Buzz Blog

Jerks actually reduce the risk of traffic jams

Tuesday, July 28, 2009

The next time someone cuts you off on your morning commute, don't be so quick to call the driver a jerk; you may have a reason to say thanks. According to the latest physics research, rule-breakers—drivers passing you on the wrong side or changing lanes too close to the intersection—actually help smooth the flow of traffic for the rest of us.

"The interesting finding is that if most of the people are law-abiding, and you have a certain amount of people who are breaking the rule, then you are actually getting the minimum chance of a [traffic] jam," said Petter Minnhagen, a physicist at Sweden's Umea University and an author of the paper published in the journal Physical Review E.

Physicists at the school uncovered this phenomenon while constructing a computer model of how a crowd of people move across a confined space, such as a pedestrian-only street. They divided the space into squares, like a chessboard, and randomly placed pedestrians in some of the squares. Like real people, the model pedestrians had a certain small probability of momentarily pausing, as if they had run into a friend or had bent down to tie a shoelace.

To make things more interesting, the researchers then tossed a few mavericks into the mix, who didn't follow the rules the other pedestrians used. The physicists ran the simulation over and over, each time boosting the percentage of rule-breakers. At first pedestrian deadlocks worsened. But as more and more rule-breakers joined the fray, something entirely unexpected occurred: traffic flowed best when only about 60 percent of pedestrians were obeying the rules.

Simple interactions of individual cars, people, or molecules add up to large patterns in a system. The high concentration of pedestrians in a small area increases the chances of a jam, but rule-breakers made the crowds spread out.

Morris Flynn, a University of Alberta professor who uses computational methods to study car traffic, agrees with the explanation. Because rule-breakers "carve out their own path," Flynn said, they dilute large concentrations of rule-abiders moving in the same way. He pointed out an example familiar to anyone who has driven on a two-lane road: breaking the speed limit to pass a slow vehicle prevents a long chain of cars from forming.

However, there is one rule you shouldn't break, according to a new analysis of how high-volume traffic flows along a highway. Cecile Appert-Rolland, a physicist at the University of Paris-Sud, looked at the tailing distances between cars traveling on a busy two-lane expressway in the suburbs of Paris. Most people have heard of the "three-second rule" for following distances; after the car ahead of you passes a point on the road, count to three. If you pass the same object before you get to three, you're following too closely. This time-based measure of the distance between cars is what Appert-Rolland terms the "time headway."

Her research showed that tailgating drivers were more likely than a non-tailgater to have a car in the lane next to them, so they weren't just speeding up in order to change lanes. She also found that these short time headways tended to extend across several vehicles, creating a platoon.

"We can identify at least seven or eight cars where they have time headways of half a second," she said. Considering that a driver's reaction time is about one second, these platoons are disastrous pileups waiting to happen. "If the first one brakes, the second one has to brake harder, the third one even harder, and the last wouldn't be able to brake hard enough."

So while unexpected behavior may help with congestion, always follow the three-second rule—because if you're tailgating, chances are you won't be the only one.

-Lauren Schenkman

Posted by Unknown


tmlhkyfn said...

Most don't drive that way however; I explained it to a lady one day & it was like a light went off in her head. Yes I know I am replying to something 10 yrs old

Sunday, June 9, 2019 at 1:17 PM

phoenix real estate market said...

Thank you for your informative post.You are right Jerks actually reduce the risk of traffic jams but, they increase the risk of accidents!!
Thus increasing the risk of "MAJOR" traffic jams! The irony.

Sunday, May 19, 2013 at 3:29 PM

Anonymous said...

Anon 5:49 hit the nail on the head. When traffic is congested, different rules apply. If all drivers instantaneously pass on the left and merge back into the right lane, assuming a constant distance between cars, the throughput of the highway is halved. If cars use both lanes, congestion is eased and throughput is increased. Insisting that all but a few statistical outliers clog up the right lane is not going to ease congestion. And, of course, as exemplified by the ridiculous comments on this page, 90% of the population believes that they are the outlier, which makes such an arrangement unsustainable anyway.

Unfortunately, I do have to admit that tailgating, while not beneficial at all to the individual, is socially optimal excepting accidents. If the average distance from front bumper to front bumper can be decreased by half, the throughput of the road doubles. Still, it's reckless, unnecessary, and stressful for all involved.

In the end, I don't care what the research says. If someone is, god forbid, actually going the speed limit in the left lane, there's no need to tailgate or pass them on the right. Think about your loved ones and their loved ones and just chill out.

Thursday, March 24, 2011 at 1:49 PM

Types of cancer said...

We all make mistakes while driving - but be fair enough to admit a mistake by apologizing. This will take out some of the stress factor in those situations. Use turn lights whenever make a lane change or turn. If the car behind you has to hit the brakes hard to avoid an accident because you made turn without using the turn lights can even result in an accident.

Wednesday, October 13, 2010 at 2:05 AM

Paul the St Albans Driving Instrcutor said...

Tailgating seems to be a phenomenon that has missed the UK. I am a driving instructor and even when i took my driving test ('ahem'.. years ago :)) we were taught the 3 second rule. I teach it to my students now. Trouble is, when on the motorway, you leave a space that big and someone is just bound to jump from the inside lane and fill it!!

Sunday, September 5, 2010 at 12:25 PM

lovin life in Seattle said...

That looks like the traffic in down town Seattle.

Tuesday, August 17, 2010 at 2:22 PM

Jim at home in Phoenix said...

I'm shocked that the rule breakers are actually helping, I would have figured it to be the opposite. It sure seems that way here in Phoenix Arizona.

Tuesday, August 17, 2010 at 2:20 PM

Ajlouny said...

Sounds like the perfect balance...maybe.

Monday, September 28, 2009 at 9:32 PM

Larrry said...

BOTTOM LINE: Get out of the fast lane if people are passing you on the right. Slow cars that stay in the passing lane create artificial delays/backups and decreases the level of service on the roadway ARTIFICIALLY. The average speed of the vehicles behind the jackass is decreased significantly due to only one vehicle. Add another 10 or 15, and you get an artificial traffic slowdown. There may not be another car in front of them for a mile, but there can be 15 or 20 cars packing in behind them awaiting an opportunity to pass the jerk.

Thursday, August 27, 2009 at 6:04 PM

Anonymous said...

Regarding the study, it's interesting. But I have to throw up one cautionary note. Nonlinear dynamic (sometimes called "chaotic") systems - of which traffic is basically one - often exhibit "pockets" in parameter space where the behavior becomes counterintuitive, then intuitive, then perhaps "random seeming", etc., as that parameter is changed. I'm curious what other domains appeared when the rule-breaker rate was higher or lower than that interesting spot at 40%. I didn't see a link to the actual study - maybe it's subscription only (most journals still are). So, as someone pointed out below, the application to the real world may be somewhat different than what you see printed above.

Regarding the FAST LANE/PASSING LANE debate... this is a false dichotomy, and another example of our annoying human need to reduce a continuous variable into binary to simplify the world for our little brains. In reality the description for what various people do in that lefthand lane exists on a continuum. At one end of the spectrum we have the "clean pass". Someone moves into the left lane, speeds up, and then moves immediately back to the right just in front of the car they were trailing. At the other end of the spectrum we have the proverbial Sunday driver hanging out in the left lane forever and going slower than every other car on the road. But in busy interstate traffic situations, the vast majority of the left-lane residents are doing something IN BETWEEN those two extremes (yes, I know this strains your black-white world to contemplate, but it's actually true). Someone moves into the left lane because he is going *generally* faster than the cars in the right lane, and begins slowly but steadily passing one after another of the right lane vehicles. But lo - then along comes one of the "special speeders" (several of whom have posted below), and she/he deems (in his/her absolutist judgment) that that car is not passing enough people per every ten seconds of time, and should therefore disrupt the crowded right lane in order to fold back in. What I'm saying here isn't that one of them is definitively right and the other's wrong, but that things do not fit neatly into "you're fouling things up and I'm not".

Regarding some of the "animated" comments here - I don't believe I've ever seen this much "road rage" occuring, er, off-road before. Chill baby.

Tuesday, August 25, 2009 at 5:49 PM

Anonymous said...

far left lane sometimes is carpool lane, reserved for the few who qualify, and some of course are "jerks" who, yes, drive the speed limit or less, blinker on . . . some good tips in this sequence: late merge, looking ahead beyond the car in front of you, avoiding use of brakes on the freeway

Sunday, August 9, 2009 at 1:26 PM

Mark Gallagher said...

As an auto racer and high performance driving instructor, I can tell you most people mistake being cautious for being safe. Driving is largely counterintuitive and much of what is taught in preparation for receiving one's driver's license is not wrong, it's dangerous!

Friday, August 7, 2009 at 2:17 PM

Per Kjellgren said...

In Sweden it's illegal to NOT move over for an overtaking vehicle, even if that vehicle is breaking the law (or just being a total douche) by overtaking. So yes, the slow driver in the left lane is the jerk. Since most roads have only one or two lanes in each direction this is a very necessary rule.

Monday, August 3, 2009 at 7:59 PM

Anonymous said...

I think it's safe to say that most of the people interested in this article (enough to post a comment) already know the rules and try to obey them while the jack animal in the left lane, going 5 under, with his left blinker on (for miles!)...couldn't care less about the rules or the fact they're creating dangerous situations behind them.

Monday, August 3, 2009 at 2:49 PM

Anonymous said...

I've certainly seen plenty of highways where signs indicate left lanes are for people heading to the next state, and right lanes are for people getting off at the next few exits.

So the left lanes aren't always exclusively for passing or fast driving only. (Though, if two left lanes are for travel to the next state, the leftmost one does still tend to be faster/passing.)

Friday, July 31, 2009 at 6:15 PM

billgo said...

I'm also up here in Toronto. If I'm passing you on the right (in NA), then you are in the wrong lane!

The other thing which ticks me off is that the current speed limits are designed for the lowest common denominator, "mediocre drivers with wandering attention, bald tyres and slippery roads".. Actually they are designed for revenue, and no longer has anything to do with safety..

Friday, July 31, 2009 at 4:41 PM

Anonymous said...

I bike my way to office and my bit of social service enroute is to squeeze into the next available gap on road. But I (uninformedly) judge whom I'm passing by the way he/she is driving lest I get killed for the noble cause.

In India the rule is 'drive on the left of the road'. In Bangalore our rule is 'drive on what's left on the road'!

Friday, July 31, 2009 at 11:23 AM

Anonymous said...

There's one area where this has definitively proven to be true. It's called "late merge". When you're on a multilane highway and a lane is ending 1/2 mile ahead (either because the lane ends or because there's an accident or work zone ahead), DON'T be nice and merge left immediately!! Instead, drive all the way to the end and THEN merge.

I know some people think those "late mergers" are heartless jerks, one step below child rapists. But it actually makes a lot of sense when you think about it in terms of real estate. If every does an early merge, you've got a 3-mile backup in one lane and a whole bunch of wasted real estate in the empty lane. If everyone does a late merge, now you've got two lanes that are each only backed up for 1.5 miles.

PennDOT actually experimented with encouraging this a few years ago. They had a major construction project that eliminated one lane on each direction of an interstate. In one direction they did the standard "right lane ends 1 mile", "right lane ends 1/2 mile", etc.

But in the other direction they put up special signs saying "use both lanes to merge point". At the merge point, the sign said "merge here take your turn". The result: significant, major improvements in how long it took everyone to get through.

This is unsafe under real light traffic flows (say, 3:00 am) when your sudden, late merge could cause an accident. But when it's heavy traffic and there will be a backup no matter what, late merge makes a lot of sense.

So next time, do it. Ignore the honks and the fingers; you're actually helping society out.

Friday, July 31, 2009 at 10:26 AM

Anonymous said...

I drove a cab in New York and San Francisco over a period of 30 years, so I learned some unorthodox maneuvers(these days I only use about 40% of them). So this hypothesis sounds intelligent to me.

The thing to avoid is getting resentful about the bold maneuvers others make. If they can make them without drastically endangering anyone else, then what's the diff?

I generally approve of the slower-cars-to-the- right concept.

Friday, July 31, 2009 at 5:19 AM

Anonymous said...

Jerks actually reduce the risk of traffic jams but, they increase the risk of accidents!!
Thus increasing the risk of "MAJOR" traffic jams! The irony.

Thursday, July 30, 2009 at 10:30 PM

Anonymous said...

The far left lane is for passing and right is travel,and the law. If you are in the far left lane and not passing anyone for a certain distance, you can get a ticket for that!!

There are to many people on the roads that like to play games, and purposely slow up one another. I think it's a control thing?

Thursday, July 30, 2009 at 10:24 PM

djm said...

Wow. Lots of clueless people commenting here and many smart ones, but it's very simple: You stay to the far right most lane unless you are passing. PERIOD.
That allows "faster" traffic to always pass you where they should, on the left.

Think about this. What is "fast" to you? Is that the same thing as "fast" to me? No, that's a subjective argument. No one is going to be right.

There are NOT "fast" lanes and "slow" lanes. There are PASSING lanes and TRAVELING lanes.

Everyone can argue over "fast" or "slow". NO ONE can argue over "PASSING" or TRAVELING. You either are you are aren't PASSING, and if you aren't PASSING, then MOVE THE ^%&!# OVER!!!!!!!!!!!!!!!!

Thursday, July 30, 2009 at 7:46 PM

Anonymous said...

Of course this only works in countries where most people abide to most rules :)
Probably won't work in cities such as Bombay Jakarta, or most east asian cities that makes cab drivers in NYC look like the most decent drivers out there.

Thursday, July 30, 2009 at 12:49 PM

Anonymous said...

Always let faster traffic behind you pass. Then they'll trigger the speed traps ahead, allowing you to continue to speed by, at your slightly lower velocity.

If you're the fastest car on the road and in the lead of the pack, you're probably going to get busted.

Thursday, July 30, 2009 at 12:41 PM

Janne H. said...

Is there any difference between the "rule braking" and just a simple increase of speed?

To me, maybe not. These could be just different labels for the same thing. (I haven't read the original article (here on my mobile phone) though).

In general we can ask, how does the labeled thing present itself WITHIN the system? What kind of verbal description is closest to that? How does that relate to the real thing?

Remember, it's just a computational model that is connected to our understanding with the help of those labels. They might be just vague analogies of the real world phenomena.

Thursday, July 30, 2009 at 9:14 AM