# Those traffic light grills are dangerous **URL:** \ **Category:** In My Humble Opinion\ **Created:** [August 15, 2011, 6:48pm UTC](https://boards.straightdope.com/t/those-traffic-light-grills-are-dangerous/592810 "2011-08-15T18:48:47Z")\ **Posts on this page:** 20\ **Page:** 1
**Author:** ![snailboy](https://avatars.discourse-cdn.com/v4/letter/s/97f17d/32.png) [@snailboy](https://boards.straightdope.com/u/snailboy)\ **Post date:** [August 15, 2011, 6:48pm UTC](https://boards.straightdope.com/t/those-traffic-light-grills-are-dangerous/592810/1 "2011-08-15T18:48:47Z")
For those who don’t know what I’m talking about or don’t have them in their area, I’ll explain. It’s basically a grill shaped like a honeycomb that covers the traffic light (usually just the green light) at an intersection so you can only see it when you’re about to enter the intersection. I have no idea what purpose they serve and always thuoght they were dangerous because it trains you to assume the light is green if you can’t see it when it could be unpowered. If you’re approaching an intersection and can’t see the light, it’s almost always because of these grills. It screwed me up today. I just exited the freeway onto the frontage road and was turning left. There were two left-turn lanes and the one to the right (which was a turn-optional lane) only had one car stopped at the line so I get in it. I can’t see any color of light but just as I’m pulling up, the cars at the front of the line start moving so I assumed it was green and followed. Upon entering the intersection, I realized the lights weren’t working at all but it was too late. Luckily I made it through okay, but I looked like some asshole who couldn’t be bothered to wait my turn. A crash could have occurred. So thanks state of Texas for actively making the streets more dangerous. ---
**Author:** ![purplehorseshoe](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/purplehorseshoe/32/2996_2.png) [@purplehorseshoe](https://boards.straightdope.com/u/purplehorseshoe)\ **Post date:** [August 15, 2011, 7:00pm UTC](https://boards.straightdope.com/t/those-traffic-light-grills-are-dangerous/592810/2 "2011-08-15T19:00:56Z")
I live in Dallas, and I wholeheartedly _thumbs up_ this rant. I hate those things, and don’t understand their purpose AT ALL. ---
**Author:** ![gotpasswords](https://avatars.discourse-cdn.com/v4/letter/g/c57346/32.png) [@gotpasswords](https://boards.straightdope.com/u/gotpasswords)\ **Post date:** [August 15, 2011, 7:02pm UTC](https://boards.straightdope.com/t/those-traffic-light-grills-are-dangerous/592810/3 "2011-08-15T19:02:02Z")
> [@](#): > > … it trains you to assume the light is green if you can’t see it when it could be unpowered. And there’s your problem. If you can’t see the light, you are obligated to assume the signals are out and treat it as an all-way stop. ---
**Author:** ![snailboy](https://avatars.discourse-cdn.com/v4/letter/s/97f17d/32.png) [@snailboy](https://boards.straightdope.com/u/snailboy)\ **Post date:** [August 15, 2011, 7:07pm UTC](https://boards.straightdope.com/t/those-traffic-light-grills-are-dangerous/592810/4 "2011-08-15T19:07:42Z")
> [@gotpasswords](#): > > And there’s your problem. > > If you can’t see the light, you are obligated to assume the signals are out and treat it as an all-way stop. That’d be the better thing to do, but when it’s those grills 99% of the time, you get so used to it you assume it without even really thinking about it. ---
**Author:** ![running\_coach](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/running_coach/32/15836_2.png) [@running\_coach](https://boards.straightdope.com/u/running_coach)\ **Post date:** [August 15, 2011, 7:12pm UTC](https://boards.straightdope.com/t/those-traffic-light-grills-are-dangerous/592810/5 "2011-08-15T19:12:52Z")
The purpose is that each lane can only see their light and not be confused by others. ---
**Author:** ![purplehorseshoe](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/purplehorseshoe/32/2996_2.png) [@purplehorseshoe](https://boards.straightdope.com/u/purplehorseshoe)\ **Post date:** [August 15, 2011, 7:18pm UTC](https://boards.straightdope.com/t/those-traffic-light-grills-are-dangerous/592810/6 "2011-08-15T19:18:52Z")
> [@gotpasswords](#): > > And there’s your problem. > > If you can’t see the light, you are obligated to assume the signals are out and treat it as an all-way stop. Ha. Come to Dallas. Slow to a crawl as you approach each major intersection. (Mind you, some of these, you can’t see the light until you’re two freet from the crosswalk.) Lemme know how many times you get rear-ended in the space of, oh, fifteen minutes. :rolleyes: > [@runner pat](#): > > The purpose is that each lane can only see their light and not be confused by others. How the fuck would a semi-intelligent person get “confused” by traffic lights _facing a different direction_? I mean, I know they hand out drivers licences like candy and all, but … is it facing you? Yes? Then it’s meant for you! Facing the side? Not for you, skipper! ---
**Author:** ![voltaire](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/voltaire/32/313_2.png) [@voltaire](https://boards.straightdope.com/u/voltaire)\ **Post date:** [August 15, 2011, 7:18pm UTC](https://boards.straightdope.com/t/those-traffic-light-grills-are-dangerous/592810/7 "2011-08-15T19:18:57Z")
Have you ever seen someone waiting at a light to go straight, and when the left-turn signal turns to green they see it and instinctively drive out into the intersection even though their light to go straight is still red? That’s the intended purpose - so that the lights are only readily visible to the lanes that they pertain to. That said, I’m glad they don’t have those where I live. It seems they cause more problems than they fix. ---
**Author:** ![running\_coach](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/running_coach/32/15836_2.png) [@running\_coach](https://boards.straightdope.com/u/running_coach)\ **Post date:** [August 15, 2011, 7:25pm UTC](https://boards.straightdope.com/t/those-traffic-light-grills-are-dangerous/592810/8 "2011-08-15T19:25:27Z")
> [@purplehorseshoe](#): > > How the fuck would a semi-intelligent person get “confused” by traffic lights _facing a different direction_? I mean, I know they hand out drivers licences like candy and all, but … is it facing you? Yes? Then it’s meant for you! Facing the side? Not for you, skipper! Some intersections have a separate set of lights for the turn lane. ---
**Author:** ![snailboy](https://avatars.discourse-cdn.com/v4/letter/s/97f17d/32.png) [@snailboy](https://boards.straightdope.com/u/snailboy)\ **Post date:** [August 15, 2011, 7:35pm UTC](https://boards.straightdope.com/t/those-traffic-light-grills-are-dangerous/592810/9 "2011-08-15T19:35:39Z")
(With a little more searching, it seems they’re called louvres (makes sense) so that’s what I’m going to call them from now on.) > [@runner pat](#): > > The purpose is that each lane can only see their light and not be confused by others. Then why not make them vertical bars so you can actually see them before you get right up to the intersection? > [@runner pat](#): > > Some intersections have a separate set of lights for the turn lane. Those lights have green arrows too instead of a green circle. It’s hard to get them confused. ---
**Author:** ![beowulff](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/beowulff/32/542_2.png) [@beowulff](https://boards.straightdope.com/u/beowulff)\ **Post date:** [August 15, 2011, 7:43pm UTC](https://boards.straightdope.com/t/those-traffic-light-grills-are-dangerous/592810/10 "2011-08-15T19:43:10Z")
The louvers aren’t there to prevent confusion - they are there to prevent people from anticipating the light change, by looking at the color of the light in other lanes, or to prevent people from blowing through a green light. The traffic engineers WANT you to not be able to see the color of the light until you are right next to it. ---
**Author:** ![snailboy](https://avatars.discourse-cdn.com/v4/letter/s/97f17d/32.png) [@snailboy](https://boards.straightdope.com/u/snailboy)\ **Post date:** [August 15, 2011, 7:55pm UTC](https://boards.straightdope.com/t/those-traffic-light-grills-are-dangerous/592810/11 "2011-08-15T19:55:06Z")
> [@beowulff](#): > > The louvers aren’t there to prevent confusion - they are there to prevent people from anticipating the light change, by looking at the color of the light in other lanes, or to prevent people from blowing through a green light. The traffic engineers WANT you to not be able to see the color of the light until you are right next to it. I’m not sure how either of those are worse than training people that if you can’t see the light, it’s green. ---
**Author:** ![cjepson](https://avatars.discourse-cdn.com/v4/letter/c/a9adbd/32.png) [@cjepson](https://boards.straightdope.com/u/cjepson)\ **Post date:** [August 15, 2011, 8:01pm UTC](https://boards.straightdope.com/t/those-traffic-light-grills-are-dangerous/592810/12 "2011-08-15T20:01:26Z")
> [@beowulff](#): > > The louvers aren’t there to prevent confusion - they are there to prevent people from anticipating the light change, by looking at the color of the light in other lanes, or to prevent people from blowing through a green light. The traffic engineers WANT you to not be able to see the color of the light until you are right next to it. Most of the time I’m OK with louvers. There is one intersection not far from where I live, however, where the light is at the end of a gentle curve, so that if you’re going the speed limit, you can’t see what color the light is until you’re too close to stop in time if it’s red. So basically the light is a permanent traffic hazard placed there by the authorities that requires you to slow way down when approaching the intersection. (Or that’s how it should work… actually, most people don’t slow way down, but make an inference on what color the light will be when they get to it based on what all the other traffic is doing. So if you do slow way down, you might get rear-ended. It’s just a veritable circus of fun and excitement all round.) ---
**Author:** ![Bosstone](https://avatars.discourse-cdn.com/v4/letter/b/22d042/32.png) [@Bosstone](https://boards.straightdope.com/u/Bosstone)\ **Post date:** [August 15, 2011, 8:12pm UTC](https://boards.straightdope.com/t/those-traffic-light-grills-are-dangerous/592810/13 "2011-08-15T20:12:11Z")
> [@beowulff](#): > > The louvers aren’t there to prevent confusion - they are there to prevent people from anticipating the light change, by looking at the color of the light in other lanes, or to prevent people from blowing through a green light. The traffic engineers WANT you to not be able to see the color of the light until you are right next to it. I WISH more people would look at other lanes. The problem in Phoenix isn’t people jumping the gun, it’s people not freaking paying attention. I’d love it if they were looking at the cross streets and checking the lights and looking for cars coming rather than sit like lumps for 10 seconds after the light goes green. ---
**Author:** ![divemaster](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/divemaster/32/78_2.png) [@divemaster](https://boards.straightdope.com/u/divemaster)\ **Post date:** [August 15, 2011, 8:30pm UTC](https://boards.straightdope.com/t/those-traffic-light-grills-are-dangerous/592810/14 "2011-08-15T20:30:33Z")
> [@voltaire](#): > > Have you ever seen someone waiting at a light to go straight, and when the left-turn signal turns to green they see it and instinctively drive out into the intersection even though their light to go straight is still red? No. I’ve seen a slight bump forward as the person releases the brake for a moment, but I’ve never seen anyone cruise the intersection under these circumstances. Maybe because over 80% of the intersections around here have separate cycles for the turn and straight lanes. People are used to it. Turn lanes first, THEN straight lanes. ---
**Author:** ![beowulff](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/beowulff/32/542_2.png) [@beowulff](https://boards.straightdope.com/u/beowulff)\ **Post date:** [August 15, 2011, 10:05pm UTC](https://boards.straightdope.com/t/those-traffic-light-grills-are-dangerous/592810/15 "2011-08-15T22:05:18Z")
> [@voltaire](#): > > Have you ever seen someone waiting at a light to go straight, and when the left-turn signal turns to green they see it and instinctively drive out into the intersection even though their light to go straight is still red? That’s the intended purpose - so that the lights are only readily visible to the lanes that they pertain to. > > That said, I’m glad they don’t have those where I live. It seems they cause more problems than they fix. I saw it today. The guy almost got T-boned by the oncoming traffic turning left into the intersection. He woke up and backed out of the intersection before getting smashed. ---
**Author:** ![Yllaria](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/yllaria/32/3452_2.png) [@Yllaria](https://boards.straightdope.com/u/Yllaria)\ **Post date:** [August 15, 2011, 10:14pm UTC](https://boards.straightdope.com/t/those-traffic-light-grills-are-dangerous/592810/16 "2011-08-15T22:14:15Z")
> [@beowulff](#): > > The louvers aren’t there to prevent confusion - they are there to prevent people from anticipating the light change, by looking at the color of the light in other lanes, or to prevent people from blowing through a green light. The traffic engineers WANT you to not be able to see the color of the light until you are right next to it. That’s not recommended by any Traffic Agency that I know of. > [@runner pat](#): > > The purpose is that each lane can only see their light and not be confused by others. The FHWA agrees. From [http://safety.fhwa.dot.gov/intersection/redlight/cameras/rlr\_report/chap3.cfm](http://safety.fhwa.dot.gov/intersection/redlight/cameras/rlr_report/chap3.cfm) > [@](#): > > Louvers are used to avoid confusion on intersection approaches where approaching motorists may be able to see the signal indication for another approach, typically due to a skewed approach angle at the intersection. Connecticut has a document showing when louvers should be used, with figures showing intersection angles. It’s the second one down [here](http://search.usa.gov/search?affiliate=CT.gov&v%3Aproject=firstgov&CATEGORIES_ID=0&query=louver). (It’s a pdf and their site truncates the address so I can’t link directly.) That’s the most common reason. Apparently there’s also something called Dallas Phasing [(see numbers 17 and 18)](http://midimagic.sgc-hosting.com/lturns.htm) that was allowed in the 2003 MUTCD\* to prevent [Yellow Trap](http://midimagic.sgc-hosting.com/lagtrpqz.htm)for certain kinds of split phasing patterns. It was forbidden in the 2009 MUTCD due to implementation problems. Dallas was allowed to leave old signals “in operation until replaced.” Even in Dallas Phasing, the louvers are supposed to keep through traffic from seeing the left turn signals. If the louvers are shortening the sight distance in the lane the signal is regulating THAT IS A SAFETY HAZARD and should be corrected. Write to complain. Get other people to write and complain. If you’re lucky, it will just be a matter of adjusting the louvers. But depending on the situation, the fix may require re-engineering and re-constructing the signal layout, which would not be cheap. So the more complaints, the more likely it will be fixed. - Manual on Uniform Traffic Control Devices (Most state require traffic signs, striping, and signals to conform to this manual. California has a modified version.) ---
**Author:** ![John\_DiFool](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/john_difool/32/19543_2.png) [@John\_DiFool](https://boards.straightdope.com/u/John_DiFool)\ **Post date:** [August 15, 2011, 10:56pm UTC](https://boards.straightdope.com/t/those-traffic-light-grills-are-dangerous/592810/17 "2011-08-15T22:56:05Z")
> [@beowulff](#): > > The louvers aren’t there to prevent confusion - they are there to prevent people from anticipating the light change, by looking at the color of the light in other lanes, or to prevent people from blowing through a green light. The traffic engineers WANT you to not be able to see the color of the light until you are right next to it. Then I guess places like Switzerland which have leading red/amber signals before the green, telling you that it’s about to change, are doing it wrong. I WANT to know what the other signals are doing (or about to do). ---
**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:** [August 15, 2011, 11:22pm UTC](https://boards.straightdope.com/t/those-traffic-light-grills-are-dangerous/592810/18 "2011-08-15T23:22:42Z")
For a while, [optically programmable signals](http://en.wikipedia.org/wiki/3M_High_Visibility_Signals) were popular for things like this, rather than louvers. basically you have the (high-output) bulb, lens, diffuser, and filter, and you could cover parts of the diffuser with opaque tape to control how much of the light could be seen off-axis. Unfortunately they cost like ten times what a normal traffic signal costs, so I haven’t seen any new ones go up since the '80s. ---
**Author:** ![thelabdude](https://avatars.discourse-cdn.com/v4/letter/t/dc4da7/32.png) [@thelabdude](https://boards.straightdope.com/u/thelabdude)\ **Post date:** [August 15, 2011, 11:32pm UTC](https://boards.straightdope.com/t/those-traffic-light-grills-are-dangerous/592810/19 "2011-08-15T23:32:54Z")
> [@Bosstone](#): > > I WISH more people would look at other lanes. The problem in Phoenix isn’t people jumping the gun, it’s people not freaking paying attention. I’d love it if they were looking at the cross streets and checking the lights and looking for cars coming rather than sit like lumps for 10 seconds after the light goes green. Very good point. ---
**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:** [August 15, 2011, 11:50pm UTC](https://boards.straightdope.com/t/those-traffic-light-grills-are-dangerous/592810/20 "2011-08-15T23:50:35Z")
> [@purplehorseshoe](#): > > How the fuck would a semi-intelligent person get “confused” by traffic lights _facing a different direction_? I mean, I know they hand out drivers licences like candy and all, but … is it facing you? Yes? Then it’s meant for you! Facing the side? Not for you, skipper! not all intersections meet at a 90° angle. [like so.](http://maps.google.com/?ll=42.471005,-82.986367&spn=0.007993,0.020213&z=16&vpsrc=6) [Next page](https://boards.straightdope.com/t/those-traffic-light-grills-are-dangerous/592810.md?page=2)