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Most traffic jams actually act as a kind of compression wave moving backwards through traffic. Something as small as a squirrel running across the road can cascade into an hour-long jam.
One person brakes, then the person behind them, then the person behind them, but each time they are getting closer to each other (nobody stays equidistant from the car in front of them when braking). This causes a greater and greater slowdown as more cars are compacted into a tighter space, which travels backwards in traffic like a wave. Often the person who caused it doesn’t even realize anything happened.
A lot of mapping software actually estimates a given traffic slowdown by treating traffic as a fluid with a wave moving backwards through it.
That’s also why the best way to relieve traffic is to go at a slow even pace without braking. Every time the someone in heavy traffic runs up the ass of another car and brakes hard, or swerves into the “faster” lane and make someone else brake to not hit them, they cause another brake wave. If you have a few cars intentionally just hanging back and cruising with a big enough gap between them and the cars jocking for position in traffic in front of them, then their brake waves do not propogate behind you and eventually traffic just picks up pace again.
Edit: side bonus, you still get there just as fast, but with a lot less stress fighting assholes for position (minus the ones who fly past you thinking you’re the asshole for not riding someone else’s bumper)
Yeah, in theory it’s great but every time I try it people just cut in front of me then slam on brakes causing me to have to brake then adjust then repeat ad nauseam. People suck.
Yeah, maybe I’m fooling myself but it really seems like hanging back more makes me have to do more sudden braking. Traffic seems smoothest when I’m close enough to discourage cut-ins …. Even if that means Im more at the mercy of traffic in front flowing down a bit
But as a corollary, this is one of the reasons fewer lanes are sometimes better. A main road near me proved this out when they cut back from two lanes in each direction to one plus turn lanes. There’s no more jockeying for position, no more cut-in’s and you no longer have to protect your gap. Traffic is smooth and calm, and it improved accident statistics. Most importantly timing to get through that section is consistently better!
You need to give even more space then so that them doing that doesnt make you slow down. People cutting in front of you also helps because those are the assholes causing the brake waves.
Edit: down voters, I’m not saying that he “needs” to do anything as in it is his responsibility or he’s to blame. I’m saying that, if he is going to employ this strategy, that making room for pricks swerving in front of you needs to be part of that strategy in order for the desired outcome to happen. If they are making you brake, then your attempts will not work.
I have adaptive cruise with a settable car length and increasing the gap length just makes the cars behind you act more deranged.
I’ve found the only setting that doesn’t make everyone around me fly off the handle is the lowest (one car gap) setting.
I also drive in the diamond lane on long trips and typically have my upper speed limit set well above what the person in front of me is driving.
This is actually an argument for why these features should be mandatory. Traffic is caused by humans and their silly emotions. These types of self driving features with inter-communication would erase traffic jams.
At that point, you’re the guy doing 15 mph under the limit in the left lane.
Please only attempt this in the right lane.
Everyone is doing 15+ under. We’re taking stop and go traffic. What are you talking about?
Edit: Also the least effective place to do this is the right lane. The right lane can have traffic because exits are backup up onto the highway. The left lanes are the ones only getting backed up due to brake waves.
This is why I thought that maybe it would be good to have some kind of pacing cars, e.g. operated by traffic police? I.e. when you already know or can anticipate that there is a large jam building up, you bring in one pacing car on every lane at an appropriate low speed and everyone has to adjust, so the thing you mentioned won’t happen.
The problem with that is people would still do the same stupid shit behind the pace cars which would just cause the same issues.
The only way traffic pace cars would work is with better fundamental training (and enforcement of that training [meaning cops would actually have to regularly ticket people for tailgating]).
Especially here in the usa there are hardly any barriers to getting/keeping your license.
There is a massive amount of drivers who either shouldn’t be on the road at all or with heavy restrictions like not allowed to drive at night, not allowed on the highway, not allowed to drive certain classes of cars (kinda like other countries do for motorcycles because there is zero reason for any joe schmoe to just be able to legally get behind the wheel of something like a supercar on public roads)
Nah, cops being on the highway is one of the big causes of traffic. Everyone slows down to the speed limit when they come up on a cop and many are too timid to pass at all. This causes a huge brake wave and fucks everything up. It’s why I don’t think speed limits should even be a thing or should at least be adjusted because most highways are so low that just about everyone ignores them (and is not harmed doing so) until law enforcement appears. If people want to go slower that’s fine but they need to keep right when they aren’t passing and everyone needs to leave plenty of space in front of them so that traffic is permeable enough that people can get to their exit without causing brake waves and absorb the “shock” when it is necessary for someone to hit their brakes.
This is about 2 decades old now but a bunch of people tried something sorta like a pacing car https://www.youtube.com/watch?v=OoETMCosULQ
Or we could just build trains and other alternatives to cars, which would end up cheaper, faster, safer, environmentally friendly, …but we have big oil.
(Sry, I had to)
I feel like regular patrol cars might work like this already - who’s going to blow past a cop driving down the road?
me, because i know what speed they’ll pull me over at and if they’re doing 20 under that, who cares
I feel that
Works for me even with cut ins, gets easier with practice I’d say! Couple interesting YouTube videos on it, one here:
Then leave another gap. There are finite idiots in the world, and you cannot actually go backwards.
Nicely demonstrated here: https://youtu.be/Suugn-p5C1M
I couldn’t even see the traffic start because the fucking “Related Videos!” popups. God I hate what youtube has become.
Right, if you think about the creation of traffic as a negative speed wave which causes compression, and traffic alleviation as a positive speed wave which requires rarefaction, then it becomes clear why traffic is so stubborn. When people are so bunched together, no positive speed wave can propagate. Which is why you literally get to to the point where the original idiot slammed on the brakes and the traffic magically disintegrates. If everyone stayed 5 car lengths apart in traffic, that alleviation would actually propagate backwards as fast as the initial congestion.
Preach truth, Krypty
Adaptive cruise control FTW. Matches speed with the person ahead of me (up to the max that I set) and maintains a gap that I can specify. It starts slowing down long before I’d notice the gap closing if I were doing it myself, so the +/- acceleration is a lot smoother as a result.
So, I don’t know exactly how the adaptive cruise control works. But if it is slowing down and speeding up to maintain a specific distance, that does not fix things. The idea is to maintain a specific speed such that, as the people in front of you accelerate and brake, speed up and slow down, you have enough distance to not have to do that. You should essentially match their average speed with enough gap that their braking doesn’t put them close enough to your bumper that you have to slow down yourself. Normal cruise control would be better (except mine won’t set at speeds under, I think, 20mph) because your speed wont change. Adaptive cruise would make your drive safer, maybe, keeping you from being too close or failing to react to the change in traffic speeds, but I dont think it would solve the traffic issue itself.
You aren’t solving traffic as an individual driver anyway. Sorry to burst everyone’s atomized bubble here but that’s complete nonsense.
If you manually maintain a large gap in front of you, everyone behind you becomes complete weirdos.
We could “solve traffic” by not requiring single occupant car drives to accomplish everything in our daily lives.
You’re quite literally incorrect and talking out of your ass
You’re right of course, the reason traffic exists is because you, DancingBear, cannot be on every roadway in America at the same time.
Seriously dude, have you ever been in traffic? I’m not talking about a small slowdown on a one, two lane, or even four lane road. I’m talking about sitting on the 5 or the 101 in any of the multiple times it becomes a parking lot daily.
Manually maintaining a large gap in front of you is not solving that shit, and it’s frankly ridiculous to suggest that it will.
Keep beating your straw man I guess
It’s not “locked” to a specific distance, it’s fairly elastic and the exact follow distance varies based on speed. So, if traffic slows down, it will gradually close the gap while also slowing down. The end result then is far less drastic speed changes.
Californians te the worst drivers in the world because none of them understand this simple concept. Every day I’m driving, I give more than enough space in front of me for someone to cut me off and I don’t have to brake. It’s simple. However, I’m constantly getting people riding my ass. Switching around me. And being over all menaces just because I’m leaving a roper gap between myself and the car in front of me. It’s wild.
When idiots ride my ass I slow down.
Im driving the speed limit in the right hand lane and you ride my ass - I let off the gas to the minimum speed (here its usually 45mph)
Im actively passing in the left lane and you ride my ass I let off the gas.
When the idots back off I speed back up. If they start riding me again I slow back down. After a few times of this they usually pull their heads out of their asses and back off/ properly change lanes.
huh, they seem to get that concept on the highways i drive on. big state though, we could live ten hours apart from each other.
Haha true! I’m talking about Southern California. Los Angeles and Orange County.
You think drivers from your <country/state/city> are bad? That’s because you have never driven in my <country/state/city>
In one of the Mission Impossible movies Tom Cruise is supposed to have a boring job no one will ask him about and the movie shows this by having the character talk about traffic patterns. I thought it was interesting information then and think it is interesting now.
It’s a great cover story until he meets someone at a party who loves that shit.
It’s kind of funny. The writers probably thought traffic pattern analysis is boring because everyone hates traffic. Actually traffic pattern analysis is interesting because everyone hates traffic.
Lmao I remember seeing this exact scene as a kid, thinking as he was talking “oh that sounds cool as fuck” and then only from how the scene played out realizing it was supposed to be a significantly boring concept
Do you know of a paper that describes this kind of traffic motion?
Here’s the (abstract of the) paper I was thinking of https://pubsonline.informs.org/doi/abs/10.1287/opre.4.1.42
Appalling that I can’t find a free version of a 70 year old paper. You might be able to find the full text somewhere… I would of course never encourage anything that might run afoul of the scientific publishing protection racket.
I couldn’t find the paper I was thinking of that described the phenomenon of traffic propagating as a pressure wave, but I did find this paper (new to me) that describes a model for simulating how congestion spreads in urban environments (as opposed to an isolated highway, which IIRC the paper that most people reference models). It does have the full text available though, and it looks like a good read and has references that should get you going on the history of congestion research.
I am not an expert; I just found this with a few minutes of searching. If there are experts with better papers I’d be happy to hear from ya!
I knew about the elastic band effect, but I was unsure if it was considered the same. But searching that I found about both:
The Mythbusters did it! They couldn’t even get up to speed to begin the first experiment because the traffic jam formed naturally.
Hm, this video isn’t available in my country.
Only ever have to ask, my friend
Heres an overview shot of a traffic pulse.
One person brakes for no reason which leads to everyone else braking. The pulse travels despite there being nothing there. The longer it can take for someone to start up again also can delay the whole thing.
It happens when people tailgate. They over react and it causes an accordion effect.
Or when people drive too aggressively and cut someone off, causing the person being cut off to slam on their brake.
Iirc, the answer is to have someone drive slowly and let other cars pass. It creates a buffer zone that regulates the flow back to normal pace. Or at least that’s what I remember from New Scientist’s video from like a decade ago.
I used to just idle when traffic moved. Slowed down way before i was even close to the car ahead. Played a game where i was trying to move at a constant speed or max fuel econ. Much less stressful to always be moving than gas/brake every 10s, even if you’re moving 5mph.
Really helps to look 3-4 cars ahead for brake lights.
not slowly, just leave room
Nope that’s just a negative picture of a guy
A few years ago, I was bitching and moaning about a jam, and my pal just said “you’re not in traffic, you are traffic”.
I know it’s nothing more than a cheeky soundbite but just reframing it like that and knowing I’m part of the problem rather than the exception has made me a lot calmer on slow moving roads.
Plus it has encouraged me to either use public transport more, or just drive to a park-and-ride a mile or three out, and run the rest - facilities permitting of course.
“No John, YOU are the traffic!”
And then John was traffic
Traffic John is what they called him.
Johnny Jam to his mates, or J-Traffz to his record label.
Yeah that was a through the matrix moment for me too.
I still lose it when I finally get to the front of the jam, and the only reason for said jam is because everyone is stopping to look at an accident on the OTHER SIDE OF THE HIGHWAY.
Yeah, it’s frustrating.
I’m not entirely sure what the rubberneckers want to see either. “Oh look, someone critically injured next to someone who is likely deceased”, because that isn’t a day ruiner at the best of times.
Odd.
Switch to a motorbike, then you can experience righteous anger at the handful of drivers slowing down hundreds of bikes and people in buses.
Funnily enough, I’m planning on getting my licence at some point.
I’ve no interest in motorbikes, I would just love to learn how to ride one safely.
I understood them as expensive toys, like an old Italian project car that’s fun to tool around in in nice weather, but when you need to get to work, you drive your car, but experiencing its role in SEA completely change my perspective. They can be cheap, boring, functional machines, with a suprisingly high capacity. that even a dog can perform basic maintenance on and keep running for decades, that work just fine in rain.
Good shout.
I live fairly rurally and the roads/drivers don’t really lend themselves to new riders.
I think if I lived in a big town or city though, I’d absolutely pick up a chicken chaser and rattle about short distances on one, they seem to be perfect for that sort of use case.
Plus, not that I’m a huge fan of tobacco advertising, bikes in the Rothmans livery look absolutely stunning to me.
This is like saying you don’t know how a bottleneck works.
Exactly, it’s entirely because the people in front of you are going slow.
99% of traffic like this is caused by people following too closely.
Yeah ideally you put 3 seconds between you and the car in front of you. Gives a nice, springy cushion to not brake as much. Your mechanic will also be surprised how much longer your brakes last.
I’ve always said that if you’re using your brakes on the highway and it’s not for an emergency stop, you’re too close to the car in front of you. Even if they’re the type that are on and off the brake constantly, if their speed isn’t changing much you shouldn’t need to follow their example. Of course I try to get out from behind them because they are like crying wolf and one of those brakes might be for real.
When caught in a traffic jam I look for a semi to get behind. They won’t accelerate fast like some car drivers do, and they don’t stop as fast either. Plus they can see better if things area really starting to move or not. Keep a few car lengths behind them and while everyone is doing the start and stop motions, I’m keeping a slow but steady speed usually without needing to brake at all. It’s also less stressful.
I don’t always hang out behind a semi when just doing daily driving, but I will 100% camp out behind one when pulling my trailer - massive fuel savings from reduced wind resistance.
It’s a joy to go an hour using a release of the gas pedal as the “brake“
If you’re in traffic (i.e. if you are part of the traffic) and you leave a 3 second gap between you and the car in front of you, another car will drive into that gap. If you back off to create another 3 second gap, it will happen again. Even worse, if you hit the brakes to create that three second gap, even if it’s very lightly, you might cause an even worse traffic jam behind you.
I would prefer to leave a big gap to the traffic in front of me, but in many cases 3 seconds simply isn’t practical. A car merging into the lane in front of you is inherently more dangerous than a car already being in that lane. If you keep trying to maintain a 3 second gap in heavy traffic, not only do you put yourself in more danger as you keep having cars merging in front of you, you also cause more danger to the drivers behind you by constantly backing off or braking to try to maintain a gap.
It would be absolutely wonderful if everybody believed in the 3 second rule. Traffic would flow so much more smoothly. But, apparently that isn’t human nature. And, if you keep fighting for that gap when nobody else believes in it, you can actually make things less safe for yourself and for others.
If you’re still moving with traffic, why do you care that someone got in front of you? If you’re slowing so much that lots of people are getting in front at one time, then you’re the obstacle. A 3 second gap changes with speed, if it’s slow traffic that’s less than a car length. And if some asshole muscles their way into a gap unsafely, let them. You’ll still get to your destination far faster than if you hit each other or cause some road rage stupidity because of who is in front.
Driving brings out the worst in people for no gain at all.
If you’re still moving with traffic, why do you care that someone got in front of you?
Because you no longer have a 3 second gap so you can no longer safely react to something happening in front of you.
If you’re slowing so much that lots of people are getting in front at one time, then you’re the obstacle.
That’s my point. If you keep trying to make a 3 second gap and it keeps being filled in, you’re going to cause a traffic problem.
A 3 second gap changes with speed, if it’s slow traffic that’s less than a car length
Technically, sure. If you’re driving at less than 5 km/h and people on foot are passing you, then yes, you can have a 3 second gap with less than 1 car length. But, if you’re driving at less than 5 km/h are you really driving, or are you effectively stopped in traffic?
If all these people are merging in front of you, then the adjacent lanes are moving a lot better, which is helpful for traffic. Less braking is the goal, and if 2 or more lanes aren’t braking as much because you left some space in front of you, then traffic should flow much better.
“if you leave a 3 second gap, there will be enough space for others to safely merge into that space as they need to”
And after they do, there will no longer be a 3 second gap, and you’re now driving too close to the person in front of you.
You don’t have to brake and maintain a hard 3 seconds between gap. Just let off the gas a bit let it slowly restore itself. That gap is there so cars can move in and out as freely as they need.
Depends on how aggressively someone merges in front of you, and what they do once they’re in your lane. Some people will merge way too closely. Some people will merge then slow down suddenly. Sometimes you do need to brake.
If they merge in your lane and then brake, then thats on them, not you. Yes, you will have to brake, but its not you that is being the bad driver. Just create more space between you and the car in front of you again.
You could also look into merging into a different lane temporarily until space is restored.
Too many people were taught, and still teach, the “two car’s length” rule. Which is awful. 2 to 3 seconds is much better and intuitive to figure out.
You say 3, which is great, but I’d settle for 2. Most people on the highways around me leave more like 0.5; I sincerely think the vast majority of people greatly overestimate the amount of space in front of them to the next car.
Two car lengths is ridiculously close. The average car is approx. 4.5m in length. Two car lengths is 9m. The average human reaction speed to visual stimuli is approx 250 milliseconds. At 100 km/h (28 m/s) you would travel 7 metres in that time, and that’s just the time for you to notice the stimulus and react, not to choose an appropriate action. If you’re 2 car lengths behind and the car in front of you brakes hard, you’re going to hit it.
2 seconds behind is 56 metres behind, or 12.5 car lengths. 3 seconds is 18.5 car lengths. Even 0.5 seconds is 3 car lengths. Not enough to safely react to the car in front of you doing something unexpected, but not the tailgating that 2 car lengths implies.
3 fucking seconds
The answer is a simple 3 second gap.
That’s it, just 3-mississippi (or 3-onethousand) seconds behind the car in front of you and most of the avoidable jams go away.
If you do that, someone will move into the gap. If someone moves into the gap you can slow down to make another gap to them, but then someone else will drive into that gap. I don’t know of any major city where you can maintain a 3 second gap during rush hour.
Even worse, if you ever brake to try to create a gap, you’re likely to cause a traffic jam behind you.
Sure, if everybody did follow the suggestion and allowed a 3 second gap you wouldn’t have traffic jams, but that’s just not human nature, apparently.
Teach people to drive on the right lane unless they want to overtake somebody. Whoever overtakes you on the left won’t drive into the gap because they also want to overtake whoever is driving in front of you.
It’s too late to teach the entire population how to drive differently now.
You attribute an uneducated, uncivil approach to human nature, but I have been in human queues around the world, and they vary hugely based on cultural and social differences.
What you think is human nature seems to actually be driving culture in your region.
Yesterday I had a swasticar driver actually let me in on a disorderly merge. I was amazed, it was a first. Clue: nothing about Hondas changes people to be better. Tesla and BMW drivers are just shittier at sharing. This is culturally allowed.
You’re totally right. It’s a social/culture issue. You doing this on your own isn’t going to do shit. Everyone has to miraculously decide to come together to solve the problem with no one taking advantage. It’s the same reason we can’t do anything about climate change.
Edit: I realize this came off as extremely dismissive about climate change. I still think we should do what we can to, at the very least, reduce effects. It was more just a realistic take of why I think we’re all fucked. I still avoid eating meat, single use garbage, and other wasteful shit, don’t get me wrong.
Can anyone tell me why this is being downvoted? I don’t really care about downvotes, Im more just wondering how I’m wrong.
At least with climate change, your actions can make things slightly better. It’s not enough to be measurable if only one person does it, but if it’s a tiny pressure in the right direction. But, if you drive in a way that’s too different from how other people drive, you can actually make traffic worse or more dangerous.
Except the person next to you or behind you gets frustrated and cuts you off and you have to hit the brakes and create a traffic pulse.
Well yes, society functions only with cooperation. Uncivil behaviour ends with violence and dismay.
However 3s usually allows for slow adjustments which alleviate caterpillaring.
CGP grey did a video on it: https://www.youtube.com/watch?v=iHzzSao6ypE
Basically one car breaking too much will make the following brake even more and so on until one stops and there’s a jam. There is no clear reason like a road blockage or an accident, just compounding slow down.
Basically one car breaking too much will make the following brake
If the car in front of me started breaking, I’d definitely get out of the way.
I’d recommend this video as a response to that one, cgp greys video is technically correct and fucking dumb at the same time
The people at the front are morons and probably in the wrong lane.
You don’t like driving 55 in the passing lane? You get such a great view of everyone flipping you off!
It all starts with someone in the passing lane, not passing, and one or more pissed off people behind them :)
The pissed off people trying to get around causes the wave of people behind them to brake and it snowballs from there.
Yeah I drive around 3 hours on the highway every several weeks. Sometimes on my drive, there’s obviously traffic. A lot of times it will be something like rush hour traffic, a crash, construction, etc.
But then like…a good portion of the time when I come to the very front of the “clog”, I find that it is just a blockade of multiple people going incredibly slowly and taking up all lanes of traffic, refusing to move over despite the fact that they are going under the speed limit.
People drive too close to each other, someone has to slow down and then the car behind slows down a bit more. Repeat until you get to the point someone completely stops. Then the next car stops for slightly longer.
If you leave a safe distance then it wouldn’t happen.
It’s usually a complex crowd effect created by many participants trying to maneuver among each other in slightly disperate ways.
In Portland OR, it really is because some dingbat slowed down to 20 MPH on the interstate for literally no fucking reason at all.
Often they do this because their car is barely limping along and they are trying to make it to the next exit.
This driver is distinct from that driver. We definitely have those too, and they have my sympathies. 10 seconds of engine death vs 10 seconds of brain death.
Taking I-5 into Vancouver from Portland is always horrific. Once you get over the bridge it always clears right up! A big part of that is all the on ramps. There’s so many of them! So everybody is having to make way every 10 feet for someone merging in.
It’s horrendous.
Yeah they could probably stand to lose the more southern of the two ramp sets at Delta Park, feels very extra and overall unhelpful (And I say this as someone who uses that ramp when headed north). Of course ODOT’s solution, beyond replacing the bridge, is to widen I-5 south of the bridge - Which anyone with a brain and 50 years of highway traffic studies can tell us would directly contribute to worsening the problem.
Its because of two things. One is that people hog the passing lane or try to pass slowly so it takes them a few minutes to overtake a few cars, and also because people drive at different speeds. Some people drive at the speed that feels comfortable, others drive the state imposed speed limit. This creates pockets of dense traffic, and then people try to pass, but there is always the person who tries to pass as slow as possible because they are going a few mph over the speed limit.
Its really just a bad combination of laws, and drivers who are terrified of breaking the law, and people who dont know how to drive correctly in a way to reduce traffic. Also many people are just never consider that others also need to use the roads. They don’t care about traffic. Some people also have health issues, like blindness, or mental handicaps, which means driving at interstate speeds is about all they can muster.
Hey, if you have some physical limitation and cannot or are simply not comfortable going faster, that’s 100% fine (assuming you can operate a car safely). Stay the hell in the right lane and never leave it, thanks
https://www.mdpi.com/2076-3417/11/9/4278
TLDR: modeling traffic as a gas leads to fairly accurate predictions. If that doesnt mean anything to you, here’s a decent visualization of how gasses move around in a system. In this analogy, each of the gas particles models a car on the road. https://youtu.be/Hr5Baj3lXFA
