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Seeing yellow
January 5, 2013 6:16 AM   Subscribe

THE PROBLEM OF THE AMBER SIGNAL LIGHT IN TRAFFIC FLOW (PDF), published in 1959, is the origin of the yellow interval duration equation for traffic lights. But in China, as of Tuesday, yellow lights are now considered functionally the same as red lights, prompting outcries in the local media that it is not only unfair, but actually violates Newton's First Law of Motion. It also violates the history of traffic lights...

Our system of traffic lights is often attributed to the prolific African-American inventor Garrett Morgan, but his 1923 patent didn't include a yellow light. Even before that, concerned policeman William Potts installed multicolored (red, amber, green) traffic signals at this intersection in Detroit in 1920, inspired by railroad signals.

The yellow light didn't become standard until the 1935 edition (page 71) of the Manual on Uniform Traffic Control Devices (which has its own history and evolution.)

While the precise timing of yellow lights is usually intended to prevent accidents, it's not unusual for that timing to be adjusted for profit.
posted by twoleftfeet (47 comments total) 16 users marked this as a favorite

 
So, China has become a small southern town speed trap?
posted by Thorzdad at 6:23 AM on January 5, 2013 [6 favorites]


Don't be an "Amber Gambler"!
posted by Artw at 6:30 AM on January 5, 2013 [3 favorites]


So, China has become a small southern town speed trap?
Oh god, whenever I leave Baton Rouge to visit my family in their really small-town area, it feels like the police spend all of their time & energy on speed traps and traffic cameras. So frustrating.
posted by Evernix at 6:33 AM on January 5, 2013


Professor Frink: "We studied the traffic patterns and found that drivers move the fastest through yellow lights. So now, we just have the red and yellow lights. N'hey."

[cut to Lenny, driving on the street. The light turns from red to yellow, and Lenny floors it]

They Saved Lisa's Brain - AABF18 - The Simpsons
posted by Fizz at 6:36 AM on January 5, 2013 [2 favorites]


I recall all the lights in New York City being just red and green, into the 1960s. Instead of amber, both lights would be on for a few seconds before red-only.
posted by beagle at 6:44 AM on January 5, 2013 [1 favorite]


Huh. It seems to me that many technologies work like this -- there is a new development that offers people a way to do something better (usually faster). It requires a certain amount of skill, knowledge, and attention to do well. In an effort to sell more access, people refine the technology to make the action require less skill, knowledge, and attention so that more people can do it. Of course, people who are driven by a profit motive don't really care that you do the thing or enjoy the thing; they just want you to pay them for the privilege. As problems mount, the government gets involved, first to deal with those problems and then to ensure a revenue stream from the activity.

It's all complicated because technology can't actually replace skill. As a librarian, I see this most immediately in search activities -- we are regularly offered "better search technologies" which really are just better at giving the searcher something (plus an add or a dollop of personal information to sell) rather than the best thing. Now, 9 times out of 10, that's good enough; if I am looking for the time for movies at the local theater, it doesn't really matter which site gives them to me. However, when I am in that 10th situation, the technology not only doesn't help, it actually obscures what I am doing, making it impossible for me to really do the search I want (assuming I don't have the skill and understanding to know what is going on and circumvent the helpful tool). The internet isn't getting better at letting you find information; it's getting better at selling you something and flattering you into thinking you found it. Similarly, half of the problems we have with traffic is because people can't be bothered to learn to drive and focus their attention on driving. So we end up with the situation in downtown Providence where a bunch of the lights go red both ways (apparently to avoid collisions when people run red lights). This results in oddly long periods when traffic is at a standstill with no one having any clear idea who is supposed to go and when. In further efforts to automate traffic flow, the city has installed lights that respond to stopped traffic, to allow busier streets to "run" longer. Except the system was put in place without taking into account the variety of vehicles (including delivery trucks and buses), and so the lights won't trigger properly, which has led to drivers treating stop lights downtown as stop signs, since, otherwise, they might sit there for 10 minutes waiting for a light to change. Walk lights that trigger only when buttons (often inconveniently located) are pressed often don't work at all, leading pedestrians to ignore traffic lights all together.

And so on. Instead of producing drivers, we focus on producing fool-proof systems, but, since the inventiveness of fools (especially smart fools) is inconceivable, the system is always losing the race. Add in gaming the system for a profit motive, and the most likely outcome is vastly increased difficulty of soing what the user is trying to do with less ability to actually do it.
posted by GenjiandProust at 6:59 AM on January 5, 2013 [10 favorites]


I thought in Communist countries that Red meant go.
posted by Renoroc at 6:59 AM on January 5, 2013


This has been my experience:

In New Zealand, GGGGGG-AAA-RRRRRR...

In Canada, GGGGGG-A-RRRRRR...

Let's just say that since living in Canada, I've gone through a lot of red lights.
posted by piyushnz at 7:01 AM on January 5, 2013


I couldn't find a reference, but most likely I read in Tom Vanderbilt’s excellent book Traffic, that at the time when traffic lights were just red and green, and they were discussing the possibility of introducing yellow, the main objection was that a yellow mode would just make motorists speed up to get through the intersection.

I've never done that. No. Not even once. I always brake at yellow. I'm a good citizen. Really.. I wouldn't need to justify it if it wasn't true, right?

The history of traffic is more interesting than it sounds. Did you know that the first Stop signs had black letters on a white background? I could talk about traffic signs all day, because they're that fascinating. And because I'm on a cross-country road trip, and there's nothing else to talk about.
posted by twoleftfeet at 7:02 AM on January 5, 2013 [1 favorite]


And because I'm on a cross-country road trip, and there's nothing else to talk about.

If you are posting this from your phone while driving, you are part of the problem, citizen!
posted by GenjiandProust at 7:08 AM on January 5, 2013 [2 favorites]


I look at what people are doing while they're driving, and half the time they are texting or checking voicemail or playing Angry Birds. We can't fight that, so we should find a way to control our automobiles with our iPhones, right?
posted by twoleftfeet at 7:19 AM on January 5, 2013 [1 favorite]


to be adjusted for profit.

Speeders and reckless drivers whine about big government just as much as Tea Party members.
posted by three blind mice at 7:21 AM on January 5, 2013 [7 favorites]


We can't fight that

We could remove the thumbs of people caught using their phones while driving. That would sort out some of the problems. (Note: I make no claims that my being given supreme executive authority would in any way be a good idea.)
posted by GenjiandProust at 7:24 AM on January 5, 2013 [1 favorite]


Other than government collecting more traffic violation money the only other people to benefit from this will be those in the auto body repair business. As the Washington Post article point out, "Given that motorists will often take just one or two short seconds to screech to a halt before crossing into a yellow light, more accidents seem likely."
posted by Slack-a-gogo at 7:35 AM on January 5, 2013


ah, welcome traffic nerds. A little more analysis:

Empirical studies indicate that longer yellow lights allow people more time to react to changing light cycles. Consequently, placing computerized, law enforcement devices at intersections with short yellow lights can obviously result in more red light citations than can computer–enforcement devices placed at intersections with longer yellow lights. It is the effect of the short yellow light on apparent red light running that the red light camera program in San Diego has seized upon in order to maximize revenue.

The reason why short yellow lights create a trap for people driving is that short yellow lights create an "impossible to stop" zone in which a certain percentage of people approaching an intersection become caught in the dilemma of not being able to stop safely before the light turns red, and not being able to cross into the intersection without technically running a red light. Federal traffic control standards require that a traffic control device give drivers adequate time for a proper response. Acceptable traffic engineering standards require that a yellow light be long enough to allow drivers sufficient time to stop their vehicle safely at the limit line before the traffic light changes from yellow to red. There are different methods of calculating appropriate yellow light time based on factors like road grade and approach speed. The recent traffic engineering practice has been to determine approach speed by using the posted speed limit rather than the 85th percentile speed (the speed at which 85 percent of people are thought to be driving). However, it is more appropriate to base these calculations on the speed at which people are actually driving toward the intersection. The faster the approach speed and the shorter the yellow light, the greater the likelihood that people driving will be caught in the "impossible to stop" zone and forced to run the red light.

Data from public records suggests that the operators of the red light camera program in San Diego exploited the "impossible to stop" zone by selecting intersections for computer–enforcement that have relatively high speeds and short yellow lights. This situation is not unlike the age–old law enforcement technique of "sitting–in" described in the "Selective Traffic Enforcement Manual" by the International Association of Chiefs of Police, Inc. (January 1972). The technique of "sitting–in" is explained in the manual’s introduction as follows:

Sitting–in usually occurs at locations which, in police jargon, are referred to as "duck ponds" or "cherry patches". The sitting–in practices are particularly objectionable when two or more enforcement units group together to work an intersection which generates frequent driver violations. Usually, where this situation occurs, the officers are doing nothing more than reaping the harvest of inadequate or poor traffic engineering. These locations frequently encourage noncompliance by the motorist to traffic signals or turning regulations. Very often, however, the real culprit is faulty traffic engineering rather than the driver. Poor positioning of signals and channelization deficiencies are characteristically present at the "duck ponds".

It appears that the red light camera program in San Diego is nothing more than a modern day, computerized version of the age–old law enforcement technique known as "sitting–in" where police officers seized on poor traffic engineering practices to ensure high citation rates. But, in this case, it isn’t police officers who are doing the "sitting–in" so much as it is the private company that operates the program. By placing cameras at intersections where drivers are actually forced to run the red lights due to seemingly poor traffic engineering practices, the company that operates the program ensured that the program would generate millions of dollars in revenue each year.

posted by wallstreet1929 at 7:35 AM on January 5, 2013 [31 favorites]


Speeders and reckless drivers whine about big government just as much as Tea Party members.

So you're saying that reducing yellow light times in an unsafe manner is just fine, and if you complain about it, you're just like those no-good Tea Party folks? OK then.
posted by zsazsa at 8:02 AM on January 5, 2013 [13 favorites]


Re: the "profit" link in the post - a several-years-old document on this issue in Baltimore. Some of it is laughable and might be good reading for folks who think privatization can cure all ills.
A couple of highlights:
There are frequent reports that yellow light times are inconsistent.  There are reports that yellow light time variations occur on the same light. A rough analysis of several citations issued in Baltimore City documented this phenomenon. 
  When being briefed on the RLCES, the Court was advised that the minimum speed threshold was to be 12 to 15 mph.  Therefore it was very surprising to see a number of the RLCES' minimum speed thresholds were set to 0 mph.  Also, two of the intersections have a minimum speed threshold of 25 or 35 mph.  When a follow-up question was posed to an ACS representative, the Court was told that the minimum speed threshold was 12 mph at the lowest.  When it was pointed out that the table illustrated over 16 intersections that had a threshold of 0 mph, the ACS representative requested where the Court had obtained this information and asked that it be faxed to ACS.  The Court then informed ACS that the information had been received from ACS.
    A defense often cited in court by someone who has received a red light citation is that he/she ran the light in order to prevent being hit from behind.  Data from the Final Report on the City of San Diego Photo Enforcement System concluded that although red light running did decrease as did intersectional accidents, those decrease were
outweighed by the 3% increase in rear end collisions occurring at red light camera intersections.
posted by zoinks at 8:20 AM on January 5, 2013 [4 favorites]


Also sort of tangentially related: the Barnes Dance.
posted by zoinks at 8:31 AM on January 5, 2013


The movie "Starman" describes what a visitor to Earth may conclude about the functional meaning of the red, yellow, and green lights...
posted by Schmucko at 8:33 AM on January 5, 2013 [4 favorites]


Just about nobody stops for yellow. Everywhere I have been in the US yellow lights are a fucking joke. Light turns yellow, people speed up. Watching a light turn red while a vehicle is still in the intersection does not require a short yellow or any kind of sneakiness. Just watch long enough at any intersection with a decent flow of traffic.
posted by idiopath at 8:43 AM on January 5, 2013 [1 favorite]


Schmucko, you beat me by that much!
posted by TedW at 8:43 AM on January 5, 2013 [1 favorite]


In BC we have mandatory basic insurance from ICBC, a provincial corporation. There are many benefits to this.

One is that ICBC runs the red light camera program. It's revenue neutral: the fines go toward maintenance, new cameras, and — importantly — redesign of high collision intersections.

One of the neat things about crown corporations is that we get to tell them what to do. "Fix bad intersections instead of profiting from them" is one example.
posted by five fresh fish at 8:48 AM on January 5, 2013 [15 favorites]


We studied the traffic patterns and found that drivers move the fastest through yellow lights.

Wow. That's some study. How much did that cost?
Now make yellow functionally the same as red and do another study.
Let me guess: Drivers move faster through green than previously.
posted by weapons-grade pandemonium at 8:48 AM on January 5, 2013


So you're saying that reducing yellow light times in an unsafe manner

You're begging the question. Whether the yellow lights have been reduced in an "unsafe manner" is really the issue. And the controversy (in the US anyway) revolves mostly around whether the yellow light timing is based off of the posted speed limit or the 85% speed. The yellow isn't impossibly short if you're going the speed limit. If you don't speed, there's no problem.
posted by Kadin2048 at 8:57 AM on January 5, 2013 [1 favorite]


So that means the Chinese will be ignoring the yellow lights as well as the reds?
posted by photoslob at 8:58 AM on January 5, 2013


my personal favorites are the german stoplights that go:

green: yellow: red: yellow: green

You get a nice warning that it's about to change to green, so people starting revving their engines and beeping their horns at you to go.
posted by readyfreddy at 8:59 AM on January 5, 2013


You get a nice warning that it's about to change to green

Which makes sense where most cars are manual transmission: it gives you time to bring the clutch up to biting point and get your hand on the handbrake ready to release it. (Maybe even to put it back into gear, if you've slipped it into neutral to give your clutch foot a rest.)

UK lights are similar: red / red-and-amber / green / amber / red -- except that the red-and-amber eliminates any ambiguity of "is it turning green or turning red?"

I was taught (in the UK) that both amber and red mean "stop if it is safe to do so"; although in practice it doesn't really work like that.
posted by We had a deal, Kyle at 9:12 AM on January 5, 2013 [1 favorite]


> If you don't speed, there's no problem.

Absolutely. And before the "but don't you care about saving (drivers) lives, it's better to design for what people are actually doing" argument, keeping drivers from speeding is a guaranteed way to make the streets safer for unprotected road users (pedestrians, cyclists, etc.).
posted by anthill at 9:15 AM on January 5, 2013 [2 favorites]


It strikes me--particularly since watching Ai Weiwei: Never Sorry (which I highly recommend)--how obvious this is, since the Chinese establishment has no 'yellow light'. Things are right or wrong / black or white, with no tolerance for shades of grey.
posted by weapons-grade pandemonium at 9:26 AM on January 5, 2013


If I were Traffic God, I'd keep the amber/red thing as is. That is, if you're in the intersection BEFORE the light goes red, you're good. If not, you're in contravention.

Except for anyone under say 27.

Younger drivers, sorry, you still don't have the judgment. You still rate the convenience of zooming/accelerating on through and getting home one minute earlier to masturbate (or whatever) as higher than the the convenience of NOT having a nasty accident.

At least, I sure did until I was say 27.

And don't kid yourself, the enthusiastic running of amber lights rates very high in the the causation of nasty accidents. It's the guy trying to make the left turn across your lane. He's been hung out waiting there since the light went green for him. He sees the amber, he reads it as his time to finally move. Unless he's paying very close attention to what oncoming idiot (ie: you) is doing, unless he reads that oncoming idiot has no intention of stopping, in fact is about to nail the gas, accelerate on through ... well, the rest is like an extremely troubling JG Ballard novel.
posted by philip-random at 9:33 AM on January 5, 2013


The yellow isn't impossibly short if you're going the speed limit. If you don't speed, there's no problem.
But another problem is that some places make the yellow too short even for non-speeders. Not meaning to excuse the many many folks who are speeding through lights at or past the last moment of course.
posted by zoinks at 9:41 AM on January 5, 2013 [1 favorite]


You're begging the question. Whether the yellow lights have been reduced in an "unsafe manner" is really the issue. And the controversy (in the US anyway) revolves mostly around whether the yellow light timing is based off of the posted speed limit or the 85% speed. The yellow isn't impossibly short if you're going the speed limit. If you don't speed, there's no problem.--Kadin2048

No. Maybe you don't know what has happened in a number of cities. These cameras are expensive. One of the camera companies made a deal with cities to reduce the yellow time so that it is impossibly short, guaranteeing a number of violations (usually at least one per light change), so the city would get revenue to help pay for the cameras.

There were various lawsuits where evidence of this came out, along with evidence of increased accidents and even more traffic deaths. The cities (including Cupertino, California near where I live), where forced to shut down the cameras at great cost.
posted by eye of newt at 9:43 AM on January 5, 2013 [3 favorites]


I've always liked the lights that have the digital countdown to the light changing. I've seen them in a few countries, including China and thought they were an excellent way of determining if it were safe to move into the intersection. You'll still get idiots, and the penalties should be stinging to dissuade people from chancing it.

Also, does no-one else check what the crosswalk signals are doing? When the hand starts flashing here in Canada to warn the pedestrians, it's a sign that the light is about to change against you so you might as well start preparing to stop.
posted by arcticseal at 9:45 AM on January 5, 2013 [2 favorites]


I like how in Mexico before turning yellow the green light will flash a few times and then turn yellow. It is sort of a warning the light is about to change. Of course to many taxistas it means floor it.
posted by birdherder at 9:46 AM on January 5, 2013 [3 favorites]


When the hand starts flashing here in Canada to warn the pedestrians, it's a sign that the light is about to change against you so you might as well start preparing to stop.

Not always.
posted by one more dead town's last parade at 9:47 AM on January 5, 2013


And the controversy (in the US anyway) revolves mostly around whether the yellow light timing is based off of the posted speed limit or the 85% speed. The yellow isn't impossibly short if you're going the speed limit. If you don't speed, there's no problem.--Kadin2048

Judging by the yellow light duration formula above, none of the traffic lights here in Tuscaloosa are safe. The longest yellow light I see is 3 seconds, and that's on a 65mph highway where the 85% speed is more like 75mph. State law has recently been amended to allow red light cameras, and the city is studying which intersections to install cameras at. The only mention of yellow light duration was a recommendation by the city traffic engineer to suggest that yellow lights at camera intersections be increased from 2 seconds to 3. They may not be impossibly short, but the lights here are generally dangerously short.
posted by fogovonslack at 11:51 AM on January 5, 2013


Not always.

Thanks, always pays to pay attention. YLightMV.
posted by arcticseal at 12:15 PM on January 5, 2013 [1 favorite]


Longstanding law in Virginia makes it illegal to enter an intersection on either yellow or red. On yellow it is legal to proceed through an intersection you entered when the light was green.
posted by NortonDC at 12:52 PM on January 5, 2013 [1 favorite]


Just about nobody stops for yellow. Everywhere I have been in the US yellow lights are a fucking joke. Light turns yellow, people speed up.

The people closest to the intersection, sure. Uh, not the people farther back on the road, though.
posted by desuetude at 12:55 PM on January 5, 2013


When I first moved to America I would sometimes stop at a red light and then not notice the change to green til someone honked.

Eventually I realized that my London-trained brain was used to day-dreaming at stoplights, and waking up on yellow, but the US lights went straight from red to green.
posted by w0mbat at 1:00 PM on January 5, 2013 [1 favorite]


Longstanding law in Virginia makes it illegal to enter an intersection on either yellow or red.
"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, but traffic which has already entered the intersection shall continue to move until the intersection has been cleared."
Not quite the same as "it's illegal to enter an intersection on yellow".
posted by Lazlo Nibble at 1:10 PM on January 5, 2013 [2 favorites]


Yes, Lazlo, there is an out to avoid legislating unsafe stops, yet the law otherwise prohibits entering the intersection on yellow.
posted by NortonDC at 4:40 PM on January 5, 2013


In Australia, an amber light has always compelled drivers to stop if you can stop safely. (linking to just one state's rules, but they're all the same iirc). I suspect most people don't know of this, though.

A policeman can issue you a summons if he sees you are able to stop, but decide not to and just drive through a yellow. This can happen, say, if you're doing 20kmph in a 80kmph road, and the lights thus have a long amber period, you see them turn amber but you know it's a 3 second amber and just cruise through.

The rule of "you can't pass through on a red" I think is more applicable for traffic light cameras, because they are unable to judge if the driver was able to stop safely or not, and hence will never penalize someone for passing through on an amber even though it could technically be illegal depending on the circumstance.
posted by xdvesper at 4:56 PM on January 5, 2013


arcticseal writes "Also, does no-one else check what the crosswalk signals are doing? When the hand starts flashing here in Canada to warn the pedestrians, it's a sign that the light is about to change against you so you might as well start preparing to stop."

How accurate this is depends on the width of the intersection and the age profile of the crossing users (crossing lights in areas with a large proportion of seniors or disabled people have shorter Walk duration signals). One of the crossing signals outside the local hospital that crosses 5 lanes flashes over practically immediately.
posted by Mitheral at 5:18 PM on January 5, 2013


This change will make little difference because the number of traffic police in in this city will never keep pace with the number of new car owners. When I lived in America no matter how short a distance I drove, I saw at least one cop; in Beijing, I commute across the city twice daily and see a cop about twice a year. I predict nothing will change until we have permanent gridlock.
posted by wobumingbai at 6:58 AM on January 6, 2013


NortonDC: "Longstanding law in Virginia makes it illegal to enter an intersection on either yellow or red. On yellow it is legal to proceed through an intersection you entered when the light was green."

Those laws are there in most states. Nobody follows them.
posted by idiopath at 8:17 AM on January 6, 2013


Looks like the Chinese government is backing down on this. Hope they're still chasing the drunk driving though, it was endemic when I was living there.
posted by arcticseal at 9:40 AM on January 6, 2013


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