Traffic Waves
November 16, 2013 4:44 PM   Subscribe

Lewis Lehe created an interactive graphic that shows what happens when one driver brakes in traffic
posted by reenum (65 comments total) 18 users marked this as a favorite

 
Ugh, it felt like being in traffic. Which, I guess, means he did a good job.
posted by _paegan_ at 4:57 PM on November 16, 2013 [1 favorite]


Really neat.
posted by painquale at 5:00 PM on November 16, 2013


Yes, thank you very much, this is what happens when you dive into my barely moving line because you can't wait for yours to start moving again.
I can't wait for the day when everyone rides in an automated car. My life's anger index will drop to nearly zero and i will have more time to read.
posted by OHenryPacey at 5:07 PM on November 16, 2013 [12 favorites]


The solution is clear: brakes must be made illegal. Cars only need one pedal, an accelerator. They should always go faster, not slower.
posted by charlie don't surf at 5:09 PM on November 16, 2013 [3 favorites]


Now what are these brilliant traffic engineers doing to fix it? Can we get sorted speed lanes now, where people driving slower actually stay to the right?

Also, there are a few blind spots on 280 that cause these sorts of perturbations all the time. Could someone please trim the shrubbery?
posted by cman at 5:10 PM on November 16, 2013


And this is why I am constantly hissing "you are braking for no reason, and that makes you the cause of all this traffic," at the many terrible drivers on LA's freeways.
posted by yasaman at 5:12 PM on November 16, 2013 [8 favorites]


Of course the example photo of traffic is in Ontario.
posted by one more dead town's last parade at 5:13 PM on November 16, 2013 [4 favorites]


Leave it running for a few (15?) minutes and a traffic wave will form all on its own... Presumably not for any deep reason, but rather because of the floating-point arithmetic involved.
posted by jepler at 5:23 PM on November 16, 2013 [6 favorites]


Remember in MI3, when Tom Cruise' cover is working at the DoT and it's supposed to be funny how his cover character gets enthused at a party explaining how "traffic has a memory"?

Movie lost me right there because holy crap, pause the spy stuff, traffic has a memory.

This is a cool infographic.
posted by postcommunism at 5:26 PM on November 16, 2013 [2 favorites]


> Leave it running for a few (15?) minutes and a traffic wave will form all on its own...

Japanese experiment IRL showing just that.
posted by postcommunism at 5:29 PM on November 16, 2013 [5 favorites]


Can we get sorted speed lanes now, where people driving slower actually stay to the right?

Isn't that more of a driver education and enforcement issue? I've driven in countries like Germany where everyone actually follows the rules including proper use of passing lanes. You wouldn't believe how much easier driving is this way.
posted by JoeZydeco at 5:32 PM on November 16, 2013 [4 favorites]


There used to be signs here (MA) that said KEEP RIGHT EXCEPT TO PASS. They went away for some reason not explained to us. Lately, the following message has been sporadically appearing on those Amber Alert digital signboards: TRAVEL IN LEFT LANE PERMITTED ONLY WHEN PASSING. Some person thinks this is an improvement on the old signs. That person has the wrong job.

I find that, even in fairly heavy traffic, and even following the car ahead at three car lengths or less, I seldom have to brake when that car's brake lights come on. Maybe 20% of the time. The rest of the time, just lifting my foot off the gas slows me down enough to not get too close. Sometimes, I don't even have to lift my foot.

The people who really bother me are the ones who hit the brakes even though no one in their lane is braking, because people in some other lane are braking. I wish that they would not do that.
posted by Kirth Gerson at 5:48 PM on November 16, 2013 [5 favorites]


One of many reasons why our cars should primarily be driven by AI and not humans.
posted by Foci for Analysis at 5:55 PM on November 16, 2013 [3 favorites]


Could someone please trim the shrubbery?

You don't know me well enough to ask me that question, cman. You should at least buy me dinner and a movie first.
posted by ZenMasterThis at 5:56 PM on November 16, 2013 [1 favorite]


One of many reasons why our cars should primarily be driven by AI and not humans.

As someone who actively enjoys driving (at least, when not stuck in rush-hour/slow or jammed traffic), I'm not fully on board with this idea. But if we can get all the people who don't enjoy driving or aren't good at it to convert to AI-controlled vehicles, I think the rest of us would be happy to encourage them to do so while we go on our merry way.
posted by Greg_Ace at 6:04 PM on November 16, 2013


If you ride the break, eventually you'll break the program such that two cars can travel on top of each other, they can accelerate back to their normal speed and never be in an accident again. Now I've got a new trick to get through my next traffic jam!
posted by Nanukthedog at 6:31 PM on November 16, 2013


"Isn't that more of a driver education and enforcement issue? I've driven in countries like Germany where everyone actually follows the rules including proper use of passing lanes. You wouldn't believe how much easier driving is this way."

Freaking nobody understands or follows this rule, and this has been true my entire driving life, since 1980. It's an important safety rule, though most don't understand that. But what really rankles are the moderately high traffic four-lane highways/interstates where it's not necessary for traffic to be divided between both lanes but where such an indifference creates entirely needless bottlenecks.

"But if we can get all the people who don't enjoy driving or aren't good at it to convert to AI-controlled vehicles, I think the rest of us would be happy to encourage them to do so while we go on our merry way."

Self-driving cars will be (are) better drivers than the best of us, even and especially under congested conditions. If all or almost all cars are self-driving, you could immediately double the amount of traffic on current roads while still reducing the incidence of accidents.

I say this as a well-trained and experienced driver who was taught to take my vehicles near the extremes of their performance envelopes under controlled conditions, and to practice, so that I had the skill and knowledge to avoid collisions or reduce their severity in difficult circumstances. I did this for many, many years, mostly just for the love of driving.

At the advent of widespread self-driving cars, I'll probably pine for the good old days as deeply as anyone, but I don't delude myself that most collisions are the result of human error that even a dumb autopilot would have avoided.

If you look at the surveys of passenger air crashes you see that human error is by far the most common cause, with equipment failure in a distant second. And so many of those pilot errors are just dumb. These are former fighter jet pilots with thousands of hours in numerous aircraft who fly their planes into the ground while they fumble around checking to see if an indicator bulb is burned out.

It's not about skill and experience. I mean, it's even worse without skill and experience, of course. But while an autopilot may never be able to force a controlled oversteer on a curve on ice, sliding between two out-of-control vehicles, they will never fall asleep from fatigue because I work the overnight shift and drive home on a lonely highway for a half-hour at six in the morning six days a week.
posted by Ivan Fyodorovich at 6:35 PM on November 16, 2013 [6 favorites]


hit the brakes even though no one in their lane is braking, because people in some other lane are braking.

Other people braking could be a sign of some road hazard that they see and you do not. Or, when traffic in an adjacent lane changes, another driver could be planning to swerve out of that lane into your still-fast-moving one. Or they could be slowing down for no reason, but I'm not about to bet my life on it.
posted by Wulfhere at 6:40 PM on November 16, 2013 [4 favorites]


Of course the example photo of traffic is in Ontario.

The 401 is a special kind of hell.
posted by davebush at 6:50 PM on November 16, 2013 [1 favorite]


because of the floating-point arithmetic involved.

In firefox at least, if you keep hitting the brakes, it breaks the graphic, which is pretty neat. Other than that, this just makes me sad.
posted by Benway at 6:59 PM on November 16, 2013


YMMV.

(See what I did there?)
posted by ZenMasterThis at 7:08 PM on November 16, 2013 [1 favorite]


Isn't that more of a driver education and enforcement issue? I've driven in countries like Germany where everyone actually follows the rules including proper use of passing lanes. You wouldn't believe how much easier driving is this way.

Where there are posted speed limits in Germany, do people also refrain from exceeding that speed limit when passing, or forgo passing altogether if the car in front of them is already doing the speed limit?

I know always keeping right is the safe/correct thing to do, but I really don't support the left lane as a wide-open douchbag express corridor.
posted by RonButNotStupid at 7:21 PM on November 16, 2013


So, basically, the act of weaving from lane to lane to get another 50 meters ahead really slows things down for everybody else behind you?
posted by cacofonie at 7:26 PM on November 16, 2013 [1 favorite]


Of course the example photo of traffic is in Ontario.

More pointedly, it's the Pickering bottleneck, the absolute worst part of the eastbound 401. The 401 gets a bunch of traffic coming in from Sheppard and Whites Ave just before that rail bridge, then it narrows from 12 lanes to 10 a little bit beyond that rail bridge, and right after that there's more traffic pouring in (and trying in vain to pour out) at Brock Rd. It always jams up right there. Always. It can't not.
posted by Sys Rq at 7:28 PM on November 16, 2013


A sort-of opposite effect happens when people are exiting a building where there is a fire. The easy difference is that traffic is dangerous in front of you but fire is dangerous behind you.

Interestingly and sometimes tragically more numerous smaller exits result in a more orderly evacuation in an emergency even when the more numerous and smaller exits have less capacity [think surface area] than a lesser number of larger exits. Damned [I tried for an hour] if I can find the study or animation though.

It's an interesting subect.
posted by vapidave at 7:31 PM on November 16, 2013


"So, basically, the act of weaving from lane to lane to get another 50 meters ahead really slows things down for everybody else behind you?"

That's the best case scenario, as opposed to people just driving in one or the other lane for no good reason at all.

There's intuition that lane-neutral passing should be faster, or at worst no slower, than lane-biased passing, but that's not true. I worked this all out many years ago, but I've forgotten the details. I think it involves the asymmetry allowing a decidable sorting rule which the symmetric version lacks.
posted by Ivan Fyodorovich at 7:43 PM on November 16, 2013


Of course the example photo of traffic is in Ontario.

The 401 is a special kind of hell.
I contend that the Don Valley Parkinglot is part of that hell. It's a very explicit demonstration of this traffic wave concept as well: if just a few vehicles struggle up that hill going north near York Mills, some cars behind them will brake and the cars behind them.. and lo and behold, you'll end up with a four kilometre standstill going back to Eglinton Avenue. I don't even want to think how many minutes of people's lives in aggregate are wasted every year because of this landscape "feature".
posted by tksh at 7:44 PM on November 16, 2013 [1 favorite]


But if we can get all the people who don't enjoy driving or aren't good at it to convert to AI-controlled vehicles, I think the rest of us would be happy to encourage them to do so while we go on our merry way.

I have long advocated that driver's licenses be much more difficult to obtain, and the driving test should be much more difficult to pass. Driving simulators with advanced neural scanning technology should be used to assess reaction times and 3D spatial cognition. Draconian penalties for driving without a license should be implemented. This would get all the worst drivers off the road.

The proficiency level necessary to drive is easy to set. The test should be so difficult that I barely pass it. In fact, I personally should get the lowest passing score possible on the test. Everyone who is a worse driver than me, should fail the test and be banned from the road.
posted by charlie don't surf at 8:09 PM on November 16, 2013 [8 favorites]


The great thing about self-driving cars will be that prople who love to drive will buy a motorcycle and being a rider won't be nearly so dangerous. Win-win!
posted by five fresh fish at 8:15 PM on November 16, 2013 [2 favorites]


My peeve so prevalent in my city is the omnipresent driver who lives in mortal terror of intersections. Here they have a tendency to dawdle and pussyfoot slowly through the light as if an armed Deathcoupe is going to materialize out the ether. This is not safe. An intersection is a dangerous place, a place you hurry through to get to the relative safety of the other side, not feel your way through in slow stops and starts maximizing the time you and those behind you spend in The Dangerzone. Go, go, punch it and live!

To quote the poet Dylan Thomas on the matter: Rage, rage against your irrational fright; but do not brake gently into that green light.
posted by sourwookie at 8:20 PM on November 16, 2013 [2 favorites]


Where there are posted speed limits in Germany, do people also refrain from exceeding that speed limit when passing, or forgo passing altogether if the car in front of them is already doing the speed limit?

I think the speed cameras are doing a good job of enforcement. I have multiple letters from rental agencies letting me know as much.

One thing they don't do, however, is shoot over to the far right lanes to pass someone clogging the passing lane.
posted by JoeZydeco at 8:28 PM on November 16, 2013


sourwookie: "An intersection is a dangerous place, a place you hurry through to get to the relative safety of the other side, not feel your way through in slow stops and starts maximizing the time you and those behind you spend in The Dangerzone. Go, go, punch it and live!"

When my mom was teaching me to drive, her advice was basically: "Intersections and passing lanes: know what you're going to do, check that it's safe, then get in there, do it, and get out. No lingering."

(Mom also had a couple of traffic goddesses she'd call upon when needed. Leap is the goddess of passing lanes and intersections. Squat is the goddess of parking spaces. Her invocation is to chant under your breath as you slowly roll along, "Good, great, gracious Squat — please grant me a parking spot!" Once she obliges, it's advisable to recognize it with "— thank you for this parking spot!")
posted by Lexica at 8:47 PM on November 16, 2013 [8 favorites]


I took a traffic engineering course way back when, when I was in the civil engineering line. The instructor said something like "If you take the 5% worst drivers off the road, traffic speed increases by 20% overall".

Having witnessed innumerable times where one clueless asshole or old person is like some immovable object in traffic, I agree with that assertion.

That was almost 15 years ago. Now every asshole with a hand has a cell phone in it and it's straight up bedlam everywhere.
posted by sanka at 9:09 PM on November 16, 2013 [3 favorites]


I love this stuff.
Check out trafficwaves.org and its FAQ.
The solution appears to be to always open up generous space in front of you and let as much traffic in as wants in.
posted by spbmp at 9:44 PM on November 16, 2013 [2 favorites]


Much of my driving is on Los Angeles freeways late at night or early in the morning. The freeways are large enough and my hours are far enough from peak traffic time that traffic should flow freely. The bozos who create traffic knots stand out like traffic flares. The people going 63, 65, 67, 70, and then 60 mph in the left lane. The people who pull up parallel to the person to their right and then match their speed. The people who push into a faster lane and then camp there at the same speed as the lane they left. If you're paying attention, you can see these people minutes ahead but you can't do anything about them except wait until you can get past them. I don't remember this stuff happening 20 years ago so I believe that it's a result of L.A. drivers getting progressively worse over the years.
posted by rdr at 9:56 PM on November 16, 2013


I am convinced that many highways would run faster with half the speed limit, rigorously enforced. A steady 30 mph is a lot better than mostly 2 mph alternating with 0 mph punctuated with brief stretches of 60 mph.
posted by Camofrog at 11:12 PM on November 16, 2013


I remember watching this occur one evening sitting at the Horizons bar at the top of the Shangri-la hotel in Sydney. Free flowing traffic coming off the Sydney harbour bridge and one car braked to try and merge into the far left lane causing the driver in that lane to also brake. 40 mins and three beers later and the two lanes of traffic were both still bumper to bumper moving at a snails pace until they reached the very spot that the two earlier cars had braked then everyone sped up as both lanes suddenly became clear ahead. Literally thousands of people held up simply because of one action by an idiot an hour earlier, fascinating to watch.<
posted by rafterman at 12:40 AM on November 17, 2013 [2 favorites]


Camofrog - the UK has been installing managed/controlled motorways the past few years in an effort to enforce variable speed limits on busier sections of the major highways and as an alternative to widening. In the past congestion or an accident would cause traffic signs miles upstream to tell drivers to slow down, but of course 99% of drivers would ignore the signs; the result being the backwards moving traffic jam for no apparent reason. On controlled motorways the signs are linked to speed cameras so drivers stick to the variable limits.

IIRC there has also been a recent change in the law to allow police officers to fine drivers hogging the middle or outside lane of a motorway when the inside lanes are clear. I can't see how this can be effectively enforced, but it is probably a step in the right direction in terms of driver education.
posted by lawrencium at 3:03 AM on November 17, 2013


Other people braking could be a sign of some road hazard that they see and you do not.

No, it's not. I can see the cars ahead of Mr. Brakelight, and they aren't behaving as though there were any such thing. Unless the hazard miraculously appears after the car he's following, then disappears before I get there, there isn't any hazard other than Mr. Brakelight's random foot-twitch. I can also see all the cars in the adjacent lanes, and none of them are doing anything to indicate that they're going to impinge on our lane, nor do they do so.

And before somebody goes there, no, I am not following so closely that Mr. B is tapping his brakes to tell me to back off.

It's disruptive, because of all the people who see brakelights and reflexively step on their own brakes without assessing whether they have to. One chain of mindless action causes everyone behind to have to slow down.
posted by Kirth Gerson at 4:13 AM on November 17, 2013 [1 favorite]


Be the traffic you want to be stuck in.
posted by srboisvert at 5:19 AM on November 17, 2013 [2 favorites]


I don't remember this stuff happening 20 years ago so I believe that it's a result of L.A. drivers getting progressively worse over the years.

Or the freeways getting more congested, perhaps? I wouldn't be surprised if traffic numbers are up by 50% or more over that time. There is a point in increasing congestion where this stuff matters; with less traffic people can just move through.
posted by Dip Flash at 5:42 AM on November 17, 2013


Don't worry, Google will solve this problem with their driverless cars. Google will solve all our problems. All hail Google.
posted by spitbull at 6:44 AM on November 17, 2013


Another reason for excessive braking is a driver following to close to the driver in front of them. This is also one of the major causes of traffic accidents! You should leave at least a car length between you and the driver in front. Even more space when following transport trucks (you should be able to see their mirrors).

I don't think it's generally the slow drivers causing the traffic jam - it's the excessive speed drivers. They speed up until they catch up to the next driver and then brake. And then everyone else brakes. If everyone followed the speed limit - and gave proper space between vehicles, traffic would likely flow much easier.
posted by what's her name at 7:39 AM on November 17, 2013 [2 favorites]


You should leave at least a car length between you and the driver in front.

Yes. At a red light. On a highway, you need way, way more than that.

(Two chevrons!)
posted by Sys Rq at 7:43 AM on November 17, 2013 [4 favorites]


In my experience , people who "enjoy driving" and who think they are "good drivers" are somewhat more likely than the average driver to be the ones who need to be replaced by robots.
posted by yoink at 8:00 AM on November 17, 2013 [2 favorites]


Kirth Gerson: "
No, it's not. I can see the cars ahead of Mr. Brakelight, and they aren't behaving as though there were any such thing. Unless the hazard miraculously appears after the car he's following, then disappears before I get there, there isn't any hazard other than Mr. Brakelight's random foot-twitch. I can also see all the cars in the adjacent lanes, and none of them are doing anything to indicate that they're going to impinge on our lane, nor do they do so.
"

You haven't driven much, have you?

I've had it happen enough that yes, I'm your nemesis, Mr Random Foot-Twitch.

80,000lbs of truck doesn't stop on a dime, yet many seem to think it does, and they *do* pull out of their stopped lane into mine (and yours, if you happen to be behind me). I *prefer* not to hit them, despite the education that experience might provide them.
posted by Sportbilly at 8:35 AM on November 17, 2013


I knew it!

It is one idiot slowing everybody down.
posted by Sphinx at 9:07 AM on November 17, 2013


You haven't driven much, have you?

Only 50 years' worth. You clearly do not understand what I'm talking about. These people are not reacting to actual or threatened events. No one cuts into their lane, or attempts to, or even looks like they're going to, even after Mr. Brakelight slows down. No one else in their lane is braking. The only thing they are reacting to is brake lights in other lanes. The times I see this happening, there are no 80,000-pound trucks in evidence, just normal vehicles, so you can put that strawtruck away for another discussion.
posted by Kirth Gerson at 9:08 AM on November 17, 2013


It's not a strawtruck, it's the one I drive every day.

Maybe you don't see people cutting lanes as you say, but I would argue your experience isn't particularly representative, given how often I do see it.

I'll continue screwing up your traffic a little in my continuing efforts to not screw it up a lot with a wreck in the lanes that *were* still moving. :)
posted by Sportbilly at 9:31 AM on November 17, 2013


I will also say that I also see the lane-cutting out of the stationary lane when driving a car, I failed to mention that earlier, I apologize if that caused any confusion.
posted by Sportbilly at 9:39 AM on November 17, 2013


People should follow spbmd's link above. The root problem is people following way too closely such that the lack of slack forces large speed changes which create those persistent waves.

That writer sort of makes one mistake, though. He says that perfect robot drivers will have the same problem, but he's not accounting for differences in reaction time (though car performance is the real limiting factor here) and availabity of information. He points out that if everyone knew to simultaneously accelerate when an obstruction clears, the wave would immediately evaporate. But networked robot drivers could do that. More to the point, though, is that's the limit toward which decreasing reaction times approach. In turn, reaction time is what makes car spacing slack so important. So much faster than human reaction times would allow closer spacing (more cars on the road) while avoiding the strong, persistent waves.

With regard to the braking thing, I think we each may be envisioning different scenarios. I took it to be about heavy enough traffic where I can't be sure that a car in an adjacent lane isn't braking for a reason and that they're not likely to be motivated to suddenly move into my lane. Bottom line, though, is that I'm not going to desist in defensive driving so as to exchange safety for higher speed. I assume other drivers have poor situational awareness and make poor, impulsive and sudden decisions and that what can go wrong likely will.
posted by Ivan Fyodorovich at 9:40 AM on November 17, 2013 [1 favorite]


Rural interstate traffic tends to flow in packs of varying speeds. One pack approaches a slower pack, then works its way through it. If drivers leave a passing lane open this transition happens fairly smoothly. If a dawdler blocks the passing lanes the packs merge, and for a while many of the cars will be traveling too close to the car in front of them. Sometimes one of the gofasters will try to jump the line by getting into the slow lane and passing others in the queue. This is what I call a "stupid contest." One guy in the passing lane gets pissed at the gofaster, and creeps forward so the gofaster can't get back into the passing lane. Sometimes the gofaster tries to make it fit anyway, and two cars are bumper to bumper at 70 mph. Most times they are lucky, and get a chance to spread out a bit, but now and then they tangle assholes and somebody gets hurt. As far as the other drivers on the road are concerned, a stupid contest is usually a tie.

Traffic waves are inevitable in heavy traffic, but the anus-clenching aspect of them can be reduced by keeping a greater distance between you and the car in front of you. Here's my version of this: When the speed fluctuates, even assuming everyone responds correctly with just a tap on the brakes, your reaction time is added to the reaction time of all the guys in front of you. Let's say that the average reaction time is 1/10th of a second. By the time the brake lights on the car in front of the 11th guy come on, the line will be a whole second into the slowdown. At 60 mph, a second translates to 88 feet. In real life, this means that the 11th car will have to brake significantly harder than the first car did in order to match his speed to the new speed at which his line is now moving. Sometimes the friction coefficient won't cooperate.

The way to minimize this effect, of course, is to try to read the brake lights as far ahead as you can see, not just the guy in front of you. Truck drivers can do this more easily that the average motorist, because their eyeballs are about ten feet off the ground. The savvy driver will leave as much space as is practicable between him and the car in front, so that the he can brake more easily and reduce the inevitable effect of lag time, which will help the guys behind him to avoid making hasty decisions at a high speed.

I realize that Everybody Is a Good Driver, even those assholes who used to like to draft my big truck to improve their gas mileage. When I drove over the road, I figured that the difference between 55 mph and 65 mph was about 100 miles on a 10-hour day. It's easy to calculate how much time you'll save on trips across town (a few seconds, a few minutes), and--at freeway speeds--a hour's driving will save only ten minutes, so maybe it's best to just putt along with us slow guys, and let the gofasters have all the fun.

My tactic was to find a pack in the traffic that traveled at about the speed I wanted to do, and then set up twenty or thirty meters behind a steady driver...further at night, because, even on low beams, it's annoying to have some asshole's lights in your mirrors, and I'll avoid doing that when I can. When I notice a pack of gofasters approaching, I just hold what I've got while the pass us. This keeps my blood pressure down, and I actually get to see one the gofasters, now and then, off on the side of the road negotiating his most recent speeding permit with a local State Trooper.

I well remember those phantom kinks in traffic. CB info would tell of an accident that happened downstream of that place a few hours before, and the ripple was still alive. It doesn't take a wreck to make those ripples, just a few clueless drivers having a stupid contest.

(Northbound, you have a brake check at mile marker 217, right lane's stopped, left lane is creeping, smokey's got flares on the ground....)
posted by mule98J at 11:29 AM on November 17, 2013 [3 favorites]


Maybe you don't see people cutting lanes as you say, but I would argue your experience isn't particularly representative, given how often I do see it.

Of course I see it, but that is not happening in the situations I am talking about. If you don't see people braking for no reason, maybe it's your experience that's unrepresentative.
posted by Kirth Gerson at 1:02 PM on November 17, 2013


Kirth, Are you referring to people braking in the other lane for no reason at all, or are you referring to the people in your lane braking because the other lane is slowing because of congestion?
posted by Sportbilly at 1:31 PM on November 17, 2013


At the current volume of drivers I think the only actually workable solution is computerized driving systems that are networked together.
posted by odinsdream at 2:36 PM on November 17, 2013


I'm surprised no one noticed this earlier.

When I was in college I took lots of classes in acoustics. And one of the things you end up doing is playing around with wave propagation through Slinkys (like this).

And post-college, the first thing I noticed when I was up in a tall building looking down at traffic on a freeway (in Seattle, where people drive like geriatric lude addicts) was that the slow-downs propagated backwards like a wave in a Slinky (or like ripples on a pond, if that works better for you).
posted by Relay at 5:48 PM on November 17, 2013


Sportbilly, I'm talking about people in my lane braking only because people in other lanes are doing it. I see it happening in other lanes, too, but that doesn't affect me as directly, so it doesn't bother me.
posted by Kirth Gerson at 6:41 PM on November 17, 2013


Relay, I've called it the Slinky Effect for years, because that's pretty much how traffic behaves.
posted by Kirth Gerson at 6:42 PM on November 17, 2013


That's what I thought you were talking about, I too brake in those situations, and it's prevented many pancaked cars. But YMMV, obvs.

You're right about the slinky, better to have extra space to reduce braking into a jam, but when the lane next to mine is jamming up, I'll go with caution over speed any day, regardless of my cushion.
posted by Sportbilly at 7:12 PM on November 17, 2013


If I had good visibility and knew that someone in an adjacent lane seemed to be braking only to reduce speed and for no other apparent reason, I probably wouldn't brake in response.

But I might. Because I can't really know why that person is braking. If I can't see any good reason for it, then that would possibly make me more cautious, not less. I don't know exactly what that guy is going to do. I'm not going to be eager to inevitably move immediately into his blind spot because I've not slowed down when he's braked for a reason I can't identify.

If he does have a reason, like the person in front of him is braking, then I will also be cautious because I don't know that he won't decide, just after he brakes, that my lane wouldn't be faster and that this will happen right as I move into his blind spot.

The funny thing is that Sportbilly and I assume that either that person has a good reason to brake (and therefore it may well affect me) or that they are, in a word, an idiot or something. The last part also makes us be cautious. In contrast, Kirth sees someone he thinks is an idiot and then assumes that the idiot won't do something idiotic like swerve into his lane and collide with him.
posted by Ivan Fyodorovich at 8:09 PM on November 17, 2013


They might be signalling to following traffic, not really braking. A quick tap isn't really a slowdown, it's chatter: "ooh! I'm not sure what's going on! Be careful!" (STFU, chatterers! Ppl are trying to drive!)
posted by five fresh fish at 12:13 AM on November 18, 2013


I do not assume that people in other lanes are idiots for braking. I am paying less attention to their lane than I am to my own, because it's stuff in my lane that I'm going to hit if I don't pay attention to it. That includes any of them who decide to change lanes, of course, but after driving the same roads at the same time of day for something like 25 years, I don't get surprised often, and haven't ever collided with anybody doing that.

All that said, I know that there are sometimes good reasons that others brake when I wouldn't. Some cars don't slow down much when you lift your foot. I've driven a couple of Ford products that seem to have had all the compression braking engineered out of them; to slow down appreciably, you had to apply the brakes. I am sure there are others.

In the specific situation that prompted all this discussion, the braking car in my lane doesn't need to slow at all - the car ahead of them may actually be drawing away from them. And it's not that they're slowing to make a lane change of their own, because they don't. They just keep on driving in the same lane. The result of their brake-spasm is production of a slinky that wasn't there before and has no reason for being, and that's what bothers me.
posted by Kirth Gerson at 6:43 AM on November 18, 2013


The worst of these jams occurs on highways where there's a curve followed by a downhill, then uphill. Folks come around the curve and see the cars not just immediately in front of them, but waaay up ahead, too, and they touch the brakes instinctively. That, and the apparent inability of most modern cars to maintain speed up even modest hills.
posted by MrMoonPie at 7:31 AM on November 18, 2013


Then there's the situation where traffic's steaming along, and rounds a curve to meet the rising or setting sun head-on. Some drivers may be completely blinded, and who can really blame them for hitting the brakes? Thanks to DST, many people who encounter this on their commute get past the days when it happens, then have another stretch of more of the same.
posted by Kirth Gerson at 7:59 AM on November 18, 2013


mule98J: ...then set up twenty or thirty meters behind a steady driver...further at night, because, even on low beams, it's annoying to have some asshole's lights in your mirrors, and I'll avoid doing that when I can.

You're now my favorite person ever, because you are a rarity: Someone who realizes, in traffic, that other people are people and have sense organs with the same limitations as yours, neurological makeup similar to yours, and reflexes similar to yours.

This links to why it's very hard for me to maintain a safe following distance on some roads---I try to leave three, four car lengths' worth of distance, which the lanediver next to me interprets as "please jump in and cut my following distance in half instantly!"

Speaking to the OP in general, this is amusing and slightly nostalgic to me, because it was one of the projects in a Numerical Computing class that I took a long while ago and really enjoyed. The relevant mathematics is here (and it's been a Known Thing for a long time). But this simulation's interface and setup are very well-done.
posted by seyirci at 12:16 PM on November 18, 2013


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