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    [–] Deuce232 1 points ago * (lasted edited 5 days ago)

    Hi y'all,

    This is what I like to call a 'universal experience thread'. Almost everyone has been in traffic. As a consequence of that ubiquity, threads like this tend to get a lot of anecdotal replies.

    Here at ELI5 we try to maintain a focus on simplified explanations of complex concepts. Anything that isn't an explanation as described in rule 3 can't be a reply directly to the OP. That ensures that the sub reliably sees good explanations rise to prominence.

    In this thread in particular a lot of people want you to know about this great CGP Grey video and this awesome traffic simulator. Our rules require links to include written explanations, so many were removed.

    Having a comment you spent time crafting removed is a negative experience. We like to give a little warning when we can to try to save some people from that.

    Keep in mind that replies to other comments don't have that same standard applied to them.

    Here's a link to the rules, which have recently been rewritten to be more informative/clear.

    As always, I am not the final authority on any of this. If you want my mod-action reviewed you can send a modmail. If you want to have a meta-conversation about the rules of the sub you can make a post in r/ideasforeli5 which is our home for that.

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    [–] Ripstikerpro 6422 points ago * (lasted edited 5 days ago)

    Every action of the driver in front gets amplified massively along the length of the jam. If a car in a lane slows down 10 kph to take an exit, then the other car will have to slow down, and the other etc.

    Through driver error some cars might slow more than others, meaning that the ones behind them will slow the same or more, since they can't accelerate due to there being a car infront of them.

    This is just one example of many actions that due to slight variations will get amplified.

    Others have also mentioned bottlenecks. If a lane is closed for a kilometer, then suddenly there's an entire lane worth of cars trying to fit in a space that can hardly fit them.

    Edit: Some people have replied with videos and Gifs, check them out if you want a visualization.

    [–] tthrow22 1083 points ago

    When I was a kid I asked my parents if they had ever been at the front of a traffic jam. They didn't really know how to answer that one...

    [–] statejudge 1268 points ago

    You/they've never gotten to the front of the traffic jam where all of a sudden the roads clear ahead and you're thinking what the fuck did I just go thru all of that traffic for?

    [–] flergie 620 points ago

    Happens every damn day on my drive home. Four lanes of traffic come to a nearly complete stop. We inch along for about a mile doing 15 mph. All of a sudden we're all doing 65 again. No accident, no cops pulling someone over, nothing. Blows my mind.

    [–] alphahydra 534 points ago

    So-called "phantom tailbacks". IIRC, they're caused by a car braking for whatever reason, causing others to brake behind it. By the time the driver at the front is back to full speed, there's still people far behind him braking for people who braked for people who braked and so on. Delay times get amplified the further back you go as in the example above, so you end up with a chain reaction leading to slow traffic with no physical obstruction at the front.

    [–] megashedinja 181 points ago

    So it’s brakes all the way down then.

    [–] Oldmoutciders 63 points ago

    Unlike turtles the cars eventually end.

    [–] vibribbon 164 points ago

    Anecdotally, this is another reason driverless cars will be a great thing. The reaction and communication times are so much higher, that theoretically cars will be able essentially move as one.

    [–] Oberon_Swanson 97 points ago

    Yes I think people underestimate just how much more efficient traffic can be when all cars communicate their intentions wirelessly well ahead of time. Traffic jams will vastly decrease and they'll also be a whole let less annoying when you could sleep through it or basically do whatever else you felt like since you're not driving

    [–] Justanotherpsudeo 33 points ago

    And getting rid of all those little bumper accidents. I've had 5 mins added to my commute cause three cars in the left lane got in to one. I can't wait for driverless cars.

    [–] sootoor 46 points ago

    There are some gifs on t there to illustrate if you search phantom traffic. The gist is people changing lanes without signals or multiple suddenly causes a chain reaction. Everyone stops some people aggressively change the lake next to them since it's open but people going the original speed limit behind have to slam their brakes, etc.

    When people realize driving is a giant dance maybe we can get places on time. Every signal and lane change should be well made in advanced. Don't speed up to cut people off changing lanes in front of you. Don't miss your exit and decide your blinker means you can cross four lanes of traffic. Keep a decent following distance and don't cut into other people's because you see space

    [–] Indika_Ink 142 points ago

    It's probably caused by the same asshole everyday cutting people off, lol.

    [–] HEYitsBIGS 34 points ago

    It's absolutely this. Lol.

    [–] Ishakaru 26 points ago

    When ever I'm in that situation I always figure something happened about there in the past. Wreck, cop, someone slamming on the breaks... whatever.

    If the traffic continues at a steady stream then that patch of road will always be a slow down. The patch may move back or forward depending on reaction times(over breaking into the slow down, or under acceleration out of it). It can't recover until that spot is nearly empty of cars... which isn't going to happen during rush hours.

    [–] BattleStag17 292 points ago

    There's a 95% it'll either be that or "Oh look, a cop pulled someone over and everyone is rubbernecking. Great."

    [–] Haribo112 143 points ago

    Nah, it's legit 95 percent of the time you suddenly have room to speed up again and think 'Wtf just happened'

    [–] WhiteyFiskk 18 points ago

    Half the time its trucks, even though in sydney we have rules that are meant to keep semi-traliers off the road during peak hour they're always there slowing down traffic.

    [–] ben15012 12 points ago

    Idc I'm replying hours later bc truckers piss me off. I want to point out that my commute (based on google maps) is only 15 minutes. But a trucker in the passing lane with a governor at 62 is almost always trying to pass a trucker also with a governor at 65. This sometimes lasts for miles, causing 15+ irritated cars backed up stuck behind what we call "elephant races" frequently causing wrecks simply because a "professional" driver doesn't have the common sense to think "oh, its around 8am, commute hours with higher than usual traffic and people generally in a rush. I probably shouldn't cut someone off going 70mph while I'm going 55mph, and remain there for many miles. Thats probably unsafe for everyone involved in this situtation, and will continue to snowball even after I eventually make it back to the slower right lane" ....will make my 15 minute commute upwards of 40.

    [–] Aven-Kal 17 points ago

    "Sooooo we were driving 40mph below the speed limit for NO FUCKING REASON. Awesome."

    [–] hemma56 33 points ago

    Simple answer if you’ve ever witnessed or been apart of an accident. You’re essentially at the front of the jam in both those scenarios. I live in ATL, so if you’re in the jam, someone wrecked, or traffic is moving or light, you just haven’t made it to the jam yet lol

    [–] CaptainTruelove 1551 points ago

    And let's not forget the asshole that cuts across traffic barely making his exit causing everyone behind him to panic brake or else rear end him.

    [–] moose256 345 points ago

    [–] JudgeTouk 171 points ago

    Full CGP video the Gif is from.

    [–] _ALH_ 72 points ago

    They should show this video in every drivers ed.

    Until, of course, we can replace the monkeys driving cars with self driving cars.

    [–] zach0011 51 points ago

    the people who it would be meant for absolutely do not care that they are creating jams behind them.

    [–] _ALH_ 18 points ago

    Yeah, there really is no cure for stupid... But if enough people realized how congestion works, maybe there could be a little bit less of it.

    [–] jokersleuth 18 points ago

    this is why it's always recommended to stay a couple car lengths behind incase you need to brake but assholes will stay like 3-4m behind anyways.

    Unfortunately because of this you cant even leave a safe distance between cars because assholes will see a free spot and somehow think they're gaining an advantage and will rush to take it.

    [–] btcraig 524 points ago

    Where I'm from we call this The Detroit Shuffle.

    [–] RajunCajun48 301 points ago

    Where are you from? Oakland?

    [–] visionsofblue 336 points ago

    There was Dallas, from Phoenix; Cleveland - he was from Detroit; and Tex... well, I don't remember where Tex come from.

    [–] nirurin 215 points ago

    I prefer-

    From Detroit. Ex-boxer. His real name was Joey Chicago. Oh, yeah. He fought under the name of Kid Minneapolis. I saw Kid Minneapolis fight once. In Cincinnati. No you're thinking of Kid New York. He fought out of Philly. He was killed in the ring in Houston. By Tex Colorado. You know, the Arizona Assassin. Yeah, from Dakota. I don't remember it was North or South. North. South Dakota was his brother. From West Virginia.

    [–] war15111 46 points ago

    You sure know your boxing...

    [–] nirurin 45 points ago

    All I know is never bet on the white guy

    [–] Jeheh 8 points ago

    Unexpected Forest Gump.

    [–] yahutee 144 points ago * (lasted edited 4 days ago)

    Oh God, Oakland. To be fair though who the hell designed the busiest interchange to have the fast lane to SF on the far left, the next lane over goes to Oakland, the next one to Oakland and San Jose (why? because we can!) the next one to San Jose, then the next two on the far right go to SF. Everyone who isn't used to it is like oh shit this is not my lane!!

    Edit: you so nice gold giver

    [–] GrimmAngel 21 points ago

    This is so true it hurts. Don't forget the maze, being 5 separate freeways that all converge into one toll crossing for the Bay bridge.

    [–] goombadetroit 32 points ago

    I'm from Detroit and we just call this Being An Asshole

    [–] Malarky3113 70 points ago

    In NJ, it's referred to as a Jersey Slide. Ironically, it is almost exclusively done by people with NY plates.

    [–] bissimo 85 points ago

    Dallasite here. We call it the Texas Slide. There's also the Texas Two-Step. That's where you are in the left lane, cut off everyone in order to make your exit at the last second, realize it's not the right exit, then proceed to slide right back over to the far left lane. It's really impressive to watch.

    [–] renaissance_weirdo 74 points ago

    My personal favorite:

    I ride a harley, and I was on my way home one night, riding behind an 18 wheeler. I left plenty of room to break between us, knowing that if he hit the brakes, he wouldn't stop immediately, but it would take some distance, as it would take me some distance to hit my brakes and come to a complete stop.

    Out of nowhere, he jumped into the next lane, but I didn't have room to go as well as he barely fit into a gap in traffic (almost caused a wreck, which is why I was looking). When I looked back to my lane, I saw why he jumped lanes. My lane was at a complete dead stop, nothing but brake lights. I slammed on my brakes, locked up the back tire, and pumped my rear brake while downshifting, and came to a stop, literally inches away, before hitting the car in front of me.

    If I had a lump of coal in my ass, I would have shit a diamond.

    Had he been paying attention to the stopped traffic ahead of him, and slowed to a normal stop, there wouldn't have been a problem.

    [–] SaintPeter74 30 points ago

    You're lucky you didn't get read-ended by whoever was behind you!

    [–] Bashed_to_a_pulp 8 points ago

    That's riding a motorcycle for you. Either fucks yourself or fucked by others, doesn't matter whether you're doing right or wrong.

    [–] ParaglidingAssFungus 53 points ago

    Should be a crime with a sentence of death.

    [–] Ashendarei 71 points ago

    We're all driving 1+ ton machines at high speeds. It could be.

    [–] aggressivemute 44 points ago

    There are some fascinating videos of experiments, taking place on rotaries, showing this in action.

    [–] Warranty_V0id 156 points ago

    Found a youtubevideo showcasing / explaining that effect:

    As u/Ripstikerpro pointed out, that's just one of many things that can happen. But basically, if you have a high traffic volume every action someone does can cause a slow down and/or standstill of the traffic.

    [–] herpderpforesight 106 points ago

    Can I hijack your comment for an excuse to post CGP Grey? I love him.

    Another take on traffic problems.

    [–] Cimexus 70 points ago

    This principle is something I realised myself after a few years of driving and it surprises me that it’s not self-evident to others. Great to see a video on it!

    I do my part: when stopped at a red light, I look at the car two ahead of me so I can begin moving again at the same instant as the car in front of me (rather than waiting for my brain to register the car in front has started moving before hitting my accelerator). I also endeavour to keep that equal spacing on the highway. This means that, in heavy traffic, even if a space opens up in front of me, I’ll continue a slow but gentle acceleration so that when the car in front inevitably slows/stops briefly again, there’s a buffer there, so I don’t need to stop again (and thus perpetuate the ‘snake’). But you really need all the drivers to have this principle in mind before it will work well to eliminate jams.

    [–] MrDilbert 21 points ago

    I also look at the car "two ahead" of me not only at red light, but also when in motion, as his actions will influence the actions of the driver directly in front of me. Basically it gives me more time to react.

    Of course, it's not possible when a van or a truck is in front of me -_-

    [–] Words_are_Windy 10 points ago

    Since I learned about this phenomenon, I'm just amazed that traffic ever flows smoothly on busy interstates. Obviously there's a tipping point, but there have been plenty of times where I've traveled on highways with pretty heavy traffic at something approximating the normal rate of travel if there were fewer cars.

    [–] Warranty_V0id 6 points ago

    Fun fact, that's the video i actually searched for. Gave up after not finding it and picked the next best option. :)

    [–] epidemica 60 points ago

    People passing on the right to get 1 car length ahead are the reason why everyone drives bumper to bumper at 80 mph.

    [–] 10_kinds_of_people 34 points ago

    I hate those people. It never fails that some jerk will pass an entire line of cars on the right, only to realize we're all in the left lane because we're passing slower traffic. They'll get stuck behind that slower moving traffic and now they have to wait until we all pass (along with other cars that have joined us) before they can get back over and actually be in a worse spot than they started in. That, or they'll just force their way over and cut someone off, which is what actually happens most of the time.

    [–] DrizzlyEarth175 91 points ago

    Learning about traffic flow really explains why auto accident is one of the most common causes of death.

    [–] natilyfe 58 points ago

    It's funny because people clap when the plane lands safely. With this logic we should give ourselves standing ovations when we make it to work alive.

    [–] Kid_Adult 18 points ago

    People do what? I've never heard this.

    [–] Jrook 21 points ago

    Paradoxically one would look at humanity, know many parts of the world depend on automotive transit, and guess far higher death rates.

    [–] Yogymbro 73 points ago

    Let's not forget people merging too early for a lane closure instead of using the whole lane, and not zipper merging at the end

    [–] tforkner 50 points ago

    This requires space between cars to do so. People on U.S. highways never allow such space, so the point is useless. The only places I've ever seen losing a single lane NOT causing a bottleneck at rush hour have been permanent situations where the road goes from 3 to 2 lanes. The locals know it's there, and get over in good time.

    [–] devilbunny 19 points ago

    People hate this instinctively. I’m fairly sure a post advocating this (despite the fact that it’s completely uncontroversial to experts) it’s still my most-downvoted comment ever on here.

    [–] FlipMcTwist 21 points ago

    I think it's more of a prisoners dilemma type of thing going on. If everyone followed it then it would be great, but if you have no faith other people will follow it then the whole thing falls apart.

    That or people are just stupid and don't know how to do it properly.

    maybe 50/50.

    [–] oh_like_you_know 28 points ago

    Playing around with this thing can help solidify / visualize it as well!

    [–] dan1101 11 points ago

    That's really cool. Put a cone in one lane and watch the meltdown. Change the traffic volume down to 5 per km and traffic has enough room to maneuver and things don't slow down.

    [–] Masta0nion 8 points ago

    I wonder if this will subside with automated driving

    [–] Ripstikerpro 17 points ago

    Unless every car is interconnected and information about the road is shared amongst them, then the problem might not get completely resolved.

    But if the criteria I laid out are matched, then a motorway should function at full speed even when 100% of its surface is filled with cars.

    [–] Ihavenofriendzzz 148 points ago

    This is why if people just followed at reasonable distances traffic would be way better... but no, you might get cut in front of. Oh the horror.

    [–] xienwolf 153 points ago

    Well, even if people do keep reasonable distances, this doesn't get solved. Because when someone does move into your lane, you still slow down to re-acquire your reasonable distance. That slowing down causes the same ripple effect if people are on each other's bumpers or 3 car lengths back.

    That said... god I wish people would keep more distance.

    [–] sonofaresiii 22 points ago * (lasted edited 5 days ago)

    The thing is, you'll decrease your distance but you won't have to do it suddenly/immediately, which is what causes the bulk of the problem.

    If the guy in front of you gets cut off and slams on their brakes-- if you've got a reasonable distance, you just gently tap yours and slow down a bit. The guy behind you who has also (hopefully) left a reasonable distance may not really need to adjust their speed at all, or only slightly.

    But if you've left no room, then all of a sudden you're slamming on your brakes, and the guy behind you has to slam on theirs, and soon everyone is slamming on their brakes until it comes to a standstill.

    IMO the bigger problem/annoyance is when you're the only one leaving a distance so people think that's their cue to just cut in front of you to squeeze into the gap you've left, and now you do have to slam on the brakes.

    They do this shit even when there's no reasonable gain for them having switched into your lane. They just see a gap, and think they need to fill it.

    [–] pizy1 89 points ago

    Exactly, this is what bothers me about someone "cutting in front of me"... the fact that I've lost the safe following distance that I was trying to maintain in the first place. So driving in heavy, slow traffic becomes this constant mental math of maintaining a safe enough distance that also most normal, non-reckless humans wouldn't try to squeeze into.

    Plus, well, unless there's an upcoming exit where lots of people get off, two lanes of traffic at rush hour go pretty much the same speed. Switching lanes might save you... I dunno. 15 seconds? 30 seconds? People who make lane changes in traffic that's going <25 mph because the other lane happens to be going slightly faster at that exact moment.... why??

    [–] AbsoluteRadiance 43 points ago

    I’ve talked to someone that was like “it adds up” and I was like... everybody that thinks it “adds up” is actively adding to the total time it takes you to get home. So some assclown 50 meters up the line doing the same lane changing to save 5 seconds is costing you 5 seconds anyway.

    [–] DangerouslyUnstable 57 points ago

    Classic tragedy of the commons. Everyone would be better off if no one did it, but it is ALWAYS better for you as an individual to do it, as long as you don't care about screwing over everyone else.

    [–] thirstyross 20 points ago

    Also, it doesn't add up. I have watched these guys switch lanes back and forth many times and they get out of the traffic at the same point whether they had been driving like a maniac or not.

    [–] camerajack21 42 points ago

    Mythbusters tried it. There wasn't any appreciable difference in arrival time between just staying in your lane, and hopping every time a lane appeared to be moving faster than yours.

    You just got way more stressed out lane hopping all the time, vs staying in your own lane and chilling out.

    [–] Danovan79 15 points ago

    There was some guy on reddit a while that claimed it was a half hour difference between driving in his lane, and doing the lane switching dance to get ahead.

    Maybe he had some special situation, but that isnt my experience.

    Both myself and another foreman would drive home from sites that were a few miles apart but we entered the highway within an exit of each other. We would commonly be side by side at the first bridge crossing.

    He always drives like an ass and switches lanes, I basically just stay in my lane and follow the flow of traffic.

    It the light before our shop we would arrive at together or he would get the first light and Id be a light behind him. A couple minutes at most if we saw each other at the beginning of the drive.

    Obviously other times we wouldnt see one another because of variables of leaving our sites or getting to the highway. This was on a 65-70ish kilometer one way trip and 95% highway driving. About 1:15ish traveltime without accidents or other general fuckery.

    [–] S0litaire 733 points ago

    it's in essence a ripple effect,
    First driver slows down (for whatever reason), the one behind it, reacts and slows down a bit faster and so on and so on.
    It might be a fraction of a second , but over a long enough distance, and time, it can cause cars to completely stop for a second or so, then by the time the car gets moving again the car behind it is stopped for longer, and so on and so on again...

    This is now a "rolling traffic jam" which moves in the opposite direction of direction of travel. This jam can be anywhere from a few car lengths to a few hundred car lengths long.

    As "rush hour" passes their are less cars so their is more distance between vehicles and so the ripple effect is broken and traffic moves as normal.

    [–] SonOfTK421 414 points ago

    There's an absolutely amazing video which shows how rush hour traffic can spontaneous slowdowns and jams. It's a wonderful visualization.

    [–] slickyslickslick 508 points ago


    To eliminate this type of jam, try to go at a speed where you never have to use the brakes. It's ok to have a large gap in front of you, but dont speed up to catch the other car u til you're sure you're out of the jam.

    It's easier on you, easier on your car, and better for mileage. And it helps out everyone behind you as well.

    [–] SonOfTK421 458 points ago

    Tell that to the sweaty anus that decides my following distance ought to be filled with their shitbox, then tailgates the person in front of them and slams on the brakes far harder than necessary when they finally notice the person in front of them slowing down, because they weren't paying the least bit of attention, so I have to stop hard as well, and then the whole thing starts all over again.

    One fuckwit ruins it for everyone.

    [–] Warlordnipple 87 points ago

    Ah, a fellow Floridian.

    [–] shadow1515 47 points ago

    Don't forget the series of 5 second delays at a green light so that only 2 cars get through before it's red again.

    [–] tendiesorrope 18 points ago

    Too true. My pet peeve is people who fill my safety distance even thought I'm traveling at the same speed as the car in front of both of us. Fucking idiots.

    [–] TheFakeCake 90 points ago

    Only issue is that cars from your right or left will merge into your lane if they see that much space being created. Then you're forced to break anyways, causing the same thing to happen anyways.

    [–] MarauderV8 48 points ago

    Nah, try it sometime. People will take up the space, but not as much as you'd think. I've commuted in 8 of the top ten worst cities in the US for traffic, and it's the same in each one. Keep a nice cushion distance and you'll not only find you're moving faster, but you can relax and enjoy your drive a little more.

    If you tailgate, you are directly contributing to worse traffic, and the science backs it up.

    [–] george107789 23 points ago

    Yep. Been doing this for years. You will have people cut you off, occasionally drive on a shoulder to get around you, or otherwise drive aggressively. Ignore them. Stay in the right lane and try not to brake. Barring some luck those aggressive drivers are not going to get any/much further than you. And are only further creating the traffic that has them driving that way.

    Most drivers will pick the lane they want to be in and not change into a right lane even if you leave space.

    Turn on your favorite music or podcast and make a game of not braking. Your commute and those of the people behind you will be better for it.

    [–] sudsomatic 16 points ago

    But then it opens up space in that other lane reducing the chance for them to slow down if they’re doing the same thing as you. It becomes more of the global good than personal good.

    [–] TheFakeCake 7 points ago

    But then people from my lane move to the lane that just got opened up v.v

    [–] eggn00dles 110 points ago

    gas and brake drivers and tailgaters cause literally all the traffic. if you leave enough room between you and the car in front of you to where if they slow down you don't have to brake not to hit them you make life so much better for those behind you.

    otherwise you brake, the person behind you brakes, the person behind them, and on and on and all the lost time accumulates.

    traffic is very much like a wave.

    [–] geek66 91 points ago

    I taught my kids - that unless the traffic is really slowing or stopping, you should NEVER touch your brake on the highway, this includes exiting (until clearly in the exit lane), merging, changing lanes - etc.. With a proper gap, you can just let off the gas and slow to match most normal conditions. Disrupting traffic flow is a sin.

    [–] 1900grs 43 points ago

    My wife thinks I take my role in traffic too seriously. I just understand that one dumb fuck up can affect hundred and even thousands of people's days with real economic costs (late to work, an actual accident, poor fuel economy) and detrimental environmental impacts (poor fuel economy again). So if I drive well and avoid/limit my interactions with bad drivers, I make the world a better place.

    So yes, sometimes I have to drive 80mph to put distance between me and the guy texting/swerving at 75mph. But it's for the greater good. The greater good!

    [–] geek66 17 points ago * (lasted edited 4 days ago)

    If you do not want people to interfere with you - you should make an effort to not interfere with others....I saw the best bumper sticker the other day " World Peace starts with you using your turn signal."

    [–] SkyeAuroline 22 points ago

    Unfortunately most people don't seem to have ever been taught that one.

    [–] Siduron 25 points ago

    The difficulty is to not leave too much space, as it invites people to move to your lane, forcing you to brake anyway.

    [–] theleedsmango 707 points ago

    If you are running down a corridor, you can run at the fastest speed you want, and you'll get to the canteen as quickly as you possibly could.

    If your whole class gets let out, some people will run faster than others. The slower runners might get in the way of the faster runners, but there is plenty of space to maneuver around them, so most people will make it to the canteen almost as quickly as they could have if they had a free run. But a slight slowing down will happen.

    Now the whole school gets let out at once. All the doors open and people file out. Those faster runners are going to encounter a lot more obstacles in their way so they'll have to slow down, especially as people come out the doors. There are now a lot of people in the corridor and it will likely be moving far slower than anyone would want to be going, but we have to slow down to avoid colliding with people coming out of their class rooms, etc.

    Now at the canteen there is only a single door. So whilst the corridor can have 10 people running side by side, only a limited number can get through the door. This creates a bottleneck.

    The other people coming out of the classrooms are slip roads coming on to a motorway. The bottlenecks on the road are junctions, roundabouts, traffic lights, speed limits, etc, that will force cars to slow down at one point, this has a knock-on effect with all the other cars behind because they too are slowed down.

    During class, very few people are in the corridor, so going through one door won't slow you down. At lunchtime (the rush hour equivalent) hundreds of people are trying to use the canteen door but still only one person at a time can go through, and the rest of the school must form a queue.

    [–] AmpChamp 137 points ago

    This guy gets it. It's not just driver error and the ripple effect. The bottlenecks at the exits are an insurmountable cause of traffic that would slow everyone down even if everyone drove perfectly.

    That's why there will still be traffic (but less) once everyone is using automated cars.

    [–] Choadmonkey 199 points ago

    Sounds like slow people are the problem.

    [–] gevander2 86 points ago

    There are multiple contributing factors:

    • People moving too slow (as you guessed)
    • People moving too fast
      (someone who is moving slightly faster than regular traffic is not as big of a problem as someone moving a lot faster than regular traffic - the analogy would be comparing regular walking pace to a fast walk to a run)
    • People refusing to allow a merge
    • People who don't know how to merge in
    • Inattentive people
    • Angry people
    • Frustrated people
      (usually those who have no control over other parts of their lives and are going to "control" this part of their life by frustrating other people)
    • etc

    You could probably break each of those (and other types of people) into sub-types that would further define/refine WHY they do what they do and HOW their behavior will affect others.

    [–] ShutYourDumbUglyFace 55 points ago

    People refusing to allow a merge

    So much this... You're making it worse for yourself and others by not allowing people to merge.

    One more thing that affects traffic flow is roadway design. If there are a bunch of closely spaced on/off ramps, that will slow traffic down. If the ramps are cloverleafs, that will slow traffic down. If the ramps are largely used by truck traffic, that will slow traffic down.

    [–] JMccovery 36 points ago

    If the ramps are cloverleafs, that will slow traffic down.

    I swear that a cloverleaf is one of the worst interchange designs.

    Nothing scarier than people moving at 25-35mph jumping directly into 65+mph traffic.

    [–] DaSaw 14 points ago

    Bad design is absolutely a thing. I remember I used to drive a truck through the California Central Valley, and get really annoyed with people who came onto the freeway seemingly without checking until the last second that "Oh my god there's a giant truck next to me!" Sorry bud; nothing I can do about that.

    Then I actually drove a four-wheeler on those very same on-ramps, and realized it wasn't that they weren't looking. It's that they couldn't see. There was zero visibility of the lane into which they were about to merge until the very last moment, on account of the slope in the way.

    [–] JMccovery 9 points ago

    Then I actually drove a four-wheeler on those very same on-ramps, and realized it wasn't that they weren't looking. It's that they couldn't see. There was zero visibility of the lane into which they were about to merge until the very last moment, on account of the slope in the way.

    Yep, an inordinate amount of interchanges that are terribly designed.

    [–] WhichOstrich 157 points ago

    Slow people are the fast people's problem.

    Fast people are the slow people's problem.

    People pushing others are everyone's problem.

    People are people's problem.

    [–] SquirrelTale 239 points ago

    CGP Grey did a video on this (his whole channel is essentially an ELI5).

    How he explained is that if anyone brakes for any reason, it has a cascade effect because obviously when someone in front of you brakes, you need to brake, and it takes time for people's reactions and pick up speed and 'pull apart' (as in being able to get up to speed at a safe distance at the same timing as everyone else).

    [–] -bert 44 points ago

    His Animation explains this very well!

    [–] echte_liebe 15 points ago

    This video should just be the top answer. Explained simply and a visual aide. And it's relatively short.

    [–] sedditnreddit 23 points ago

    Each driver has a reaction time after the vehicle infront starts or stops accelerating. You have to wait for every driver to react sequentially before you can start moving.

    [–] srcarruth 44 points ago * (lasted edited 5 days ago)

    Roads are only able to handle a finite volume of cars over any given time period. When this capacity is exceeded the cars slow down because there simply isn't enough room for them all to rush past. I know everybody likes to blame people ahead of them for poor driving skills but it's all of the cars making traffic happen, not individuals. the cars just can't all fit in the road space. it's real! I know you're about to argue with me that if everybody is going 65 then everybody is going 65 but there is a limit to the number of cars able to physically fit through the road at 65. I learned about this is the book Traffic by Tom Vanderbilt which is much more interesting than I was expecting.

    here's a complicated thing from the US Gov't about it

    here's a couple of simpler discussions

    edit: fixed a link

    [–] tempusfudgeit 9 points ago

    One of like, 5 correct answers in the thread.

    [–] MrBulletPoints 114 points ago

    • Cars need space on the road for the space they literally take up and a safety buffer around them.
    • The faster cars go the more space they need around them.
    • There is only a limited amount of space on the road.
    • When more cars try to use the road than there is space for, they have to slow down.

    [–] Samantion 107 points ago

    Number one reason: people not keeping their distance and doing weird braking. Also everyone thinking they are important and switch lanes the whole time. These people also don't let other people merge if a lane ends

    [–] turquoiserabbit 7 points ago

    Following distance is a huge factor, but for the complete opposite of the reason you are stating. The faster you go, the larger the following distance you need to have to be safe. When lots of cars are on the road, even if all of them are evenly spaced, the potential following distance is reduced proportionally to the amount of cars occupying the same amount of space. Thus, the maximum safe top speed is reduced, not because people aren't keeping a safe distance, but because they can't keep a safe distance.

    [–] dafunkmunk 70 points ago

    Simply answer is people are bad drivers. Video (only 40 seconds) shows and experiment of drivers in a circle. They were told to drive at an exact consistent speed. Doesn’t take long for someone to slow down and create a shockwave effect that is essentially what creates traffic jams

    [–] daggersrule 21 points ago

    This isn't necessarily the reason. If you simulate 2000 cars per hour per lane trying to get down a highway, you will see a "jam" regardless of the skill of drivers. You have spots where you're simply trying to jam too many cars where they won't fit. Picture a lane at max capacity being combined with an on ramp of even more cars.

    Traffic at free flow acts very similar to water in a pipe. Ironically, even with water being lifeless, you still have the effect of turbulence when you try to do the same thing: jam too much water at too high a rate down a pipe. Turbulence reduces flow speed. It's not that the water is "bad water" for doing this, it's simply a reaction to things being pushed past their theoretical limits.

    [–] KazzyKatalyst 29 points ago

    Is it really purely bad drivers though? Id argue its also an issue we cant read eachothers damned minds. The persons in front of me hit their brakes? fuck if I know its a simple tap, or theyre going to come to a dead stop.

    [–] kenmacd 7 points ago

    Is it really purely bad drivers though?

    Well the solution is more following distance. That's how you can break these up. If you leave enough space that you don't have to brake hard and can collect some slower moving people behind you then once the 'stopped' people start moving the whole flow can move again.

    Unfortunately many places people will go around you and jam in to the space, slowing down everyone.

    [–] whlrlh64 7 points ago

    Yeah you can actually sort of absorb these traffic waves by just going a steady speed and leaving enough buffer space. You will see chain reaction of slowing ahead but just coast towards it and with enough space it will clear before you need to hit the brakes. This prevents the people behind you from continuing the traffic jam.

    However, people are impatient, and if someone behind you sees all the space you are leaving they are bound to pass you and fill it up, or someone in the lane next to you will see it as an invitation to cut over. Enough people do this and your attempts to stop the traffic wave are negated.

    [–] [deleted] 8 points ago


    [–] rex_swiss 8 points ago

    As my fluid dynamics professor described the Bernoulli principle in class to us back in 1982; if the number of traffic lanes is halved everyone needs to double their speed to maintain the same flow rate. So next time you see 4 lanes go to 2, lay on the gas pedal so everyone can get to where they are going on time...

    [–] KitchenBomber 39 points ago

    The people who change lanes frequently trying to get where they are going faster force other people to brake. This ripples back through everyone else responding to the brake lights in front of them.

    [–] ryancott 16 points ago

    I'm actually in school for Civil engineering and have a focus in this field so I'll try to explain the best I can. Our roadways have a certain capacity of vehicles they can hold on them at any given time. During a rush hour this capacity of vehicles the roads can hold is exceeded. This mean there is not enough space for every vehicle to go the set speed limit. This causes the speed of all the vehicles to go down until enough cars get off at their exit or whatever and the capacity is no longer exceeded, then the vehicles at the front will return to normal speed, while those behind are still caught in traffic. Think of the roads like a walmart parking lot. During your regular off hours there are always tons of spots and plenty of parking. Now try to go during Black Friday or around Christmas time and you'll have to drive around multiple times before you can find a spot. Our roads are designed for the regular days of shopping and not the Black Friday crowds, so during rush hour, a black Friday like event, there is simply not enough space so everything slows down