Do drivers who keep gaps in stop-and-go traffic worsen it? (2012)

https://www.quora.com/Do-drivers-who-keep-extremely-huge-gaps-between-their-car-and-the-car-in-front-of-them-in-heavy-very-slow-stop-and-go-traffic-cause-the-congested-traffic-to-be-worse?share=1

by throwaway000002 • 11 years ago

45 50 11 years ago

quora.com

abdulhaq• 11 years ago

The question is too vague to give a good brief answer. Narrowing it down, I believe that it is possible for a good driver to reduce the stop-go element of heavy traffic by following the car in front at a judicious (more than average) distance and then braking more slowly than the car in front as the traffic in front is reducing speed. When the traffic in front starts to accelerate again the driver then accelerates more slowly until a sufficient distance is achieved between him and the car in front such that the slower braking technique can be used again as necessary. I know from personal experience that it is possible to reduce the stop-start nature of the traffic in this way.

quxbar• 11 years ago

As you turn the dial of driver response time, you're basically changing the congestion function of the road.

Tim Roughgarden has a fantastic book that's very satisfyingly deep, but succinct.

https://mitpress.mit.edu/books/selfish-routing-and-price-ana...

yareally• 11 years ago

The other variable to consider is those that decide they'll reach their destination faster by cutting one car in front of you when you are keeping some distance. I see this happen a lot in traffic and sometimes results in nearly having an accident.

kbenson2• 11 years ago

As someone who tries to do this whenever possible, it can be largely for naught if cars in the bordering lanes see the gap you've allowed in front and move into it. :/

firebones4• 11 years ago

If you expand the "leave a gap of 2 seconds" rule to instead follow the car in front of you by 3 seconds, then someone cutting in should only require you to add 1.5 seconds of distance to the new, smaller gap. And since the car cutting in will often tailgate the car in front of you, it's often really around 750ms you'd have to bleed off, which shouldn't require much speed change.

mirimir4• 11 years ago

Sometimes I also cut off such interlopers. I can accelerate quite rapidly in first. After a while, surrounding drivers learn to respect that space in front of me.

chm• 11 years ago

I used to commute by car for about 40 minutes to an hour each way. I got pretty good at avoiding "stop and go" without leaving too much space between my car and the one before me.

Some useful practices I developed:

Don't look at the car directly in front of you. Stare through its windshield if possible to get an idea of what the car second in line is doing. If you can't see through the windshield, try looking at its shadow. And if you don't see a shadow, look under the car right in front of you: you should be able to see the first car's lights illuminate the pavement and guess what it's doing. When it's raining, that is especially easy since the pavement is much more reflective.

Also set your mirrors in such a way that creates a "single" mirror. Where the proximal end of your left mirror ends, the proximal (left) end of your cabin mirror begins. Where the distal (right) end of your cabin mirror ends, the proximal end of your right exterior mirror begins. This eliminates the need to look behind you every time you want to switch lanes. It doesn't eliminate your blind spot, merely moves it, but that's only a problem if someone is making a 2-lane change. That's usually pretty rare in heavy traffic.

Of course, all of these tricks don't work when others drive too erratically. If you don't gauge the distance between you and the vehicle right before you, others will 100% jump at the chance to cut you.

mirimir4• 11 years ago

Don't look at the car directly in front of you. Stare through its windshield if possible to get an idea of what the car second in line is doing.

Yes! Also, when it's darker, you look for brake lights way ahead. That's also a marker for speed traps.

jrs2352• 11 years ago

An interesting site: http://trafficwaves.org/trafexp.html

baldfat2• 11 years ago

You stay with in 3 seconds so like 25 feet in most traffic NOT 1000 feet!!!

It is all about how many cars flow through a certain spot a minute. If you have space you have more time therefore creating MORE traffic behind you!

If I had a billion dollars this would be a Super Bowl Commercial and I would blast YouTube and FaceBook with ads.

abduhl• 11 years ago

I'm upvoting you so that others can see an example of incorrect thinking for traffic problems.

Throughput is only one goal for traffic. One can see immediately that a minute of flow at 15mph is equivalent to a minute of stop/go traffic at 30mph equally divided. Similarly, a minute of flow at 15mph is less than a minute of stop/go traffic at 45mph. The latter is NOT the goal of a congruent traffic system because it will result in decreased safety. Eliminating gridlock is a priority for all traffic engineers.

The more important goal for traffic is safety. It is also immediately evident that constant, predictable traffic patterns result in lower accident rates than unpredictable changes like those found in stop and go traffic. Stop and go traffic encourages tailgating, aggressive lane changing, and aggravated driving.

The phrase "you have more space you have more time" does not imply "MORE traffic". It is actually the people driving with this type of mindset that create the traffic, not the person in front.

jessaustin• 11 years ago

If I had a billion dollars I'd hire a driver.

baldfat2• 11 years ago

So I got down voted for saying having more space causes more traffic? I really am confused????

So the down votes are for the desire that people INCREASE the distance between them and the car inf ront when the speeds drop?

metanoia• 11 years ago

When I'm in LA and it's stop-and-go traffic, I find it's best to follow the trucks in the right lane. I average a much higher speed because they don't have the ability to tailgate and slam on their brakes like the most aggressive drivers in the fast lane who are actually causing the traffic jam, and consequently go an even 15 mph as opposed to 0-30-0-30-0, etc.

mirimir4• 11 years ago

I strive to maintain a constant speed, so the gap in front naturally gets larger as traffic ahead speeds up. Back in the day, when I was typically in a hurry and driving insanely, I liked large gaps because I could slalom through them at high relative speed. I don't do that anymore. I hate it when bikers blow through at 100 kmph relative speed. But at least they're small.

Edit: I also hate it when bicyclists blow through city traffic at 10-20 kmph relative speed. For some reason, I'm more afraid of accidentally hurting them.

jackweirdy• 11 years ago

Though eventually, flat.

firebones4• 11 years ago

This may be due to there being more cars exiting the freeway from the right lane. Also, intuitively, drivers often tend to bear left to get to the "fast" lane, but as they defect to the left lane, it frees up the center lane in a similar fashion as exits free up the right lane.

My compromise in a three-lane situation is to always favor the center lane in congested traffic, especially prior to an upcoming exit. If traffic starts to move, I can move left since after the exit, the missing cars will be starting to merge back in (and to the left, negating the advantage of the center). If traffic doesn't move, I tend to just maintain center lane.

Impatient, frequent lane changers always add risk to themselves and others because they're bouncing back and forth between left (the fast lane and the way things "should" be to them) and the right (which routinely frees up as people exit). They tend make it to where they're going faster, but I don't necessarily think it is worth the risk.

legohead• 11 years ago

While most of us academics may be familiar with the problem here, it's moot in the end. No amount of education or public awareness will fix this. Our only hope are self-driving cars or other forms of transportation -- train, hyperloop...

0xdeadbeefbabe• 11 years ago

Will we see a Ballad of John Henry about the last driver?

ArkyBeagle• 11 years ago

I find that simply following proper protocol in traffic rubs off on other drivers. It seems that way anyway. I don't think it's that hopeless. I think most "public awareness" initiatives are pretty hopeless, but my own experience leads me to think that this is tractable. People can learn new mental cost models.

I have personally witnessed the basics of this taught as part of a driver safety course, and most of the people who took the course at least made noises like they were surprised at some of the more intuition-challenging aspects.

jameslk3• 11 years ago

My hypothesis is that the problem becomes worse by at least a few other's impatience and greed. There might be some educated individuals on the road who try their best to do what's said to lead to better traffic conditions, but its the few that ruin it in the end. A tragedy of the commons.

civilian2• 11 years ago

No way, the checked-out drivers cause a ton more problems than aggressive drivers. If all drivers properly sorted themselves by desired speed from left to right we'd have much more efficient highways.

I'd also make the argument that the people who stubbornly don't get out of the way of tailgaters are at fault for creating slow road conditions, and share the blame for a dangerous driving situation. If someone behind you wants to go faster, get the fuck out of the way. And it's not even my preference-- in WA and OR it's literally the law that slower traffic should move right, but I've never heard of anyone being ticketed for it.

ilyanep• 11 years ago

I wonder what would happen if the National Ad Council just started producing billboards that said things like "LEAVE FOLLOWING DISTANCE FOR FASTER TRAFFIC" and "ZIPPER MERGE IS MOST EFFICIENT".

vectorjohn5• 11 years ago

Yep. It's the tragedy of the commons, or some such game theory problem. If you leave a gap, someone switches lanes to fill it. Then you back off to make a new gap (as do they, if they switched lanes with only a few feet in front of them), at which point someone switches lanes.

I still do it, because on average I can keep a good gap in front of me, but I have a feeling that's a big part of why it seems like nobody does it.

civilian2• 11 years ago

I don't think it's even a game theory problem, because most of the actors aren't even rationally looking at their options.

In the Pacific Northwest, maybe 20% of drivers are trying to make any decision that will help them. Maybe another 20% are trying to do the best for themselves as long as it doesn't harm the global traffic state. The last 60% are checked out and are barely paying enough attention to not crash.

bunderbunder• 11 years ago

I think it's fixable, but only at great expense.

I have no science behind this, but I've driven in enough places to notice that there are broad cultural differences in how people drive. I don't think the difference is just in the people. It's also in the civil engineering.

For example, some places are very consistent about having nice long on-ramps that give drivers plenty of time to negotiate a merge without too much hassle, and entrances and exits are always placed on the right-hand side. My impression has been that these cities tend to have very sane drivers. Fewer traffic jams, too.

Others have exits and onramps on both sides. The ramps are often short, and you might even have the occasional short ramp with a tight curve that forces drivers to enter the highway 15-20MPH below the speed limit. These cities force a number of perverse behaviors that make driving problematic. It gets slow drivers out of the right lane because that lane is downright frantic. It also actively places drivers who prefer to drive at wildly varying speeds in the left lane, so now you've got people trying to find their place from both sides of the road at the same time. These combine to encourage a lot of passing on the right, which further mixes drivers who like to go at different speeds across all the lanes. And all that jockeying begets further jockeying, since one starts to feel like they have to drive aggressively just to hold their own.

Against that kind of backdrop, which seems to be the way American cities actually prefer to arrange themselves, I do think that no amount of education or public awareness could ever fix it. You can't create an environment that actively punishes people for behaving how you want them to, and expect them to behave that way anyway.

jameslk3• 11 years ago

I used to leave wide gaps, but then I found that market economics started to apply and my gaps were just filled by other drivers looking to arbitrage my attempts at stabilizing the economy. Making matters worse, they would just cut me off when their lane slowed, causing the market to suddenly crash in my lane. So now I leave no gaps.

skybrian• 11 years ago

The key is to be happy that you're helping other people change lanes more easily (often a hard thing to do in traffic). It's not going to make much difference in your arrival time.

jameslk3• 11 years ago

I can't remember the last time I was happy sitting in traffic, or feeling empathetic. If I have to slam on my brakes because others are feeling particularly opportunistic, it will only lead to cynicism.

Retric• 11 years ago

Don't forget a reasonable gap can significantly increase your fuel economy and how long your breaks last. Remember every time you break that's costing you money.

mirimir4• 11 years ago

I have a manual transmission, so it's also clutch wear. Plus I get tired of shifting.

xellisx• 11 years ago

And for me, not making myself motion sick.

patcheudor• 11 years ago

I must admit. People leaving wide gaps in city traffic drives me nuts. Why? Turn-lanes. People will leave huge gaps and slow well in advance of stop-lights, causing people behind them who want to turn into the left or right turn-lanes to miss the light. The worst are the people at a light, who, with cars to the left and right decide it's prudent to leave five car lengths between themselves and the car ahead of them at the expense of everyone behind who just wants to get into the turn lane so they can make the light.

vectorjohn5• 11 years ago

The gaps really should be speed dependent. So when you're going 20mph, you will have a smaller gap than if you're going 60.

And that applies to stopping, where you should (IMO) have very little gap. For the exact reasons you mentioned.

ColinCochrane• 11 years ago

Here's some evidence that creating those wide gaps does help.

http://www.slate.com/articles/life/transport/2011/10/rolling...

delinka• 11 years ago

There's always a wide range of gaps in stop-n-go traffic. Anything from a car length to 1,000 feet. It's the 1Kft gappers that seem to bring out the crazy in other drivers.

Tangent: how about the drivers that think we should all be merging one entire mile before the merge point and therefore start straddling two lanes in an attempt to prevent passing in the empty lane?

We're supposed to use all the pavement and then zipper merge at the merge point. This would be even easier if traffic would be consistent about gaps.

firebones4• 11 years ago

Zipper Merge to the rescue!

http://www.dot.state.mn.us/zippermerge/

jrs2352• 11 years ago

I wish people would understand the zipper merge and that people shouldn't form a long line since that pushes the congestion further back possibly through intersection and traffic lights causing gridlock which pushes the congestion to streets going perpendicular to the road with the merge. The problem is people think you're "cutting" if you stay in the non-blocked lane up until the merge point and then won't let you in.

sandworm1013• 11 years ago

No. Please leave lots of gaps ... ones just long enough for my motorcycle to sneak into. In all seriousness, in many parts of the world it is natural for two-wheelers to filter past stopped cars to fill every available space in stop and go traffic. Given that bikes fit more people into a given space (pushbikes and motorcycles etc) having the cars leave gaps while stopped can be more efficient. But only where there are enough bikes willing to filter, which is rare in north america.

What is really interesting to me is the math behind leaving extra space in moving traffic. I have to cross a major bridge every day (Vancouver, Lions Gate Bridge) which is often only one lane for my direction. A driver leaving 5 or 10 seconds worth of space impacts everyone behind them. 10 seconds x 350 cars means that one person leaving too much of a gap is actually creating an hour's worth of delay.

vectorjohn5• 11 years ago

One person leaving too much of a gap doesn't create 10 seconds x 350 cars delay. They add 10 seconds delay. You'd only get that hour if everyone had a 10 second gap.

And nobody leaves a 5-10 second gap. That's huge. The DMV recommends something like 2-3 seconds.

sandworm1013• 11 years ago

You missed the point. I didn't mean they delayed any one person by an hour. They are delaying 350 people each by ten seconds ... a cumulative delay of an hour.

10 seconds on a bridge is not unusual. They are normally people looking at the view.

The kids around here are taught to "Increase your following distance ... to four seconds in bad weather conditions." In Vancouver, that is a not-small amount of the year.

http://www.icbc.com/driver-licensing/Documents/drivers5.pdf

At 75kph (normal speed on a rushhour bridge) 4 seconds means an 80 meter (90yard) gap. If everyone left such a gap any city would grind to a halt.

GhotiFish• 11 years ago

I've had numerous debates about this, I've asked someone who works for my local municipalities traffic office about simulations regarding this (though she didn't have the correct simulators to do it, just for intersections).

I know the theory, but people frequently and incorrectly state that emergent traffic jams are proof that leaving large gaps to smooth traffic behind you improves traffic flow. That to me this is an unacceptable leap of logic. Why are their no contrasting simulations showing traffic flow with and without these "smoothing" agents? Creating a simulation that has rolling traffic jams, introduce agents that disperse the traffic jam (can you actually disperse these traffic jams anyway? Again, not demonstrated in the story.) Has throughput increased? It's not a given that it has.

My concern is that the people who tried to do what I am saying only achieved negative results, so they did not publish. Regardless of my concerns, I believe this theory might be true. Which is why this is so frustrating!

dynomight• 11 years ago

I've often thought about traffic flow when stuck in traffic. I'm in favor of a bit of a gap. I'll try to describe it. I'll start with what lead me to my conclusion.

At a stop light that has turned green all the cars do not go at once. They all proceed sequentially from first to last. If the line is long enough, and the light short enough, the last car cannot make it through. If all cars were to accelerate at the same time simultaneously like a train then many more cars would make it through the light. Of course this will never happen with human drivers.

I believe keeping a reasonable buffer in traffic helps prevent the above situation that I see occur at lights. The delay of this affect is repeated for each and every stop.

I think an excessive gap would make the flow worse in the way described in the article. I'm thinking there's a happy medium somewhere. Somewhere between the excessive gap of the one that wants to teach everyone the 'wisdom' of the gap and the hot-heads that want to drive over the person in front.

Do drivers who keep gaps in stop-and-go traffic worsen it? (2012)

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