So let's quote the author:
"The important fact: there is a limit to the number of cars that can pass by a given point on the highway in a given amount of time, and that limit is one car every 2 seconds, per lane. So imagine you are in heavy traffic during rush hour. There are a certain number of cars in line in front of you. Let’s pick a point on the road to call the front of the line — say, the point at which you plan to exit the highway. The line gets shorter by one car every 2 seconds. If there are 1,000 cars in front of you, it’s going to take a minimum of 2,000 seconds for you to get to the front of the line. It doesn’t matter whether people are kind and let cars merge in front of them, zipper-style. It doesn’t matter how much stop-and-go there is. The simple fact is that it takes 2 seconds per car for you to get to the front of the line, and there are some cars in front of you that have to get there before you do."
Ok this is correct. BUT: I don't care if it takes me 2,000s if my exit is 44 miles away (80mph) but I do if my exit is 10miles away.
So you drive along at 80mph and there is cars around you everywhere. Do you care? No, you're covering distance. It's the same as if you were all by yourself on the highway. The distance between cars is absolutely irrelevant and so is the time between cars if you still go 80mph. Nobody would call it a traffic jam.
Next quote:
"Leaving space in front of your car for people who are trying to merge won’t solve anything."
Yes it absolutely does. And it again solves one very very important piece of a traffic jam: Average speed. Leaving space is crucial. It allows people to do two things:
- Accelerate
- Not having to brake
These two are crucial to get speed up and thus resolve traffic jams. Incidentally he linked an article which visualizes exactly this:
http://www.smartmotorist.com/traffic-and-safety-guideline/tr...
(Section: Merging-lane Traffic Jams, A Simple Cure)
You can see on the right side how his "cars per second" is _exactly the same_ than on the left side. Yet, everybody will be much happier on the right side. Why? Because the speed's been increased and people in the cars cover ground.
Next quote:
"Suppose you’re on a 2-lane (each way) highway and one lane is closed up ahead due to construction. Now the flow rate of your lane is cut in half (or there are twice as many cars in line in front of you, depending on how you want to look at it). Road signs commonly ask you to use both lanes up to the point of the bottleneck. That’s reasonable advice, but it’s not going to get anyone home faster"
Yes it absolutely does. Why? We are all programmers here so let's talk in our lingo: This is our API. Our interface that we agree on. If people follow the interface (rule), then we have people agree on it and we are predictable and prevent braking. This is exactly what we want. Increase speed (with gaps), prevent breaking, be predicable. No surprising cars merging means no breaking and thus increase in average speed which in turn means no more traffic jam.
Please, disregard this article. The conclusions are wrong, the assumptions are wrong and the deductions and the terrible advice he gives at the end is wrong.
But it does not make people go home faster. Let's put a simple deductive thinking practice:
If you are the first car in the jam, you are stopped and slowed by traffic lights, police, accidents or whatever, but the traffic jam does not affect you, you are going as fast as you can.
For the second car, you will not get to your destination faster than the car you're following. So however you drive, you will not be faster than following with minimal distance.
The same applies to the third car, and on ward.
Basically, the fastest way to get through a traffic jam is to follow closely, and that means stop and go.
IF your model is correct, the traffic jam will clear since everybody will at some point reach their desired speed of approx ~80mph again. However, the reality is differnt. The model doesn't work since people break. That's the thing that makes your "deductive thinking practice" break down: People break. To prevent this....
Wait, let me just link this:
http://www.smartmotorist.com/traffic-and-safety-guideline/tr...
You are describing a particular greedy algorithm wherein each individual car gets home as fast as they can. 1) Car #1 gets home as quick as they can by following closely. 2) Car #2 gets home as quick as they can by following closely, given #1. 3) Car #3 gets home as quick as they can by following closely, given #1+#2. ... Yes, given 1..N, the course of action which minimizes your own time is to follow closely. I agree. And people will probably act that way.
But that doesn't make it an optimal solution. Consider that car #1 introduces several seconds of delay due to braking and acceleration. Then car #2 does. Then car #3. By the end, you've got hours of delay built-in.
Optimal is obviously hard to define. But most people would agree that it's not every driver maximizing their personal interests to a globally shitty end. Everyone following closely is the prisoner's dilemma where both betray each other.
Consider the following alternate thought experiment. Flow of traffic is very much non-linear. That's what stop and go does -- it introduces cascading delay where there was none. Suppose roads are just 10-15% over capacity, and it results in a global average commute time of 1h instead of 45 minutes. This is not unrealistic. What if every day, 20% of drivers leave 1h later, thus preventing stop and go and keeping commutes to 45 minutes. Even if you counted their extra hour as commute time, the average is still less 1h.
I'm not saying this is a good idea (though strategies like this have been used in some cities). I'm just saying that are ways to get everyone home faster than everyone maximizing self-interest [co-operative self-driving cars please!].
Quote:
"The difference between these is negligible at high speeds, but at a low enough speed, it becomes difficult to maintain a 2 second following distance from the front bumper of the car in front of you without impinging on the rear bumper of the car in front of you, especially if said car is more than 0 feet long. So under these circumstances the flow rate of the highway decreases below 1 car every 2 seconds — maybe to 1 car every 5 seconds. So now you have to wait 5 seconds for every car in front of you in line."
There you have it. We have plenty of space/time to play with in case we're in a traffic jam since we approach very very slow speeds.
Obviously I'm not saying you should stay 10ft behind somebody when going 80mph.
--
First we must assume we live in the 3rd dimension of a physical realm, wherein objects like cars cannot pass through other objects. Cars can not drive through other cars, thus, if one car stops or slows down, all cars behind it stop or slow down.
Second, 5000 cars cannot travel 65mph over one mile of road, because it is physically impossible to fit 5000 cars inside a one lane 1-mile stretch of road. This is the bottleneck that causes the initial traffic jam.
In order to get all 5000 cars to travel the distance of a mile in the same TIME as 1 car, your only option is to increase their speed. But our speed is limited (by the speed limit of the road), so the only thing we can do is squish them together and hope for as fast a speed as possible given the dimensions.
If all the cars were linked and communicated in unison, they could react immediately and maintain a high degree of coordination in moving around each other and traveling as fast as the number of cars and speed limit will allow over a given area. Unfortunately, humans suck ass at driving, and their communication and latency make the movements of cars much much slower than is theoretically possible.
--
So what does "leaving space" actually do within our constraints of number of cars and max mph? It smooths out the errors humans make in driving. Specifically, it adds a time buffer for communication and decision-making; more time is given to driving decisions in order to prevent unnecessary stops, which would slow or stop the cars behind it.
What "leaving space" does NOT do is change the laws of our physical world. The given number of cars still have a maximum possible speed in a given distance, due to the traffic laws and physics.
Is it possible that the buffering from leaving space in the road will cause traffic to actually move faster than the starting-and-stopping of human error? Yes.
But it also uses up additional space, which is equivalent to more cars on the road, which as we know from above means a lower speed to travel the same distance.
--
You can not get away from it - until you reduce the number of cars or increase the max speed, your traffic jams will remain.
As for my personal opinion, I believe the one thing that could reduce traffic slowness is to speed up merges. If you want to help a traffic jam, merge at a speed faster than the cars around you and accelerate away from the merge area. It won't permit more cars on the road, but if a car is going 45mph and you move in front of it going 35mph, physics only allows for two results: the car behind you will hit you, or the car and all the cars behind it will have to slow down to 35mph.
The other thing that could be done is sensors in the road could detect the level of traffic (number of cars) and provide on a digital display the maximum speed humans could manage for that many cars on the road. If all cars then traveled at that speed, we would slowly but at a continuous pace travel down the highway without any stops. Until the first asshole that merges slower than that speed, which would make everyone slow down to his speed, defeating the whole thing....
I'm sorry if my post was confusing. I didn't really mean to go to infinity with my theory. I really only wanted to point out the flaws of the article. I didn't mean to say that traffic jams can be avoided. I simply disagree heavily with the author and agree with what's been out there in traffic theory for decades. Part of what you described well in your post!
Again, I'm not suggesting anything radical or want to emerge a new theory. The existing ones are good. I'm just trying to point out flaws from the OP.
People who pick the wrong lanes can change back immediately and travel the right way rather than either (a) slowing to a crawl with their indicator on hoping to be allowed into the correct lane by some kind soul (who also has to stop/slow down) or (b) looping back round on themselves and trying again.
Obviously, both of the latter solutions add to congestion, and the most common solution I see is an awkward combination of both (a) and (b).
EDIT: In addition, smoother-flowing traffic is desirable in-and-of itself, as fuel economy is greatly improved.
Is it my browser, or is this completely wrong? For me, the right side moves about double the amount of cars into the upper edge of the image. And I believe that this is the point of the section — it wouldn’t make any sense otherwise.
Yes, but there are way more cars on the left side. That is the difference. Occupancy (density) determines speed when flow rate is fixed, and that graphic is actually a perfect illustration of this. You can't make the cars on the left travel at 80mph because it would not allow for a safe following distance.
One thing that is the same on both sides is that if you're the nth car back from the merge, it's going to take 2n seconds for you to get to the merge. Yes, the important thing is how many miles you can cover in that time, but this way of thinking places an upper limit on how many miles that can be, based on the occupancy of the road.
Also, pretty sure the advice at the end was tongue-in-cheek ;)
I hope you keep it up and maybe have a follow up post where you can fix some of the flaws.
Some of your ideas are correct and noble. But always remember to take into account the real world driver and his/her behavioral flaws.
Few thoughts: Interesting would be a stochastic behavior model of drivers + driving strategies and in connection with red lights, accidents, rush hour to see what happens. Thought, that model would be quite some work in python.
Cheers
The free flow merge theory applies only in open areas with maybe temporary blocks that flow is unrestricted in any other way.
The no-merge theory applies on situations with traffic lights (and/or other special flow control such as a policeman or toll booths etc) where you suppose there are cut-off points that allow a specific number of vehicles per second.
It also runs counter to what is commonly said about traffic jams. Most people focus on restoring smooth flow by doing things such as driving really slow to create space in front of you. This guy makes the case that "flow" is not really the important factor here.
For the record, I am "that guy" who runs all the way down to the end of the closed lane before merging over. Except I don't consider it an asshole move because as OP points out, I'm making the best use of the road ahead (while allowing fewer people to merge ahead of me)
In interstate travel I have noticed the increasing frequency of the "two trucks" maneuver, in which a big rig driven by someone philosophically opposed to your habit will drive in the "closed ahead" lane directly alongside another big rig in the "open but crawling" lane. Once the two trucks near the point of obstruction, the "open" driver is happy to let the "closed" one merge in, and there is no merging at the point of obstruction, which is both a safety and traffic-flow win.
I contend that the two truckers have done more to speed actual traffic flow (i.e. from a point before the obstacle to a point after it) than any number of assholes have. While at the beginning of the maneuver there is a solid line of fuming assholes behind the "closed" truck, by the time the obstacle has been reached all fuming asshole traffic has completely merged behind the "open" truck. Since it is only merging at the point of obstruction that slows traffic more than the obstruction itself already has, this is a net win.
Of course this maneuver must be repeated by successive pairs of truckers, and occasionally an asshole will "win" by racing forward between pairs, but that's minor.
Which of these rules applies to cars merging? There isn't a set standard, so people invent their own and perceive their rule is universally understood.
Doing this is like saying "Hey you idiots, look how smart I am" to everyone waiting for their way in the right lane.
The lane is open until it is not, and as long as both lanes are open they are both "right" (in the non-directional sense, obviously). Why rely on clearly nebulous (sometimes variable, sometimes non-existent) social norms rather than concrete traffic norms? Use the open lane, or don't complain when others do. It's not asshole behavior, it's common sense driving.
There is no reason to take offense while driving so long as people 1) follow the rules of the road and 2) do not endanger others with reckless driving. Using open lanes does neither, and it only inconveniences the people that refuse to use the roads as they are intended to be used.
This is true of unstopped vehicles as well. Not everyone is comfortable driving at the maximum safe speed. In fact, where I live, fines are enforced on all state roads from 6 to 13 MPH below engineering guidelines. Even so, many people choose to travel even slower than allowed by graceless statute. While these patient souls approach the bottleneck, several of the swift may de-queue themselves to the benefit of everyone who would otherwise wait behind them.
Oftentimes, the road hasn't actually reached saturation--it's just a compound case of live-lock and if people use the full measure of available lanes (instead of stopping at the first sign that says "Road Work Five Miles Ahead"), they have a greater opportunity of resolving the contention without promoting a cascaded slow down.
Of course, all of this is an edge-case. As the OP alludes, when the road is actually saturated, the real solution involves either decreasing demand for or increasing the supply of throughput at the chokepoint. Mere bickering and maneuvering will not avail anyone.
Please keep that line as short as possible by using all the lanes available.
What really piss me off are drivers who move from the "right lane" into the "open lane", and then merge back after cutting perhaps 5, 6 cars.
Which solves nothing but to piss off everyone else behind you who has waited because ultimately someone will let you merge in (which they flat out shouldn't) and said behavior will only encourage others to do so in the future which inevitably will piss off even more people.
Asshole move? I don't understand. I don't live in the US, but here it is encouraged to act like this! It's called a zipper merge. I remember public messages on the TV encouraging this behaviour, and there's road signs near merging lanes.
What's so asshole about this?
It's not like modelling traffic is so insanely hard that we need such simplistic models. Pick as complex a model as you like; we have the computing power to simulate it!
Up next: why F = ma really, really matters for space launches. Experts don't know this!
Yes, there is too much rambling for making a point, yes the tone of title is quite arrogant / link-baity.
But this terrible essay did prove the point: smoothing the wave is not going to make you go faster.
I think he fell down on his own argument when he claims that doing that causes a "big traffic jam" downstream of you; how can it, if you're only 10 or 20 seconds max further behind than you otherwise would be? You can only cause that much additional "traffic jam" in the back, and it may well be worth it to create a more laminar flow.
It utterly fails to explain the extreme variance in real traffic throughput during congestion. The original article does.
It's also more fuel efficient.
From the article:
>Suppose you’re on a 2-lane (each way) highway and one lane is closed up ahead due to construction. Now the flow rate of your lane is cut in half (or there are twice as many cars in line in front of you, depending on how you want to look at it).
What I observe is that the speed is reduced to one twentieth of the speed, not just half. This is because people are merging very slowly while jostling resulting in needless braking. If everyone could agree upon a proper zipper merge, the speed for everyone would go up many times.
Or imagine a traffic signal at the merge point that only lets one lane go through for a minute each. The overall flow rate would be much higher than what it is without such a signal.
Discounting this based on theoretical flow rate (as if removing one lane reduces real traffic flow by only 50%) shows that the author totally ignores real traffic scenarios completely at odds with the title of the article.
You are dealing with a queue as well as a through-rate at the merge-point. The through-rate with one lane can still be 1/2 of the through-rate with two lanes, but because you have a queue waiting to reach the merge-point you can end up waiting much longer. More spacious merging will not change this because of the principle stated in the first paragraph of the article.
Increasing the speed at the merge-point will not decrease the queue. It will only decrease the density of the queue but move it back further in traffic. Your time to cross the merge-point will be basically the same.
However, on a congested road very small changes can have huge effects. IIRC, one study showed that a 1% decrease in the number of vehicles resulted in a 28% decrease in commute time.
EDIT: For all you infra folks out there, imagine not being able to dynamically provision resources, no packet loss and worse, the packets can basically do what they want. That includes things like crashing into each other and stopping any other packets from making it through.
Am I missing something about what the author is saying about the empirical data?
The stark uniformity of the empirical data up to the congestion threshold compared to the wild variance in heavier traffic is exactly the point of the older article this author is critiquing. Of course congestion happens when you approach capacity. This article is rejecting the original's explanation of that variance, without offering any new explanation.
'WOW! REALLY?'
> At low occupancy (cars per mile), drivers can go as fast as they’d like. As occupancy increases, so does flow rate, even though speed decreases somewhat due to everyone trying to maintain following distance. At a certain point, when occupancy becomes high enough, speed dips low enough to where drivers are unable to maintain their minimum following distance, and — catastrophe! — the flow rate decreases dramatically.
On every highway trip I see countless cars camped out in the left lane but moving at the same rate as the rest of traffic.
One should only use the left lane for passing. Otherwise, stay right.
Traffic flows smoothly when people follow this system.
In many places this is the law, rather than just ettequite. :)
Of course, that doesn't mean people actually stay right unless they're passing.
The prisoner's dilemma also applies to this. Behavior that is "optimal" for a single individual in terms of getting to destination is not what's optimal for the collective in terms of safety. And optimal behavior for getting to destination is not the optimal behavior for safety or lower stress driving, either.
I agree that the optimal behavior isn't universal though. One example I'd cite is that I always leave more space when the vehicle in front me is so big that I can't see what's in front of it since that limits my reaction time to what that one vehicle is doing rather than what's going on further ahead.
Recently, I've tried to perform a few basic hypermiling techniques, especially "timing a light": if I'm the first car to encounter a red light, I leave extra space and can sometimes be moving through the light at 20mph or more when it turns green instead of stopped. It seems analogous to leaving space in front of you during a traffic jam, so that you can exit the jam at a faster speed.
The problem with this is that other drivers will often take advantage of your behavior. They think the most appropriate thing to do is race up to the red light. So instead of profiting from the faster speeds out of the light, they instead cut you off and start the light cycle at a predictable 0mph. You haven't done anything except swap places with these jerks.
Please don't do this.
If there is a reliable way to move it behind me, I'd like to know!
What if every vehicle is separated by 2 seconds of stopping time, but all vehicles are moving at the exact same speed of 200 Miles per hour?
It would take one vehicle 0.005 hours to cover a mile (5,280 feet).
Assuming each car had a length of 10 feet, it would take 0.005/528 = 0.0000095 hours for a vehicle to cover it's own length at 200 mph.
2 seconds is the equivalent of 0.0006 hours. So each vehicle would take approximately 0.0006095 hours to cross any given point.
Providing a number of 1/0.0006095 = 1,640 cars per lane per hour according to my calculations.
I expected the number of cars per lane per hour to increase with speed, which is why I did the calculations, but apparently it does not!
If you could actually drive 200 mph on your way to or from work however, you would get there sooner than you typically do in traffic. It's an odd problem to think about.
Where we may see great improvements in road throughput is in driverless cars that greatly reduce that gap.
Cut that number in half from 2 to 1 seconds, and you would approximately double your throughput.
I found your article interesting in light of the popular traffic piece you mentioned, but ending it with jokey suggestions after a fairly serious analysis doesn't really make it clear if you're joking or not.
But hey, maybe @themodelplumber and I are the only two who thought you were serious.
This is so fundamentally mistaken as to make the rest of the analysis useless. Traffic waves account for the majority of highway traffic (excluding on and off ramps), and cause the flow rate for a road to be decimated. It should be obvious that avoiding rate decimation is (literally) an order of magnitude more effective than preventing people from merging in front of you.
Road signs commonly ask you to use both lanes up to the point of the bottleneck. That’s reasonable advice, but it’s not going to get anyone home faster.
No, but if your line is twice as long it is twice as likely to cause contention on the roads behind you. ie, if an exit road has a traffic line twice as long, it is probably causing traffic on the non-exiting highway. So, do everyone a favor and (a) don't tailgate (b) ignore people merging in front of you (c) don't drive in rush hour, and (d) ignore traffic advice from people who don't drive.
(http://tomvanderbilt.com/traffic/the-book/ has actual good advice)
If you simply kept reading:
>This is good because it is less likely to affect other traffic by spilling out onto onramps and surface roads. Also maybe there’s someone on the highway who’s planning to exit 3 miles before the bottleneck. If the backup is 2 miles instead of 4 miles, that person doesn’t have to wait in traffic.
Exit lines are particularly costly because adjacent lanes of traffic generally only sustain a 10MPH difference in speed. Once the right lane is stopped, a 4 lane highway has a maximum safe speed of 30MPH in the left hand lane. This reduces the flow capacity of the highway and may cause the left lane to lock up because left lane drivers get frustrated at slow speeds and are the more likely to tailgate and cause traffic waves.
His model also is only concerned with the self: "can I reach my goal any faster", and he reaches the mostly correct conclusion that he basically cannot (even though avoiding traffic waves by driving in the rightmost non-exit lane would help him significantly). He does not appear to value his contribution to the delay of the people behind him, which is where all the really interesting conclusions are found, including the reason why traffic wave busting is beneficial.
It's true that free will may make drivers tougher to predict than individual molecules. But molecules obey quantum mechanics and one could conceivibly construct probability distributions for how that particle might behave. In principle, probability distributions could also be constructed for the behavior of individual cars/drivers, so a statistical approximation for the behavior of the ensemble of drivers in a system is probably a reasonable aim.
cf. http://www.phschool.com/science/science_news/articles/ant_tr...
Currently I drive for about 15 miles on a major highway (during rush hour at least once) on most days of the week. I rarely need to use my brakes.
No, this is not how traffic works, the model is much more complex and you're missing very large dynamic effects.
The significance of that hump is that it represents a maximum carrying capacity for a road - an optimum speed. If you do the numbers I believe it's about 50mph. What I think is really cool is that when the road is completely at-capacity, traffic is stable above 50mph (as cars can just slow down and capacity increases) but collapses to a jam below below 50mph (because as the traffic slows down to absorb new cars, capacity falls still further).
This is way why, when the M4 motorway funnels down to only two lanes as you approach London, there is a 50mph speed limit - it literally allows the road to carry more vehicles per hour. I also suspect that it's another benefit (other than safety) of setting 50mph speed limits in contra-flows and during roadworks - it allows the road to carry more vehicles despite having fewer lanes.
When you merge, you're merging in front of somebody, so a rule like this, universally followed, is effectively a ban on merging. How's that going to work, exactly?
Travel time isn't the only consideration. Things like safety, fuel consumption, and stress levels are important too.
The difference is I'm using less gas and putting less wear on my clutch, brakes, etc. by leaving a big gap between myself and the cars in front of me.
Furthermore I find that my demeanor is much more calm and relaxed when I leave a big gap because I'm not tensing up to avoid rear ending someone every time I stop.
How will the commute times of those who sit there waiting to merge be improved? If traffic flow was heavy enough they would never merge.
If they didn't pack a sandwich they'd starve!
You can verify this yourself. Drive as smooth as possible. Smoothly accelerate and decelerate. Leave large gaps. Try to use both your accelerator and brakes as little as possible. Now observe aggressive drivers and memorize their car's make, model and license plate. Observe the amount of risk and effort they undertake to get ahead. Then observe them only getting about 5-10 car lengths for their trouble. Finally observe them stopped behind you two traffic lights down.
Laminar flow = turbulent flow, but laminar is so much better.
This is besides the fact that laminar flow reduces traffic waves, reducing the variance for all those behind you, leading to a reduced risk of death and injury for everyone in your lane. My driving style has probably saved a life, or two.
Don't hit the brakes before merging and when someone merges in front of you, you should have kept enough space so you do not need to hit the brakes. Really, I think traffic would move much smoother if drivers leave at minimum 2 car lengths of open space between the vehicles in front of them and only hit the brakes on the highway when it is absolutely necessary.
If all the cars are put to a halt because of quick and hard braking cars ahead of them, its going to cause a chain reaction that is way more time consuming to drivers behind you than the author's "2 seconds slower to destination" factor due to a merge in front of you.
As for late merging, evidence shows that it's more efficient in congested areas and by reducing the line, you help prevent spillover to other areas and importantly accidents due to conflicts. I can see one super suboptimal situation where a car completely stops to change lanes (into a stopped/slow one) due to bad flow, resulting in more than just a 2 second impact on one lane. MN signs say "use both lanes / take turns" and dynamically adjust based on traffic conditions. In LA, the "zipper merge" seems to be standard for most construction zones in traffic jams, with the only distinction being where you merge in the last 200 feet
http://www.dot.state.mn.us/trafficeng/workzone/doc/2004DLMS-... http://www.dot.state.mn.us/trafficeng/workzone/doc/When-late...
So, lets say you are stopped behind 30 cars and the first car is waiting for the red to turn green. Now, as soon as it turns green, it takes a second (or two) for the first car to start moving. After that second, second car adds another second before starting to move. Based on this, you won't move your car until 30 seconds have passed. Isn't this one of the big issue? If all of 50 cars instantly start driving once it hits green, wouldn't it reduce traffic jam greatly. Now, I do realize this is not feasible but if computers were controlling the car, 50th car can move instantly after green.
On a side note, I realize the bottleneck situation can't be solved easily BUT again, I think human reaction (response) time is a huge part of it in most of these scenarios. If computers were driving, I wonder if we can have 10 times the car we have today without traffic jams.
"If anyone tries to tell you that if only drivers left space in front of them and took turns merging, traffic would flow smoothly, and it’s only because of jerks that there are any traffic jams at all, just ask them what’s going to happen at the next merge. Where is that extra space going to come from? You cannot keep 2 seconds back from the car that has just merged in front of you without, um, slowing down. If the car in front of you is also slowing down for the same reason, you have to slow down even more. This is basically the definition of a traffic jam."
However, if you have two lanes, with one lane blocked, then wouldn't not allowing for another car to safely merge into your lane prevent them from merging? Then you have one lane moving quite fast, but the other lane would be going more slowly...
Like I say, there may be something I'm missing here, I'm happy to be enlightened!
I've thought for a long time that it would be fascinating to build a complex traffic simulator that could be used by people designing freeways, neighbors, shopping malls, etc to plan for traffic. Right now those designs are just based on best guesses (or terrible guesses) by architects and not simulations.
What do you mean by a ton of space?. What do you mean by 'not much'?"
The real question we should try to answer is "What is the optimum distance all cars should try to keep between them? And that can't be answered qualitatively, only quantitatively.
Things start out okay, but it quickly devolves into the back propagating wave.
I don't have a clue what the percentage to achieve critical mass is, but my wild-ass guess would be 20-50%.
Californians have this one covered.
The problem is that you don't know which theories other drivers have, so you don't know how they will react to different situations. If you don't know how other drivers will react, you need to drive conservatively -- which usually means slowing down.
Take a construction merge down to a single lane. It might be the case that it's best to use both lanes up to the merge, so that the traffic jam takes up less space. It might be the case that it's best to merge as soon as you figure out what's going on, to provide more time for the merge negotiation and reduce the risk of accidents at the merge point.
In reality, it doesn't matter either way. If I try to use both lanes, I don't know that I'll be allowed to merge at the lane closure. If I merge early, I don't know if someone is going to use the now-unoccupied lane to zoom up and cut someone off, making both lanes slower and more accident-prone. I can't do either one and confidently say that I've made the correct choice, because I don't know how other drivers will react. What I do is just pick one, and slow down when something unexpected happens.
This article also generalizes some things incorrectly (it seems based mainly on German data, presumably because they have better infrastructure for measuring such). For example, I live in the northeastern U.S. We are notoriously bad drivers up here, even among other east coasters. Here, a two-second following distance at 65MPH is almost unheard of -- actually, a two-second front-to-rear distance probably qualifies as a "large space", as some people here seem to think such a space can fit multiple vehicles. That's about 100ft or 30m, so I suppose it technically can, but it is not safe.
I can react to this either by leaving a very large space (5-6 seconds seems sufficiently large that people get impatient and leave before it fills up) or by leaving a small space (.75-1.25 seconds is the largest I can leave and have a good chance of nobody trying to use it). The former is much safer, so that's what I do.
The key is that, over a period of about two minutes, I need to maintain this following distance relative to the same vehicle. Usually this is fine: at most three cars tend to use that space at a time, and if anything they're more likely to tailgate the vehicle I'm following than to stay back near me. Occasionally I need to slow down in a situation where many vehicles fill that space, or someone moves in and immediately slows down. This is the exception, rather than the rule.
Yes, I know this behavior can cause traffic jams under certain conditions and with certain other drivers -- but so could the alternative, under other conditions. Given the choice between two bad options, I optimize for my personal safety.
