What Causes Traffic Jams? You.

The next time a traffic jam materializes in front of you for no apparent reason, think about Japan. That’s where scientists have, for the first time, recreated “shockwave” traffic jams, in which one driver’s slowing down creates a ripple effect that moves backwards through traffic, grinding everything to a halt for miles. They say recreating the phenomenon successfully is the key to finding ways to defeat it.

Their experiment found that human error is a major cause of these most frustrating kinds of traffic jams (there are, of course, other causes). But if driver error is the source of the problem, don’t drivers also have the solution? Clive Thompson points to one idea, the classic “slow down and keep a constant speed” method, which seems to be effective in breaking these shockwaves. Any other solutions?

Cooper's Dad

I'm reminded of the fact that if traffic lights are synchronized (e.g., consistently green) for traffic paced at 35 MPH, so too are they synced for me to go 70 MPH!


Everyone driving at the same slow speed will not fix this.

IT'S SIMPLE SCIENCE AKIN TO FLUID DYNAMICS. But here's a thought experiment for the lay person:

Assume you have a pipe with water flowing through it at a "full rate", or at 100% capacity. Now put an obstruction in the pipe (like a rock).

What happens? The pipe turns into a funnel and IT BACKS UP. The water slows down to a trickle and is limited at the smallest section: right at the neck of the funnel or obstruction.

The idea that everyone should just drive at the same slow speed doesn't make sense. It still becomes a traffic jam. Unless for some reason you believe driving at 5 mph on a highway is fast.


tailgating tailgating tailgating. if people just allowed enough room they wouldn't have to slow when the guy in front of them messes up, and more importantly, the guy 12 cars back wouldn't have to come to a stop. the ripple effect won't happen if you have enough room.


In my experience, 90% of drivers are incompetent. The only way to prevent things like this, which are caused by incompetence, is to implement actual restrictive requirements for licenses. You can pass any law you want, create any incentives you want, but it won't matter. Most people are *incapable* of driving properly, no matter how much they want to, due almost in entirely to an inability to pay proper attention at all times.

Ultimately we're, sadly, going to have to eliminate human drivers altogether and automate everything. I say sadly, because I love driving, but I accept that I'll have to give it up too, to save the tens of thousands of lives and countless hours in traffic that human drivers cost us every year.

Charles Oliver

Look for a market in everything. If there is supply there will eventually be demand. If supply cannot meet demand you have bottle necks. So if you reduce the number of cars on the road now, unless you make it prohibitively expensive to use the roads in the future eventually you will get back to the equilibrium state where supply and demand are matched and congestion is likely. If it is designed to accommodate a maximum capacity that capacity will be reached and being humans we will most likely exceed it. What would be interesting is to see if you can make it seem like a road is at capacity without actually being there.(capacity that is, to make the road disappear might be a little difficult.)As a long term solution massively mass transit has to be the only way forwards.
ps hat tip to econ2econ


Driving a car should be a much more painful experience. They should cost more to purchase and drive, and those costs should help offset better public transportation, biking, and walking infrastructure for this country - especially in cities where density makes it easier to choose these other modes.

40 percent of all trips taken in urban areas are two miles or less. The majority of these trips are currently taken by people sitting alone in their cars. This country needs be investing more in safer bicycle and pedestrian infrastructure and doing more to encourage people to bike and walk these two mile trips. For the people who can't or don't want to walk or bike two miles, there should be great public transit. Driving should be the last and most expensive option.

It's really going to take multiple approaches to reduce traffic on a large scale including, 1. major new investments in public transit, bicycle and pedestrian infrastructure, 2. giving better incentives to use these modes, 3. encouraging more telecommuting and 4. discouraging automobile use by increasing the costs associated with driving.


Chicago Area Planner

Ahhh! Not tolls! At least not here.
Although I am not a specialist in transporation planning, the chicago area tolls are THE (well, ok, ONE of several reasons) for the back up. You merge 7+ lanes down to 3 and see if that's not a "bottleneck".
I also have a problem with paying your way out of a jam, because it only benefits those that can afford it. If the rich folks want to pay their way out of a jam, unite and build your own road system. I'd like to see the membership fee.
Maybe we shouldn't do anything about jams. The question should be how long are people willing to sit in one? Is a 20 minute trip on an open road worth an hour? Two hours?


slowing down is more of the genesis of the problem. slowing down is necessary in some cases, and error in others. either way it has to happen.

When one driver slows down he can obviously speed back up to normal speed no problem. the reason traffic occurs is because drivers are no good at accelerating at the same rate. People are ok at braking at the same rate because otherwise you will crash. There is little incentive to accelerate at the same rate because the only consequence is holding up those behind you.

so let's be clear, from an operation process standpoint, it is actually the irregularity in acceleration rate, not slowing down, that causes traffic.


Just having big (flashing?) signs that say "KEEP MOVING" or the like would tremendously help


In the UK major urban motorways (freeways ?) have traffic monitoring which sets and displays reduced speed limits as congestion increases. The reduced limits are speed camera enforced - often with 'average speed' cameras which record your licence plate as you enter and leave and catch people sprinting between cameras. Some of these traffic schemes are experimenting with using the 'hard shoulder' (? US equivalent) during peak hours as an extra lane, if not in use by broken down vehicles. London has a 'congestion charge' of ?8 a day - licence plate camera recognition enforced - to make you think about whether your trip is essential. I won't mention the national network of speed cameras....

All of these ease flows and reduce congestion. Without them UK traffic wouldn't work. But here's the thing - they're not enough to produce jam free, sustainable traffic levels. There is a limit to use of the car!



The Autobahn has electronic speed limit signs that denote a different limit for each lane. There are also certain unrestricted sections of Autobahn that still have these electronic speed limit signs. When driving conditions are clear and fine the limit is set high, sometimes unrestricted on the best segments of road. When there are adverse driving conditions, e.g. a traffic collision, heavy weather, etc.; the limit is dropped and is heavily enforced. I believe they utilize speed cameras as part of these signs which will record your speed. This system, to me, provides the best of both worlds: Allowing drivers to drive very fast when deemed appropriate (by the government, not the testosterone dosed adolescent behind his/her 92 Civic SI), slowing drivers down when necessary, and most important of all, making sure that violators of the speed laws are punished every time. This cuts down on the temptation to speed when you know it's for certain that you WILL be caught, not that you might be.



Sorry Roger (#1), but I live in Brasilia, Brazil, where the roads are packed with speed-limiting cameras, and they only make the traffic jams worse. People instinctively slow down because they already know the locations of the cameras, and sometimes they slow down unnecessarily, stepping on the brakes and forcing other people to do the same.

I think I would suggest specific lanes for each kind of transportation; trucks and buses on the right lane exclusively, car poolers on the left (although I doubt that would work here in Brazil...). Here we have trucks and heavy vehicles constantly switching lanes and taking the fast lane, and since they are slower to pick up the pace again once they've stopped, it slows down traffic a lot.


Tolls. My observation is that the Ohio pike through Cleveland is not as congested in rush hour as the interstates through the Detroit metro area are. The Ohio pike has fewer on- and off-ramps, spaced well apart, while the Michigan "free"ways are used to travel as little as a mile from on- to off-ramp.

Another comparison: the run from Indiana to Illinois during rush hour. I-94 is a bad jam while the Lincoln skyway is a cruise - but it costs money.

Sizing doesn't help. All new roads end up carrying greater than design capacity due to new construction, new businesses, etc. If you build it, they will come.


One Word, from the land of the automobile: Autobahn!


Want less traffic? Get rid of the cars.

Problem solved.



I had another idea....

What if each car was equipped with a little factory or add-on device that did the following:

1) Electronically obtained the speed limit for that portion of road/lane (from electronic signs?), and was programmed to understand that the left lane would be for cars doing AT LEAST the speed limit, or some such.

2) Verbally advised the driver (even if it has to shut down the radio) that he/she is going too slow/fast for the road/lane, and advised them to either change lanes or fine another road.

3) Could use laser or doppler effect to determine how fast the traffic ahead is going. If the car ahead is doing 45 on a 70 mph highway, the driver of the car would not be admonished, since they cannot safely go faster. However, the car that is doing 45 (and holding all the others up), since there are no cars in front of it to slow it down (and the laser/doppler woudl determine this), would not only be admonished, but would be electronically warned...and perhaps ticketed...and at the least go into a database where, if this happens on a regular basis, the person is brought before a firing squad

5) Also, this device would caution drivers about maintaining a safe distance from the car ahead, which, as one poster mentioned, causes the ripple effect of back-up when someone brakes.

Also, it could be used by the police to relay traffic messages pertinent to that section of road (again through the electronic signs, perhaps?).



I'm a huge fan of reducing cars as well, but we need a tangible method of doing so.

My proposal - increased incentives for outsourcing work.... to one's home.

Let's see some kind of incentive for businesses that are able to keep employees working at home for the majority of the week. Sure, it won't work for everyone (it can be tough for some to adapt to 'working' in a 'home' environemnt), but for employees that are able to meet whatever performance metrics are set for them, it's a great way to keep certain fixed costs down, and non-essential cars off the road.

How about a low-cost option from private limo services for commuting purposes? Basically a taxi service that provides door to door transportation that is hired by the corporation for its employees. There has to be certain break-even points where such a service would be beneficial for both parties and beneficial from a congestion stand-point.



It's hard driving and keeping a constant speed when I'm on my phone, having a coffee and bagel, and reading the morning news out of NY.


take the train

live closer to town

redesign cities


in crowded cities, double parking is the problem. as steve martin said, death penalty for double parking (it also solves over population growth.)