Traffic Experiments -- How to clear traffic jams
eskimo.com
eskimo.com
I'm telling you that, because as a frequent driver (well, today I drive a bike but still) in Paris, and kind of very observant, I clearly see that most people are not doing what these drivers do in this experiment. Most of the time, everybody will let a huge space between the car behind them in order to avoid changing the gears too frequently.
On the contrary, on automatic cars (I had one and drove another for 6 months in Canada), that's easier to go & stop & go & stop & go & stop, etc...
Not sure if it's related, but I think it is, in a small proportion.
edit: my english
I'm increasingly convinced that it's due to so many drivers optimizing for local minima, at the expense of not just everyone around them, but of themselves thirty seconds later.
It's also not uncommon for traffic to go from stopped, to fast enough to warrant 2nd gear, back to stopped.
Manual transmissions are definitely hell during rush hour... but doesn't seem to affect people contributing to the waves in my experience.
I base my commuting style on this guys articles. Drive slightly slower than everyone else and let large spaces grow in front of your car. It's a lot harder than it sounds (for me anyway) but when I get it right, it makes my drive much more enjoyable.
People that just HAVE to drive as fast as possible will go around you (you should never do this in the left lane) and everyone else will sort of get in line after you... it looks a bit like those nascar groups where all the cars go exactly the same speed.
Nobody else I've ridden with will do this (I've suggested it). Instead, they tailgate the slow car, curse like mad, and then almost cause a wreck when the try to pass the slow car in full-speed traffic as soon as they enter the interstate.
If you leave enough space you can easily get up to interstate speed and pass them quickly and effectively.
I don't feel like competing with them.
Personally, I'm not trying to fix traffic for everyone. I'm selfishly trying to make my own commute as pleasant as possible. By following the advice in this old article I've managed to greatly improve my own drive, and I find the amount of time I spend in the slow pockets of traffic greatly reduced.
You are not supposed to be driving slower. You are supposed to be driving in average speed with the traffic. You may have had to slow down in the first place to do this. If you are just starting out, a good rule of thumb is to just leave space between you and the vehicle in front of you; keep pace.
The key is to maintain enough space between you and that vehicle that you can
(1) allow people to freely pass through (they are going to do something crazy to do it anyway if they do not have the space)
(2) absorb traffic waves
It is likely you will not be able to do #2 consistently. But you can let off your gas and not hit the break. Hitting the break is an instantaneous warning signal to people behind you, causing something of a reflex for them to also hit the brake. You are trying to avoid the brake-light wave. Letting off easy generally does not cause as much reaction.
What if you end up in a traffic jam anyway? Leave space anyway. It does help.
Aren't more accidents are caused by people getting panicky as they try to cross lanes of traffic that are closed to them? They force their way in or speed up to get around a bunch of people?
It is all about leaving that space so they are comfortable. Everything begins to move faster. And you are more relaxed in your driving because you are not freaking out at what is going on in front of you, allowing you the freedom to react as necessary to all the other kinds of problems traffic can bring.
Intentionally driving slower over a long distance is a misapplication of the principles. As the article points out, it is all about the average speeds. Frankly, very rarely does anyone get "pissed", and all they do is pass around you. And then they end up hitting their brakes and shifting out quickly. Passing != bad thing; we are not trying to win a race here. I have never been honked at.
...As long as you're careful about doing this, of course. If the people behind you aren't paying enough attention to notice a slow decrease in speed (and can't see the reason you're slowing down), they'll be hitting the brakes hard to slow down when they're suddenly too close.
In hilly city driving (hi, SF), I will actually intentionally use my brakes to signal to the people behind me I'm trying to slow down, because there's often not enough space to notice when your line of site effectively stops at the next intersection's brief period of flat road. And yeah, this behavior was inspired by seeing someone rear-ended right behind me.
I also refuse to be pushed by people who ride my tail; I maintain my speed and ignore them (which is oodles better than slowing down to teach them a lesson, which actually does the other thing I was warning against here, causing a ripple in the traffic). It is my rebellious nature against their several ton weapon.
If you're interested in this there's a nice longer interview with Tom at Streetfilms http://www.streetfilms.org/tom-vanderbilt-talks-traffic or an hour long Google talk.
I agree though that it doesn't really work in all situations. Tom uses the example of two lanes merging into one for roadworks. Maybe some situations where it doesn't work are an example of poor road design by traffic engineers?
I've seen this [appear to] work in Seattle. While I was there, I tried it, and it appeared to work.
However, while I lived in Dallas, I was aware of this idea, and tried it there - and no way. People cut in, people tailgated - it completely doesn't work.
So I think it partially depends on the nature of the city's drivers. And there is something special about Seattle.
I still definitely change lanes more than most drivers around here - although I do my best not to cut anyone off, and I actually let drivers in here... something definitely not done often in Dallas.
It also helps that I went from a 90 minute commute (each way) to usually a 10-15 minute commute here (depending on where I've worked). Smaller towns do have some benefits...
In fact, a real solution to this problem that could be applied in the design of our current urban landscape would be a multi-pronged effort to spread out the commuter traffic. Alternating work and school hours could widen commuting hours and distribute load across all commuter infrastructure. Increased levels of telecommuting would also contribute to this. This would be a sort of supply-side fix to commuter congestion. Local or regional governments could create incentives to encourage these changes.
the capital investment needed is pretty fantastic
The problem with personal automobiles right now is that they are dangerous, slow, expensive, and have a huge carbon impact. We can find technical solutions to all those problems without restricting everyone's freedom of movement by forcing them into public transit.
Since I drive a car, every time I go out with my wife, I have to be careful how much alcohol I consume. If I had a train or bus to take, I could drink however much I wanted.
Since I drive a car, if I want to walk around town, I have to return to my car before being able to head home. If there was public transit, I could just go to the nearest station and connect from there.
Since I drive a car, I have to pay to park if I go downtown (and hunt for a parking spot).
Since I drive a car, I have to inconvenience a friend or pay for a taxi whenever I go to the airport.
Since we drive cars, my wife and I can't meet somewhere after work unless we we're willing to have two cars.
Since I drive a car, I have to pay for gas and maintenance, and there is no good alternative if my car breaks down. A bus line can just add another bus, or reduce the number of stops. The route doesn't just shut down.
But worse is the problem that once everyone slows past the 35MPH hump, traffic becomes unstable, and you get oscillations or standing waves which slow things far more than you might expect.
Rule of thumb (but I've never seen it stated anywhere) 35MPH=51FPS, 3 seconds between cars, gives 150 FEET BETWEEN CARS. Closing up gaps will wreck the max. flow pattern. During congestion, if you start trying to stop others from "cutting you off" or merging ahead, then you're the one causing the jam. (Or to be fair, 30MPH and 2sec gives 90ft spacing, perhaps the bare min.)
Another issue: in 1998 Helbing and Huberman discovered the existence of distinct 'phases' in simulated multi-lane traffic. When all lanes seem to lock together like a moving crystal, that's now called "Synchronous Flow," and gives maximum throughput. But it's on the edge of collapse, and "condensations" are triggered by anyone who tries outrunning neighbors by switching lanes, or who approaches too close and has to tap the brakes. http://www.nature.com/nature/journal/v396/n6713/abs/396738a0...
If you do this when traffic is not quite jammed, people are far more upset. It's best used when traffic is being forced to actually stop regularly. You will still get people to honk at you and whatnot, especially once a person or two passes you, but I've long since given up expecting most people to understand the things I do.
It could be related to driving a manual and being lazy, but it helps your concentration no end :)
On a side note, I also tend to play that "game" when stuck in slow home-from-holiday traffic over the mountains. Changing speeds all the time while driving manual is such a pain.
Imagine a [moving] wall, on an interstate, moving at 30MPH. No matter what is happening behind this wall, it is impossible to maintain an average speed faster than the wall. You can try any amount of tricks to smooth out traffic, but it will be impossible to ever move past this wall. As long as there is a steady stream of traffic, no car will ever do more than 30MPH until this moving wall gets out of the way.
So now let's, more realistically, replace the wall with a bunch of slow drives, and ask 2 important questions:
1. How to get out of this situation? -- We want these drivers to all SPEED UP! It's really as simple as this. Until these bottleneck drivers move out of the way, you can only smooth out traffic, but never increase the speed.
2. How to avoid this problem in the first place? -- In general, there will be some bottleneck. After too many cars are going through this bottleneck at once, there will be slowdown. Ideally, these bottlenecks should be identified and no more than the maximum amount of cars at a time should enter the bottleneck to decrease the speed of traffic.
Of course, that's easier said than done, but I think the important thing to take away from my ramblings is this:
The best way to get rid of a traffic jam is: if you are in the front of the pack and have a chance to accelerate, you should do so as quickly as possible. If everybody were to do this, average speed could then be increased.
In light traffic, some people go far faster than average, but nobody tries to stop them. When we arrive at heavy congestion, don't we suddenly decide to close up ranks to prevent aggressive drivers from passing, stop them from "cutting us off?" If everyone habitually blocks the speeders, then it means we've compressed the traffic pattern past the peak of maximum flow, and pushed it into the unstable realm of stop/go oscillations and standing waves or "ghost jams."
Want jams to vanish? Then do as the pro truckers do and just freaking back off. Happily encourage other cars to merge ahead. (They're not "cutting you off," there's no such thing as "cutting you off." They're just trying to merge into the adjacent lane!) If traffic momentarily slows way down, everyone just make sure to keep an open space that allows merging, and you'll find that it speeds right back up again.
On a related note, I wonder if "lane closed ahead" signs placed too far ahead actually make this problem worse, since many drivers will immediately merge out of the closing lane far ahead of time, causing a wall of traffic if the front of the line has to slow down for aggressive last-second merges.
So now when I'm in a jam, I just slow down instead of engaging the speedup, break pattern. Haven't looked behind me though to see if I had any effect on the traffic behind me.
To alleviate this issue "there are traffic lights at some freeway entrances to control the flow of vehicles onto the freeway when the traffic is heavy. When operating, the lights will change quickly, so that when the light is green only one vehicle in each lane will be able to enter the freeway." (taken from VicRoads website)
The lights basically cycle from red to green every 2 seconds. That's enough to regulate the flow onto the freeway and minmises jams on the entry ramp and at the merge point between the freeway and entry ramp.
In addition, most people would cut you of if you drove slower than the maximum speed.
I would be really interesting to see if this actually improved interstate bandwidth during rush hours. But even more interesting, I bet a good portion of drivers would get upset at the fact that there are huge, unused gaps. I wouldn't be surprised to hear from people who think it is grossly more inefficient than regular old traffic jams...
Please don't try this in the left lane.
He basically advocates estimating how fast traffic is really going, and going at that speed. Instead of reaching a bottleneck quickly, you should slow down appropriately in advance so that you never have to actually stop. Note that you (and the people behind you) still get through the bottleneck at the same speed, so there is no cost to you (or them), just less braking and accelerating.
For what it's worth, some freeway entrances near me (Melbourne, Australia) have traffic lights which rate-limit entry onto the freeway in peak hours. This is exactly the same as what this author is trying to do; by rate-limiting cars at entry, they're not actually slowing them down, since it increases average on-freeway speeds.
Here is the thing where it falls short though:
the guy at the front riding the wave really slow to "help lane locks" will also get merging traffic many many time right in front of him (people taking advantage of the free space), as a result, it won't help that lane but only make it worse if you're stuck behind such driver (or truck).
So if everyone stuck to their lanes, didn't change unless extremely necessary, and played the wave-canceling technique, it would work.
In other words, this will work when cars will be driven by computers hooked together via apis and maybe a traffic controller. I'm not signing for the beta.
The main cause of traffic wave is from someone stopping too abruptly, eg. if someone changes lane in tight traffic, he forces the other person to slow down too fast, which begins the wave.
If you allow more people to get in front of you in a smooth manner because you have given yourself a lot of distance, then there will be less 'cutting off' slow downs from the middle lane guys, which in turn causes less cutting offs in the right lane.
How much does it hurt over your entire commute to let even 100 cars in front of you? You'll be 500 meters later to your destination, what's that at 30kph...1 minute more? That's the worst case scenario. The normal case is you'll get there quicker because you've raised the average speed of the entire traffic wave.
Where I live there is terrible traffic... and I've contemplated causes and solutions many a mind-numbing commute. I realized we behave differently when we are behind the wheel... Very few people would behave or maneuver the same if it where lines of people instead of cars. That is why your best chance to merge is to make eye contact with the other driver - if they recognize you as another human not just another vehicle than they are much more likely to move over or make space.
When I drive (during rush hour) I suffer a lot to justify my actions. What I have settled on... is a simple rule: In any situation the person who is in the wrong is the one who has contributed to the impediment of the overall flow of traffic. This comes back to what zepolen says (and I agree with). If we could ever make the connection that what's good for my fellow (wo)man is good for me too... we would be so much better off in general.
Sadly, in the area I drive in, many drivers are constantly paying more attention to their phone than the road. Those drivers cause all of the traffic problems I see. They likely contribute to many of the accidents as well. They will end up leaving huge gaps in front of them at the expense of traffic behind them even when traffic ahead of them is moving smoothly and quickly.
The cost of letting cell phone drivers in front of you can be many minutes to your commute per each driver. Add a few minutes for each traffic light or merge lane that you will spend behind the inattentive drivers.
In a 5 mile commute, following the flow of inattentive drivers can add 45 minutes to my drive. Attentive driving and following the flow of other "aggressive" drivers can make it a 10 minute drive total.
So what I have actually found helps, in a real world scenario, not a fictional one where all drivers are equal, is trying to identify and cooperate with other "aggressive" drivers helps the group of aggressive drivers get through traffic efficiently and gives the cell-phone drivers plenty of time to concentrate on their conversations.
>Even if he's successful in removing the "wave", it's just by decreasing the average speed of traffic.
How would it decrease the average speed in any practical way? Secondly, it would dramatically reduce the energy consumption of the waves (accelerating and braking constantly) and wear and tear on vehicles. The net benefit of optimizing highway traffic -- in real environmental and economic benefits -- is significant.
>Please don't try this in the left lane.
The left lane has no meaning during congestion. There is no "passing" when the highway is clogged. And yes, this is actually the law in many places. One of the biggest causes of highway inefficiency are the self-important (but usually going nowhere) people who pretend that by driving aggressively, they should be allowed through the congestion.
(I've also seen markings to keep cars 10 metres apart on some roads).