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Traffic Hacks: How One Driver Can Vastly Improve Traffic (trafficwaves.org)
237 points by Mintz on Aug 25, 2009 | hide | past | web | favorite | 146 comments

I changed my driving patterns after first reading this remarkable essay some years ago. Now I follow what I affectionately call the "zen of driving", to wit: leave a huge gap in front of me, drive at a constant speed where possible [1], avoid using the brakes except in case of emergency, and so on.

On long driving trips through mixed traffic, I have made several observations, some obvious and some surprising:

* Driving in congestion is no longer stressful. It just isn't. (Hence the "zen".)

* Dramatically improved fuel economy.

* It's possible to drive through even wildly erratic traffic (swinging from 100 km/h to 20 km/h) without ever touching the brakes. It becomes a kind of game. Manual transmission helps.

* Some other drivers seem to figure out what I'm doing, and they fall into place behind me at a reasonable distance. I've had people follow me for hundreds of kilometres this way.

* Even though you'd assume leaving a huge gap in front is an invitation for other motorists to cut ahead, they rarely do - especially in congestion. If they do, I just let them race up to the front of the gap and then fall back by a single car length to restore the same gap.

I absolutely swear by this driving method. It's easier on the car, easier on the heart, and even serves to create a bubble of calm around you in an otherwise turbulent flow of traffic.


[1] Edit to qualify "drive at a constant speed". As I noted later, my speed ranges dramatically based on the congestion level - what remains more or less constant is the safe opening in front of me. Sorry for any confusion with my original choice of words.

That's not "zen" -- it's artificial regularity. Zen would be driving at what feels like a natural speed, only adjusting that when circumstances dictate, and "letting go" of your attachment to forward progress when something stands in your way. Instead, you're driving at an artificially limited speed to try to regularize your driving experience. You're tricking yourself into feeling less frustrated by consciously eliminating frustration triggers from the driving experience; a zen approach would involve simply choosing to feel less frustrated by "realizing" that the frustration triggers really don't matter.

> Even though you'd assume leaving a huge gap in front is an invitation for other motorists to cut ahead, they rarely do - especially in congestion.

That's heavily dependent on time and place. I've lived in many different regions, and done a lot of driving in those areas. I've noticed that the tendency to fill in gaps is heavily dependent on local driving culture and the specific demographics on the road at a particular time of day.

> I absolutely swear by this driving method. It's easier on the car, easier on the heart, and even serves to create a bubble of calm around you in an otherwise turbulent flow of traffic.

That may, to some extent, be an illusion. Some people are infuriated by other drivers they perceive as holding them up -- which often includes people who are "wasting" lane space by letting a gap of thirty car lengths lie unused in front of them. Personally, I only get annoyed with such people when they try to keep other people from filling that gap, because as far as I'm concerned a steady gap (given a steady general traffic speed) creates irregularities in grouping through which ambient traffic can accelerate itself, but people who maintain a huge gap then rush to block out people who want to move into it are increasing the danger of driving and doing nothing to help improve the flow of traffic.

>That's not "zen" -- it's artificial regularity.

Please see my edit in my original post to clarify what I meant to write. In fact my speed ranges up and down based on the level of congestion, whereas the safe buffer I maintain in front of me remains constant - and by safe I mean long enough that I don't have to use my brakes when traffic slows.

As for my use of "zen", don't read too much into it. It was just a tongue-in-cheek reference to the fact that I stopped trying to fight the flow of traffic and instead simply pass through it as peacefully as possible.

>That's heavily dependent on time and place.

My observations are limited to highways in Ontario, Quebec, New York State, Pennsylvania, and Massachusetts.

>I only get annoyed with such people when they try to keep other people from filling that gap

Hey, man, you're welcome to it. Blocking another driver from filling the gap would mean accelerating to close it, which kind of defeats the purpose of maintaining it.

I'm a Zen Master, I have the degree to prove it. Your use of the term has been approved by the ZCUZ (Zen Committee On The Use Of "Zen").

Children these days have no respect for Zen Masters.

Is that self-referential?

No, at least I certainly did not mean it to be. ;-)

The original comment, for those that don't get it yet, was a stab at apotheon's comment. It was an attempt to avoid the argument of "what is Zen" before it gets out of hand, as it's been known to do on other sites.

If you're curious, an example: http://zenhabits.net/2007/01/why-zen-habits/#comments

who is to say what zen is?

It is much easier to identify what it is not than what it is. One could even cheat by claiming that anything is "not zen".

I did exactly what you described on a recent 12 hour car trip. I'm never tailgating again.

The main benefit for me, and one you don't mention, is safety. Knowing I have actual time to react in an emergency instead of being stuck with brake hard and pray I think really calms my subconscious.

I'm constantly surprised by how few people have heard of the "3 second rule".

The rule is simple and works for any traveling speed: pick any arbitrary mark on the road, watch as the car in front of you passes it, and count 3 seconds. You want at the very minimum, 3 seconds to pass before you pass that same mark.

This not only has the advantages described by the OP (he's definitely following it, if not calling it by name), but one thing he didn't mention is that it can save your life.

Why do car "pile ups" exist? It's because someone was driving along just fine, when suddenly they come to a crashing hault (at 70+MPH), and all of the tailgators behind them are not physically capable of reacting to the situation in time. SMASH! You're fucked.

Many people don't realize that, even if you can somehow stop instantaneously, you're much less likely to be hit from behind if you have time to gradually decelerate.

"only a fool breaks the 3 second rule" (takes roughly 3s to say)

Mr. T's Guide to Safe Driving

Wouldn't that be "I pity the fool who breaks the two second rule"?

Except that this only gives you a linear amount of space with respect to your speed. You need space that goes as the square of the speed.

Depends. For cancelling your reacting time you only need linear speed. And if the vehicle in front of you has the some breaking deceleration as you can achieve, that's fine.

I use this rule too with a slight modification. I always try to keep an older vehicle in front of me and a newer behind me, without overtaking anyone if possible, in order to take advantage of the different braking distances of each.

Of course, if it's wet weather, you'll want to increase that - say to a 4 second rule.

I was taught to leave 1 car length per 10 mph of speed, which probably has about the same effect. Either way, I've been driving for a decade and haven't hit anyone yet.

I remember being taught more like 7 seconds, but that might have been for freeway driving.

The point of counting seconds instead of distance is that it works at any speed. People tend to keep the longest (time) distance at suburban speeds.

7 seconds at highway speeds can be over 200 meters.

I'm all for safety, but that is excessive.

If you break faster than most other cars will often get rear ended, it's not just cushion for you but also the car behind you. Try to break from 70 on an empty road after 2 second reaction time and see how long it takes and how far your car travels, and then consider what would happen if someone was tailgating you at the time.

PS: Thinking you have a 2+ second reaction time helps to cover when you are not directly looking at the car ahead of you. The less of that cushion you have the more you need to focus on the car in front of you.

There are a lot of driver douches which will always overtake whatever is overtakeable, driving like this makes you an easy 'target' and that gets me all worked up.

edit: spelling

Except it doesn't. Like I said, I rarely experience drivers cutting in front of me.

In what part of the US do you live? Having just completed a cross-country move, I can assure you that driving behaviors wildly vary from coast to coast.

Yeah, come to Massachusetts and I'm sure you'll have an entirely different experience.

This varies dramatically depending on what highway you're on.

I've driven like the article suggests on Rt. 128 and it totally works. My lane ended up moving smoothly (albeit at a reduced speed; I still can't go any faster than the average speed of the cars in front of me), and nobody cut in front of me.

However, drivers on Rt. 2 are routinely crazy. There've been times I've been going about 70 in a 45 zone, with a guy on my tail, then he'll pop out from behind me, pass me at about 90 mph, cut right in front, and then tailgate the person in front of me until he does the same stunt. Luckily traffic on Rt. 2 is light enough that this doesn't cause many jams, but it does cause its fair share of accidents.

Then there's the Rt. 2/3/16 intersection by Alewife, where it is customary for about 5-10 cars to run the red light before somebody finally stops.

I generally follow the stated driving pattern on 95, and it works just fine.

My observations are limited to highways in Ontario, Quebec, New York State, Pennsylvania, and Massachusetts.

I've seen some pretty crazy driving in Ontario on the 401 and the QEW. Especially driving in downtown Toronto on the Gardiner. I used to commute Toronto -> Niagara Falls for work, and I saw people do some pretty stupid stuff (people driving at freeway speeds @ 5am, pitch black with so much snow on the freeway that you can't see the pavement at all, and multiple spin-outs along the way).

The worst drivers I've seen in my life have all been on 400 series highways.

I figure if my method can work here, it can work anywhere. :)

Where do you drive?

I tend to leave about twice the gap of other vehicles on the motorway, still strictly not the full stopping distance (but having been a motorcyclist I feel I read ahead well). I always find that people invade my stopping/slowing space; then one drops back and another car is in there.

I'm in the UK.

I accidentally get a similar effect when I try to drive a patch of road with the car in neutral. It's a very non-intuitive experience: from the engine sound I'd think I'm slowing down considerably, but from looking at the numbers I stay at pretty much the same speed for a looong time.

When I do this before stoplights I sometimes catch a green light with road to spare, and I'm able to avoid stopping at all. This helps me somewhat, but as a side effect it helps the traffic behind me a lot more.

I'll try to do this more often. Keeping in neutral is easier then trying to compute an optimum speed, and it'll help a lot with the consumption too.

IANAM (I am not a mechanic) but I've heard that it's bad for an automatic transmission to coast in neutral. Apparently the transmission isn't being lubricated in neutral, there's a risk of overheating, and it can be damaging to shift back into drive at high speeds.

In any case, you're not really saving any gas over coasting in drive or, alternately, setting the cruise control.

I don't know about automatic transmission. As for the fuel economy, I find it's easier to slow this way without really trying. Just put in in neutral when you see a red light. Of course it's only for before intersections/blockages, not on the highway.

I've been doing the same thing for some time now as well. As well as what you have observed I have observed that you really can actually hack the traffic to reduce congestion. I've seen a gap that I brought to a merge point allow 8-9 cars to move and several hundred meters of stationary traffic was able to pick up speed enough to merge, I could see both lanes continue to flow in my review mirror.

Instead of competing to get ahead the game has changed to strategising to keep the traffic moving. It's beautiful and fun and transforms the whole driving experience, very zen.

"I could see both lanes continue to flow in my review mirror."

Heh, you didn't happen to learn to drive in, say, Massachusetts did you? It's called the "rear view mirror", but I've found that due to the accent, many people here in Boston have always thought it was the "review mirror".

I started rolling like that when I got the Prius. You get some nice positive visual feedback when your instantaneous mileage maxes out.

Absolutely. I've tried to impart this to others, but the inescapable response is "someone will jump into the gap." If they would just try it..

I picked it up from truckers, who uniformly take this strategy.

There seems to be a difference in trucker culture between the US and UK - truckers in the UK don't seem to practise this technique.

While there are some courteous and sensible UK truckers, most of them seem to be driving right up against their speed limiters, and will tailgate then overtake anyone in front who dares travel 1mph slower than them - even if this involves attempting to overtake while going uphill, causing a wall of congestion on an otherwise free-flowing motorway.

Not only does a manual transmission help, but it kind of pushes everyone into that kind of driving. Maybe it's just because you don't need brakes as much. When I drive an auto (usually rental), I find I'm a lot more aggressive.

I also fond that places with a higher percentage of auto drivers are heavier on the heavy traffic scooch-and-brake.

In Germany manual transmissions are the norm. I heard people drive more aggressively than in the US. Might be a cultural thing, though.

It's not a straight conversion to aggression. Germans, I believe, drive fast. Maybe aggressively too. But, if you put them in an auto, they also pick up the behaviour of building speed fast for 1-2 seconds then braking hard. It happens a lot in dense, halting traffic. It's not the only way of being aggressive, but it's another way

People don't do that in a manual because it's not fun.

*In Italy people drive mostly manuals. They also drive like suicidal grandmas in fast forward.

All good points, but one that is even more important while careening down a concrete road at 60mph: safety. By traveling at a slower speed and not changing lanes you are drastically reducing the odds of getting into an accident.

This is almost exactly my approach. For a while, I was working on a web page to share the heuristic I'd worked out for it, but I ultimately figured it wasn't worth the time. Since it's relevant to this thread, here's my heuristic:

1. Are you driving faster than the speed limit? Coast. If not … 2. Can you see more brake lights (that is, cars with brake lights on) ahead of you than the number of lanes traveling in your direction? Coast. If there are more lanes than cars with brake lights … 3. Is the buffer between your car and the car in front of you getting smaller / staying the same? Coast. If the distance is getting larger, you can accelerate.

So, essentially, the only time you get to accelerate is when you're below the speed limit, there aren't many cars braking in front of you (in any lane), and the gap in front of you is getting larger.

And here (below this) was the copy I'd worked up for the page. I was calling the approach "coasty," and was applying some game design theory to it, so if there are any "game" references in the copy below, that's what they're referencing.


The goal of Coasty is to consume less gas, to drive more safely, to get to your destination in about the same amount of time as you would otherwise, and to have more fun while driving.

Consume Less Gas:

Almost every time you brake, you’re wasting gas. You had to use gas to accelerate your vehicle, and you’re now intentionally slowing the car down. You’ll then need to accelerate again, to get back up to speed. You're doing twice the work, for the same amount of output. By braking less often, you end up accelerating less often, getting more miles-per-gallon and saving money (both in gasoline and engine wear). (Obviously, if you’re braking because of a stoplight / stop sign, this doesn’t apply.)

Drive More Safely:

When you're driving aggressively, driving closely to the car in front of you, and focusing on getting where you’re going as quickly as possible, the more likely you are to get in an accident. The amount of space and time you have to make a decision (and execute it) is determined by the amount of space your car has in front of you, and the speed at which you’re traveling. It’s counter-intuitive, but by focusing on braking-and-accelerating as little as possible (and by coasting as much as possible), you end up with a larger buffer in front of you, and you generally enter that buffer at a slower speed.

Get To Your Destination In About The Same Amount of Time:

It’s not fun to be late. And — let’s be honest — you probably aren’t going to stick with a new approach to driving if it compromises your ability to get somewhere on time. But with this approach, you’re reaching each “micro destination” (that spot further down the highway, that exit ramp, that streetlight) only a few seconds behind where you’d be otherwise. In some cases, you'll get there even faster, as you might end up approaching a stoplight while coasting, as it turns green, rather than approaching it, stopping, waiting, and then accelerating again from a stop, while the guy in the lane next to you cruises through at 10 miles an hour.

Have More Fun While Driving:

This approach actually makes driving fun, as the goal shifts away from “getting where I’m going as fast as I can and who do these jerks think they are, getting in my way?!?!” to one of a game mindset, where you’re trying to follow the rules, seeing how far you can go without braking, and seeing how much your fellow drivers have to speed up and slow down while you’re coasting along.

As a side benefit, creating a larger buffer and then eating it up enables the cars behind you to have a smoother trip at a more constant speed, where they aren’t having to brake as much, either, and dissolves the slow-down-then-speed-up-then-slow-down-again rubber-band traffic cycle.

You must not drive much in places where the effective speed limit is higher than the posted speed limit -- which, in my experience, is almost everywhere. If you drive the speed limit or less in other than heavy, slower than usual traffic, you get tailgated and cut off regularly, and actually contribute to traffic snarls by introducing additional variances in the flow of traffic.

Dad called it "cruising."

The government calls it "speed limit."

This man is a saint. For years I've wished more people understood these principles. Instead, I get drivers who are angry at me for leaving a big space in front of my car. If only I pulled up right behind the car in front of me, they'd be 60 feet closer to their destination!!

I wish more people would check this site out. Traffic is a real problem that wastes billions of taxpayer dollars and hours on the road every year.

Another idea to make the roads better: lane-specific minimum speeds. Think about it. It would actually solve a ton of common traffic problems.

Another problem is drivers who insist on driving in the left lane at all times and refuse to move over. IIRC, the left lane used to be referred to as the 'passing' lane...

There are even laws on the books specifying the left lane as the "passing lane". There seems to be a recent trend in making these more strict, so I wonder what effect they're having. This guy seems to have an up-to-date catalogue (green indicates more strict):


In the UK it still is, and passing on the left is illegal. I like that system more that all lanes equal.

Took me a moment to understand because I forgot that in the UK the sides are exchanged. Left = Right and Right = Left in traffic. :-)

It is the same in Germany. I always assumed it was that way everywhere.

So if there is a slow car there, what do you do? Does everyone wait behind them until they turn/exit or decide to switch lanes?

If there's a slow car in the outside lane, and they're not making any attempt to overtake anything, you generally flash them until they move over. They are, after all, breaking the law.

What if a car is in the passing lane doing the speed limit? Asking them to move out of the lane so another driver could pass by speeding, breaking the law, doesn't make much sense either.

It's a grey area, although usually accepted that 90% of drivers drive faster than the speed limit anyway.

If it's a 70 limit, and someone is in the passing lane doing 70, you'd still flash them.

If he's driving at the same rate as the cars in the inner lane, he shouldn't be in the passing lane.

Speed limit on an Autobahn?

(OK, there are speed limits on most patches of the Autobahn. But there are some without.)

Yes. It's amazing to watch if you're used to driving in the US. You'll get an unbelievable amount of grief if you allow yourself to be approached from behind in the inside lane. Even driving in the center lane, you are expected to move outside if there is room to do so. Try driving there long-term and you'll get fast drivers cutting you off from the passing lane just to teach you a lesson.

And no, nobody passes on the outside. Even if you're about to exit and the rest of the lanes are moving slowly, you'll still slow down considerably and look a bit sheepish as you drift past the main highway traffic.

Occasionally idiots pass on the outside.

In Indiana and Michigan, left is a passing lane.

One problem here is that people driving the maximum lawful speed are still driving too slow for the prevailing speed of traffic.

So the difference is between "left is a passing lane" and "no passing on the right". In other words, it could be the slow car in the left lane that is breaking the law because it is not passing, just staying there, or it is the other cars that pass on the right that are breaking the law. I am sure the police would rather have both -- ticket those hanging out in the left lane and those passing on the right. Win-win for state/local budget!

There is no law against "passing on the right", at least not if this means "passing someone in a left lane while you're in a legitimate lane to the right of that vehicle".

For example, in the state of NY: Before you pass on the right on multilane roads such as expressways, make sure you check your mirrors, use the proper signals for lane change, and look over your right shoulder for other vehicles. After passing, be sure to check over your left shoulder, and to signal, before returning to the left lane. http://www.nydmv.state.ny.us/dmanual/chapter06-manual.htm

The thing that drives me nuts the most is slow people who stay in the left lane in the passing lanes that are sometimes put in on 2 lane highways (ie, 2 lanes going in the same direction for a time). Some states (Minnesota for sure) simply make a solid line to shunt drivers over to the right lane and it makes a huge difference, but around here (Wisconsin) they don't do that and inevitably I'll end up stuck driving 45 on a behind an old camper on a 2 lane highway because they refuse to keep right.

IIRC from drivers' ed, it's illegal to do this unless you're passing or preparing for a left turn.

perhaps if this was enforced more routinely it would help with the principles discuss in the article.

I suspect that (some) drivers instinctively measure their speed relative to other cars rather than the background. If they're not overtaking other cars, they feel like they're not moving.

Yes, this is exactly right and is confirmed by nearly all of the research going on with regard to traffic and driving.

These ideas work, but only if you can get everyone else to play along, knowingly or unknowingly.

In Chicago at rush hour, if you leave more than a car's worth of space ahead or behind you, it will be filled instantly.

People think this about 128 in Massachusetts, too, but generally what I observe is that people leave my "empty space" about as often as they enter it. I leave a big empty space for safety reasons, and also because I actually understand how inefficient constantly accelerating and braking is. I'm usually able to maintain it without too much trouble.

Whether or not it actually helps traffic, I couldn't say.

This seems like it'd create a danger if you're actually adhering to your goal of maintaining the "empty space": as soon as someone pulls into that space in front of you, you no longer have an empty space, and the only way to restore it is by slowing down to allow space to open up again. Which, as repetitively and suddenly as you'd have to do it, would pose a hazard to traffic behind you.

The typical solution to that situation is more like "Wait 30 seconds. The person who just pulled in front of you catches up to the car in front of him, and moves out of the lane to get around."

In the rare situations where this doesn't happen, I usually have a longer space than I actually need, so I just eat the difference.

Is that an assumption or something you've tried?

If it's the former, he addresses that concern on his site.

In my experience these ideas work even if you're the only one following them.

It's from 25 years of experience. Noodle from Atlanta has a similar experience in the comments below.

Try it and report back to us.

Minimum speeds aren't a good idea because of adverse weather conditions.

Some Japanese scientists did a study to show how traffic jams can appear of of nowhere. They told 22 drivers to drive in a circular path at 30 km/h. A traffic jam appeared, and moved backward. The video is here: http://www.youtube.com/watch?v=Suugn-p5C1M

Jams move backward, a well known phenomenon. That they appear "out of nowhere" is more interesting.

It is interesting but not inexplicable. For instance take a scenario where one driver sloooowly passes another on a two lane road. This effectively clotheslines the road and causes anyone who would drive faster yet to pile up behind the two cars--maybe even apply their brakes.

Again, consider a sudden lane change that cuts off someone who's already in the lane being entered.

Yet again, consider that most on-ramps are essentially a reduction of available lanes.

Any time one car slows down for any reason, inertia kicks in--they do not immediately return to speed.

In this case, small variations in speed mean that some drivers eventually catch up to others. Then they slow down a bit which reduces the space behind them. The problem is that the road is nearing peak capacity and has little tolerance for deviations.

It's not 'out of nowhere.' It's because we're humans. We're paranoid and reactionary. You wouldn't see that with robots.

If I say I made a cake 'from scratch' (idiom: 'from nothing'), do you quibble that flour and eggs were indeed used, and that they are clearly not 'nothing'?

Mentioning how you made a cake from scratch and linking to a video of seemingly scientific research claiming an event to happen out of nowhere and for no apparent reason are two completely different things, due to the two completely different contexts.

I think his point was that we all understand that "out of nowhere" doesn't mean "magically", at some level it has to be the drivers' fault.

The video doesn't even say "out of nowhere", it says "for no apparent reason".

Cynical much? How about it's because we have bounded cognitive abilities, limited perceptive accuracy and slow reaction times?

You're forgetting the natural caution and fearfulness that protect us from depending too much on our limited abilities when safety is at stake.

That too.

You can certainly program robots to do that. The question is whether you can program them not to without losing something important (robustness against unexpected conditions or malicious robots, for example).

Emergent network phenomenon is emergent.

Ever since I can remember, I've always thought this was obvious, a product of random slowdown being amplified by reaction time delay. Motorway pileups are well known to be exacerbated by close driving, because each subsequent driver has to brake harder and harder to stop. Jams are just a less dramatic form of the same thing.

"WHY must a bottleneck develop at a merge zone? Well, obviously because there's too many cars on one road. And because everyone must take turns slowly merging together. WRONG! Wrong wrong wrong. Even during extremely low-traffic conditions, everyone still takes turns, yet everyone merges as a high speed flow,like a zipper. A bottleneck never appears."

New York city drivers are really excellent at the zipper merge thing. While living there, I got really used to not having to slow down much at merge points. Everyone just drove at a decent speed using all available lanes then smoothly merged at the point where the lane was closed.

Moving back to Pennsylvania, people start queuing up in one lane a mile before the merge point, and traffic grinds to a stand still. This is insane. Usually, though, if you do the sane thing and use the other lane up to the merge point, you can get in without trouble.

Maybe I was one of the early mergers before I lived in New York, and have just blocked it out of my memory. Now, though, seeing it happen really grates on my nerves. One of many reasons I'm glad I hardly ever drive anymore. :)

I've been driving like this ever since I heard a show on Wisconsin Public Radio where they interviewed a traffic researcher. One thing that is not true, however, is that "cheaters" are always wrong.

For instance, there is significant research that suggests in a 2 lane situation where both lanes must merge into one single lane (road work ahead, for example), it makes more sense for both lanes to proceed uniformly toward the point where they must merge. Most people would assume this would cause a deadlock at the point where the merge occurs, but it doesn't. When both lanes are allowed to proceed without switching lanes towards the point where they both must merge, they will achieve far better results than if they were to organize into a single lane prior to that point.

This makes people /really/ angry. Once, when there was approximately 2 miles notice for road work, I stuck with the right lane and did not merge into the left lane like everyone else. I actually had a large pickup truck attempt to cut me off from proceeding in an EMPTY lane.

Of course, this only holds when there is an inevitable traffic jam. When it comes to /avoiding/ traffic jams, you are better off maintaining distance to allow other drivers to merge.

It saves a lot of gas too. I've always tried to get through stop and go traffic smoothly without using the brake, but I always did it for my own gas consumption. I never had this macro look at it.

Especially if you drive a standard transmission. Staying off the brake makes a huge difference, and makes for less clutching as well. For bonus points, you can put the car in neutral while coasting, although some don't think that's safe.

On modern cars with manual transmission, the motor is powered with some gas when it is not engaged. However when you leave it engaged an just don't push the pedal, no gas is needed. (Although the motor brakes somewhat. I don't know which effect is stronger.)

Doesn't this imply that cities could alleviate traffic pathologies by hiring people to drive carefully down the highway?

This was the focus of a short video a group of college students made a few years ago, "A Meditation On the Speed Limit."


Is that the video in Atlanta where they drive side by side around I-285 at the speed limit of 55 mph? It's an interesting social experiment, but I'm surprised none of them were driven off the road. Traffic on the left on 285 generally moves at 70 - 80 mph here.

He suggests on one of the later pages that cities should have state troopers drive in a constant-speed band across the lanes. (He also points out that group of citizens doing this independently in Toronto was arrested for it.)

i think its interesting that i used to drive like this site describes for the exact reasons it talks about. and now i don't/can't. the difference? i moved to atlanta.

rush hour drivers here operate under a greedy algorithm. they see an opening that will allow them to speed up or gain extra distance immediately, and they'll take it, for no other reason than to be going faster right now, to be farther down the road right now.

and that includes eating up my buffer zone, forcing me to break/stop, killing my flow optimization.

That (in addition to the fact that everyone lives in the suburbs) perhaps provides some of the explanation for why Atlanta rush hour traffic seems to be some of the worst in the country, despite having more lanes and a smaller population than cities that have better traffic.

I have had to commute on two of the top ten worst rush hour stretches of highway in the country (and they're within a few miles of each other in southern California, on the 91 and I-10). Noodle is exactly correct that such driving "cultures" do exist, and they make this consciously regularizing driving style worse than useless.

I'm a fast driver, and one thing I will never understand are those who will do anything and everything to box in a fast driver, or to prevent them from cutting into a lane and taking off. I see fast drivers as excited molecules, looking to escape. What often happens when a fast driver is being blocked is they'll switch lanes back and forth, looking for their escape, creating this wave of hesitation, causing this big low speed anchor to form.

Someone driving fast won't suddenly stop the speeding after being blocked. Just let them go!

I am a fast driver, but in traffic I switch to wave abatement. It seems only logical to help the system when there is no way to personally benefit. (Except that moving to the right-most non-merging lane will help you avoid waves and move faster.) My prioritized rules of the road are:

  1) go whatever speed you like
  2) empty lane to your right? move right
  3) no car in front of you and a car behind you? move right as soon as possible
  4) slower car in front? move left if you can
These simple rules cover most situations in a way that benefits everyone involved. They do not cover some minority cases: aggressive tailgaters and high relative lane speeds (I leave a buffer lane if > 10 mph and no cars behind me).

I read this a while ago and I try to do it whenever I find myself in traffic. If nothing else, it is immensely less frustrating to drive a constant 15mph than to drive 30mph half the time and be at a complete stop half the time.

While I have not conducted any format experiments in the efficacy of the advocated driving method, I can report that it's far more relaxing than tailgating. Give it a try!

When I accidentally end up on Rt 128 at rush hour, I do this.

(I note that I was on a mailing list with a bunch of relatively smart people once, and I mentioned what I did - and even among the smart folks there was a lot of outrage because I was driving "wrong" or "stupidly".

That reaction contributed to me leaving the list shortly thereafter. )

How happy I am to live (and work) at the portion of Rt 128 which is separate from I-95!

But every time I go down to Boston, or far away to other urban areas, I can never keep the distance that I want because someone would certainly cut in. So I increase the distance again, to avoid tailgating, then another guy gets in between us, etc, etc. And so we have a peloton of cars moving at 65+ mph a few meters away from each other. Not too pretty.

Nice use of "peloton".

Unfortunately (and unintuitively), a person's intelligence doesn't directly translate to the type of driver they are. That's a perfect example. Shame.

Interesting, my instinct has always been to try to "punish" the cheaters by preventing them from merging in, thinking that this would discourage this behavior. But I can't really stop this, and the article provides a good explanation for why you might as well just let people merge in front of you.

The problem is that allowing merges incentivizes zooming ahead in the merge lane, which should result in there still being drivers who can't merge, creating the jam. I don't have a good solution for this.

To an extent I think you're right and some people will do it regardless. On the other hand, smoothly flowing traffic creates an incentive to not zoom ahead in the merge lane. There's less of a feeling of a need to cut ahead and people don't seem to do it as much when there isn't already a jam. (That is, the jam provides an incentive to cut in front of everyone)

And if people were to implement this strategy, the provided space gives an incentive for those zooming ahead to merge a little sooner rather than risk waiting half a minute for someone to let them in right at the exit. It's been my experience that most of the "cheaters" will merge a little sooner if there's space rather than zoom up right to the end. They'll still be passing you, which is IMO aggravating, but at least things will move a little sooner.

I used to as well, until one of the cheaters got out of his car and yelled at me at the next traffic light for "cutting him off". I decided that this potential outcome wasn't really worth it, especially since they always find a way in anyway. Another upshot is I also don't have to focus as hard on not rear-ending the person in front of me.

I've actually done this on my way to/from work, and it makes a legitimate improvement in my commute.

For anyone else fascinated by traffic patterns and driver behavior, I recommend reading Traffic: Why We Drive The Way we Do and What It Says about Us

The author goes into fascinating detail about driver psychology and discusses similar ideas like those mentioned in the essay.

Link to book: http://www.amazon.com/Traffic-Drive-What-Says-About/dp/03072...

How One Driver Can Vastly Improve Traffic

Yes, but that one driver is never the guy in front of you.

I respect this guy's patience, but the primary reason that one car can make such a big difference in this case is because 520 (one of the most important commuter roads in the Seattle area) is just two lanes in each direction. One car on a three lane road will just be passed.

The counter-point to this, in my opinion, is that at some point psychology comes in to play and you have people starting to get aggressive and angry because of a few people forming a "rolling-road-block". It's not rational but it definitely happens.

I would support 3PM-7PM dynamic speed limits on 520W toward the bridge. If the speed was brought from 60 (just past 405) to 30 as you approach the bridge it could probably keep things moving smoothly through the traffic burst.

I read this site a few years back and I've done a bit experimenting. I'm convinced that leaving space in front and avoiding sudden changes on speed are really helpful. Some times I have even seen traffic jams disapear if I leave a lot of space in front.

This essay should appear as a Public Service Broadcast through all media outlets.

My biggest complaint about this is that it's going to give many people who don't actually help traffic, and just drive slowly, feel self-righteous about their driving habits. Yes, in some circumstances this driving style can help traffic; no, it doesn't mean that driving 15MPH slower than ambient traffic is justified "for the greater good", especially if you're the type who jealously guards the thirty car lengths in front of you, accelerating to keep people from changing lanes in front of you.

Nice, patient guy but there's a better way yet if you can afford to gamble with your time a bit (don't try this if you can't afford to lose a little time).

When confronted with a single backed up lane, use the uncontended lanes to zip to the front of the wave and merge in _at speed_. Maintaining speed is important. If you don't find an opening, you'll have to abort and find another route to your destination.

The up-side is that this almost always pays off and you waste little time slowed by traffic or slowing others. The reason is because many people who queue up resign to the monotony and pull out their phone or their air drums, etc. They pay enough attention to brake consistently but not enough to accelerate as soon as is possible.

The vast majority of the time, you can slip in front of one of these 'sleepers' before they notice the opening or have fully accelerated. Because of inertia, they will go through an acceleration period where you pull away from them leaving them a very sufficient gap.

Another way to look at this is using the available real-estate to ascertain a proper zipper-merge. If done right, you wait less and no one gets stuck behind you. This is especially useful if you commute five days a week--the payoffs over time are well worth the occasional crap out.

I take issue with your theories. The "payoffs" you allude to do not exist. Your "zipper-merge" costs you gas money, and if you took the time to watch the video, you'd realize that you are considered a "cheater". Cheaters feel better about having gotten in front, but what they don't realize is that the "sleeper" is providing a way for cars to merge, thus alleviating the jam in the first place. All you're doing is typical busy-body traffic maneuvers that soothe your rattled frame, but do nothing to actually get you to your final destination any faster. The difference between maintaining adequate distance and doing your patented "zipper-merge" have been proven to shave at the most, a minute and a half off of your commute. Even if you do this five days a week, you're saving roughly 8 minutes. If you think that's worth it, then you should also be aware that the vast majority of accidents occur while changing lanes.

Actually, this study (http://ops.fhwa.dot.gov/wz/workshops/accessible/McCoy.htm) lends credence to the claim. Late merges have better throughput than early merges when encouraged by traffic signs and uniformly adopted.

The study does not directly address the effect of "cheating" late merges which can create waves, but did note that traffic signs which strongly encouraged early merging by everyone increased overall transit time through construction. That suggests that the default case is better.

That makes a little sense to me: a single lane can bear less traffic, so extending the amount of distance everyone has to spend in a single lane might result in higher latency overall, if not necessarily lower throughput.

"Constant velocity" applies to lane changes, as well. I hate when people are going 70mph and slow down to the 55mph of the car in front of them, THEN change lanes. No, change lanes as you're coming up on them so that you maintain a constant velocity.

Related to this is the need to "stay right". Especially in CA, some of my fastest travel happens in the far right lanes because people think of lanes as a "speed" rather than a "function", and so the right lanes are empty while the left lanes are crowded and slow.

The number one lane is not the "fast" lane, it's a "passing" lane. Guess what? The number two lane is a passing lane, too. If you're not passing anyone, you should be on the far right side of the road.

This is a representation of classic game theory. If all participants cooperate to drive as described, the traffic clears. If nobody else helps to open up space, however, you will personally arrive at your destination slower by driving passively, even though many others behind you will benefit. And since this type of driving requires some degree of altruism, you can pretty much rule it out as a realistic outcome without introducing another constraint (eg. as mentioned in the article, state troopers merging into traffic and forming a rolling barricade).

However, if everyone carried 10-15 extra car-lengths ahead of them, the total capacity of the road would be greatly diminished; you would just be moving the jam to the on-ramp.

The peak performance of the system is actually a mix of altruism and selfishness.

That's a fallacy, addressed by the site -- in short, the benefit gained by minimizing jams more than offsets the increased space between vehicles.

I think you may have misunderstood my point, which is that peak performance is attained when a few drivers drive altruistically (as the author does) and the rest drive "normally". If all drivers choose the same behavior (all altruistic or all normal), then the system doesn't work as well. This is interesting from a game-theoretic standpoint.

The author says much the same thing on his FAQ page:

If EVERY driver was to constantly maintain a HUGE space regardless of speed, then it would probably cause problems. The merge-zones might stop jamming, but the capacity of major highways would be reduced. On-ramps would become choked as traffic backed up into them, and there would be slowdowns extending far out into the countryside.

It is, of course, a purely theoretical problem, since there is no shortage of non-altruistic drivers.

Travis, the research out there on traffic jams suggests that even by driving completely altruistically, you add mere minutes to your commute. You also avoid changing lanes and driving at faster speeds, both of which are linked with an increase in accidents.

I completely agree with the moving wave! I have pondered this very same pattern myself. I'm excited to see it documented and shared on the web.

Taking this "zen" driving a step further and imagining an ideal world of cars that never break down on the highway and where the process of merging onto and exiting from a highway could be scientifically mastered such that the speed of the nearby cars is at most nominally affected, it is not inconceivable that cars could travel at speeds far beyond what is considered safe today.

Makes me think of Drum-Buffer- Rope from Theory of Constraints. Maybe we need a pull system for roads. There are a few onramps on criminally undersized (due to nimby nutsos) highways in my area where a traffic light limits flow onto the road at busy times- smart. Then the same people put in stoplights at the ends of the offramps, backing traffic up onto the highway.

BTW, sorry if this sounds off-topic, do you know any good books/articles on Traffic? I'm very much fascinated by this too. Thanks.

Not even close to off-topic. Traffic problems (and queuing theory) have a long history in CS, and the related problems have applications all over the place.

Can you recommend any good books related to Traffic issues for a beginner and intermediate? Thanks.

a coworker of mine recommends Traffic, on this topic, by Tom Vanderbilt.

My friend and I have designed, in our 6th semesters, a 8085 microprocessor based, congestion-aware traffic control for crossroads.

The system uses switches on the roads ( replaced using RFID or other sensors placed on the ground or at the sides of the roads ), that detect the load on each path and route traffic accordingly.

Not much, but it worked like a charm !!

While I find letting the 'cheaters' in grates too hard on my soul I alway try to practice driving at the average speed and avoiding using the brake. If for no other reason than to avoid wear on the car (in the UK most cars are still manual and so each start is a tiny bit more wear on the clutch as well as the brakes).

Kinda related and interesting/amusing - "This Guy Can Get 59 MPG in a Plain Old Accord. Beat That, Punk.":


One has to wonder whether same principle can be applied to economics.

I.e. that continous and moderate spending instead of savings somehow keeps the wheels moving in the economy.

This works, but the trouble comes when some guy in a big truck starts heavily tailgating you and flipping you off.

That would be unfortunate, since a heavy truck has the most to gain by not changing speed.

If you want to help traffic, stop hitting your damn brakes so much. Brakes are for strong deceleration, and most deceleration in traffic can be handled by letting off the gas. Once you get good at this, follow as closely as possible in a traffic jam without applying your brakes.* There's nothing better a skilled driver can do to alleviate a traffic jam. The jam is physically shorter and people behind you are less likely to apply their own brakes as a result of these measures.

* This has the added benefit of making for a smoother ride, which also encourages those behind you to ease off the brakes.

Driving in Los Angeles, this is exactly what I do... I'm convinced that most traffic jams are caused by people needlessly applying their brakes and slow cars clogging the fast (far left) lane.

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