, 3:01am UTC](https://boards.straightdope.com/t/traffic-light-question/809357/30 "2018-02-23T03:01:03Z")
> [@Riemann](#): > > Ah, ok, fine. Asymmetric timing is common here too, but that was the point - it always requires left turn control. yeah, typically the way it works if you’re on the side with the shorter timing: - the thru lanes will have the green light, while you wait in the left turn lane with a flashing yellow arrow\* (indicating you can turn if clear but oncoming traffic has a green and the right of way) - the thru lanes on your side will change to red, stopping thru traffic. - you _still_ have a flashing yellow arrow, indicating oncoming traffic is still flowing and has the right of way - as the oncoming lanes change to yellow then red, your left turn arrow will change to steady yellow arrow, then red arrow. at this point, if you are in the intersection awaiting your turn, you should be able to safely complete it and clear the intersection. assuming nobody in the oncoming lanes runs their red light, that is. - older installations may have a three-element signal, using a flashing red ball to indicate this. those are being replaced because they don’t clearly indicate when your left turn lane is about to change from “proceed if safe” to “stop.” ---
**Author:** ![Alley\_Dweller](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/alley_dweller/32/430_2.png) [@Alley\_Dweller](https://boards.straightdope.com/u/Alley_Dweller)\ **Post date:** [February 23, 2018, 5:34am UTC](https://boards.straightdope.com/t/traffic-light-question/809357/31 "2018-02-23T05:34:27Z")
By the way, this problem is why some cities in [Florida](http://www.nbc-2.com/story/22768557/good-question-what-are-those-blue-lights), [Minnesota](http://minnesota.cbslocal.com/2014/11/06/good-question-what-are-those-blue-traffic-lights/), and [Colorado](https://www.denverpost.com/2005/08/22/tattletale-devices-could-make-red-light-runners-blue/) have little blue lights next to their traffic signals. You can’t assume that the signal going in both directions is the same, so they have the little blue light attached to the signal turn on when the signal is red. That way, a police officer waiting at the far side of the intersection can tell when a driver went through the intersection on a red light. ---
**Author:** ![Dinsdale](https://avatars.discourse-cdn.com/v4/letter/d/97f17d/32.png) [@Dinsdale](https://boards.straightdope.com/u/Dinsdale)\ **Post date:** [February 23, 2018, 1:22pm UTC](https://boards.straightdope.com/t/traffic-light-question/809357/32 "2018-02-23T13:22:23Z")
> [@jz78817](#): > > Michigan. But I don’t think it’s done unless there’s also a left turn signal present. According to my wife, there were no turn signals. The road in question had 2 lanes of traffic in either direction. Not sure how many lanes the cross street had. Also, not sure whether there was a left turn lane. But no arrows on the stoplights. In a case where, say, W bound traffic has a longer green than E bound, do E,N, and S all wait while W continues. And then when W turns red, N and S get the green? Seems like it would work, but I had always assumed they turned red and green in pairs rather than asymmetrically. I guess any of the other folk wanting to turn right on red could… ---
**Author:** ![jz78817](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/jz78817/32/1028_2.png) [@jz78817](https://boards.straightdope.com/u/jz78817)\ **Post date:** [February 23, 2018, 3:02pm UTC](https://boards.straightdope.com/t/traffic-light-question/809357/33 "2018-02-23T15:02:36Z")
> [@Dinsdale](#): > > According to my wife, there were no turn signals. The road in question had 2 lanes of traffic in either direction. Not sure how many lanes the cross street had. Also, not sure whether there was a left turn lane. But no arrows on the stoplights. > > In a case where, say, W bound traffic has a longer green than E bound, do E,N, and S all wait while W continues. And then when W turns red, N and S get the green? Seems like it would work, but I had always assumed they turned red and green in pairs rather than asymmetrically. I guess any of the other folk wanting to turn right on red could… that sounds like a massive fail on the part of whoever set up the signaling. ---
**Author:** ![Gorsnak](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/gorsnak/32/7587_2.png) [@Gorsnak](https://boards.straightdope.com/u/Gorsnak)\ **Post date:** [February 23, 2018, 3:38pm UTC](https://boards.straightdope.com/t/traffic-light-question/809357/34 "2018-02-23T15:38:42Z")
I was recently in a somewhat similar accident in the role of the left-turner - except, I saw that the guy was going to run the light and stopped. Then the guy who was trying to sneak through the left behind me hit me from behind. The red-light runner was especially egregious, too. An oncoming big rig was just slowly pulling into the intersection when the light turned yellow, and it had turned red long before the semi cleared the intersection. I was rolling forward trying to time it so I would roll through the instant he was clear when I saw an SUV behind him looking like he might not stop. I said out loud to no one, “He isn’t actually going through, is he?” But he was, and I hit the brakes, and got clipped (very minor damage) from behind. To be fair to the guy trying to turn illegally behind me, it’s a horrible intersection for turning left. At that time of day unless there are enough cars to get an arrow (which there weren’t) you can only turn left on the yellow, and the light cycle seems like it’s about 5 minutes. ---
**Author:** ![kayaker](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/kayaker/32/441_2.png) [@kayaker](https://boards.straightdope.com/u/kayaker)\ **Post date:** [February 23, 2018, 4:59pm UTC](https://boards.straightdope.com/t/traffic-light-question/809357/35 "2018-02-23T16:59:36Z")
> [@Dinsdale](#): > > I’d imagine one MIGHT be able to call the village/state, and find out how they are controlled. If I were the driver being accused of running a red, I’d have come to the hearing with that information in hand. ---
**Author:** ![Dinsdale](https://avatars.discourse-cdn.com/v4/letter/d/97f17d/32.png) [@Dinsdale](https://boards.straightdope.com/u/Dinsdale)\ **Post date:** [February 23, 2018, 5:52pm UTC](https://boards.straightdope.com/t/traffic-light-question/809357/36 "2018-02-23T17:52:24Z")
> [@jz78817](#): > > that sounds like a massive fail on the part of whoever set up the signaling. I dunno, man. This was in a Chicago suburb, but in Chicago, there are any number of signal-controlled intersections where there are no designated turn lanes and no turn signal arrows. ---
**Author:** ![Horatius](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/horatius/32/3572_2.png) [@Horatius](https://boards.straightdope.com/u/Horatius)\ **Post date:** [February 23, 2018, 6:01pm UTC](https://boards.straightdope.com/t/traffic-light-question/809357/37 "2018-02-23T18:01:55Z")
> [@Barkis\_is\_Willin](#): > > If they don’t turn at the same time, there should be a lighted arrow and a left turn lane. When I’m in the position of the westbound driver, I make damn sure that eastbound traffic is stopping before I complete my turn. I figure north/south drivers are going to have to wait for me regardless. There are some jurisdictions that use a flashing green light as an indication that only that direction may proceed. Such a light setup is indistinguishable from a normally-switched light system, so only the drivers who can see the flashing green light would know they have the sole right of way at that moment. These are being phased out in favor of lights with arrows, but they still exist in several places I normally drive. ---
**Author:** ![jz78817](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/jz78817/32/1028_2.png) [@jz78817](https://boards.straightdope.com/u/jz78817)\ **Post date:** [February 23, 2018, 6:25pm UTC](https://boards.straightdope.com/t/traffic-light-question/809357/38 "2018-02-23T18:25:47Z")
> [@Dinsdale](#): > > I dunno, man. This was in a Chicago suburb, but in Chicago, there are any number of signal-controlled intersections where there are no designated turn lanes and no turn signal arrows. I’m talking about the longer green in one direction with no indication of such for the opposite direction. ---
**Author:** ![D\_Anconia](https://avatars.discourse-cdn.com/v4/letter/d/67e7ee/32.png) [@D\_Anconia](https://boards.straightdope.com/u/D_Anconia)\ **Post date:** [February 23, 2018, 7:23pm UTC](https://boards.straightdope.com/t/traffic-light-question/809357/39 "2018-02-23T19:23:43Z")
> [@Riemann](#): > > The law says you can (and should) enter the intersection and wait if the only thing preventing you from completing your left turn is oncoming traffic. That’s not true in every jurisdiction. > [@](#): > > Drivers entering an intersection to turn left: > 1.Can wait in the intersection until they can turn left. > 2.Must wait for the green arrow before turning left. > 3.Can wait in the intersection until the light turns yellow before turning left. > \*\*4.Must not enter an intersection unless they can get through it without having to stop. > > If you answered “D,” then you’re correct, according to DOL.\*\* [https://www.seattlepi.com/local/transportation/article/Getting-There-What-is-the-law-on-left-turns-3603191.php](https://www.seattlepi.com/local/transportation/article/Getting-There-What-is-the-law-on-left-turns-3603191.php) ---
**Author:** ![PoppaSan](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/poppasan/32/189_2.png) [@PoppaSan](https://boards.straightdope.com/u/PoppaSan)\ **Post date:** [February 24, 2018, 2:57am UTC](https://boards.straightdope.com/t/traffic-light-question/809357/40 "2018-02-24T02:57:02Z")
> [@Dinsdale](#): > > According to my wife, there were no turn signals. The road in question had 2 lanes of traffic in either direction. Not sure how many lanes the cross street had. Also, not sure whether there was a left turn lane. But no arrows on the stoplights. > > In a case where, say, W bound traffic has a longer green than E bound, do E,N, and S all wait while W continues. And then when W turns red, N and S get the green? Seems like it would work, but I had always assumed they turned red and green in pairs rather than asymmetrically. I guess any of the other folk wanting to turn right on red could… Yep, sounds about right. West gets a longer green than east while N & S twiddle their thumbs /check their email. > [@jz78817](#): > > that sounds like a massive fail on the part of whoever set up the signaling. I have several I routinely travel. Upon inspection, most seem to be along frontage road intersections near the on/off ramps of the freeway. The light taking traffic away from the ramps are green longer and timed a bit with the lights for the ramps. Appears to be used to clear traffic out of the area. [Previous page](https://boards.straightdope.com/t/traffic-light-question/809357.md?page=1) [Next page](https://boards.straightdope.com/t/traffic-light-question/809357.md?page=3)