
Can a single car break a traffic jam? - chiachun
http://www.bbc.com/autos/story/20160428-how-ai-will-solve-traffic-part-one
======
logn
I often try the technique of leaving lots of space and going at a slower,
steady pace. One problem is that everyone re-routes around you, and you induce
road rage and traffic weaving. The other problem is that unless it's a
straight stretch of road, you have no idea what speed is slow enough.

~~~
GigabyteCoin
Truckers (professional drivers) do this all the time.

If ever there is a traffic jam on the highway, you will see the big rigs
consistently leaving hundreds of feet of space in front of them.

They also seem to concentrate in the center lanes of the highway for reasons I
haven't figured out yet.

~~~
dsl
Semi trucks aren't trying to calm traffic, they are maintaining a consistent
speed (or rather engine RPM) and gear for fuel efficiency. Drivers are paid
per mile and the further they can go on a single fill-up is more money in
their pocket.

Edit to add: It is a computer telling them how fast to go, usually something
similar to [http://www.scangauge.com/](http://www.scangauge.com/)

~~~
iokanuon
>Drivers are paid per mile

That doesn't seem to be the majority here.

------
cortesoft
This sort of traffic jam dissipation is only applicable to phantom traffic
jams. Here in Los Angeles, traffic jams are caused by too many cars being on
the road.

At some point, every available square foot of roadway is filled with a car. AI
can help limit the amount of extra space taken up by air, but that will only
moderately increase the number of cars that it will take before traffic hits.
That number of cars will be reached, easily.

~~~
cft
AI will eliminate truck night stops, allowing them to be driven 24/7\.
Hopefully more trucks will be moving at night. That should reduce the jams.

~~~
paulmd
Increasing the efficiency of a process also tends to paradoxically increase
its utilization (Jevon's Paradox). So it's entirely possible that automated
trucking will actually increase total traffic volume.

Still though, even a few vehicles "eating traffic waves" can break up a
traffic jam. I've heard the number put at 3-5% of traffic being self-driving
would prevent phantom traffic jams.

So overall I would say that self-driving cars could help reduce phantom
traffic jams, but they may actually increase _real_ traffic jams caused by
overcapacity.

~~~
maxerickson
Tariffs. If people want access to a congested zone, charge them for it.
Dynamically adjust the tariff based on the level of congestion.

Of course people hate this and wail that it isn't fair, but it is among the
more fair solutions to the immediate problem and inflicting traffic jams is
probably not a good way to address economic inequality.

~~~
SilasX
Agree. Tolls (assuming they means the same thing as tariffs) can also create
the critical mass necessary for commuter bus lines to work, thereby allowing
people to spend only a little more than they do now on commuting but get there
faster since the roads are cleared. (The per person effective toll would be
lower on a bus, even if they are charged by size.)

But they would have to be much higher than in most proposals, and they should
be much lower or non-existence during hours when they're not choked despite
the zero price.

~~~
rando18423
So the poor person who needs to get to the doctor should take the slow lane,
and the rich person who wants to get to the next bar faster should take the
fast lane? Public utilities INTENTIONALLY are not and should not be run
according to the principles of profit maximization.

~~~
SilasX
The poor person should take the bus, which could actually be a fast option if
the streets weren't choked at critical times. That's what a sane utility looks
like. (If they're not choked, no congestion charge.)

I'm not a big fan of the mentality that the transportation system should suck
just so we can avoid the rich have better options than the poor. Taken
seriously, that would mean a ban on air travel because the poor can't have as
much.

If you meant emergency vehicles, those always have priority :-p

------
Coincoin
Over here, I noticed it is much more pleasant to be stuck in rush hour traffic
than off peak. At peak hour, people know the game and know they won't get
anywhere faster by cutting and trying to fight for every inch. They tend to
stay in their lane, merge smoothly and all lanes go the same speed.

But as soon as the traffic lightens a bit, idiots just come back to break the
peace. I include myself in those.

------
ianferrel
The game Error Prone is cute, but it mostly shows that it's very difficult to
keep going a constant speed when your only controls are a binary "Full
Throttle" and "Idle".

~~~
Johnny555
Which is exactly how some people drive - an ex- used to make me car sick with
the way she drove - rather than maintaing a constant speed, she'd speed up
'till she got too close to the car in front of her (dangerously close), then
let off on the gas (or even tap the brakes) to slow down.

Annoying and led to no end of arguments "Why are you always criticizing my
driving!?".

~~~
wnissen
With that style of driving, the minimum speed is also far more likely to drop
to 0. And when one person is stopped, everyone behind them is stopped. Even
for people who don't normally drive that way, add in a cell phone and that's
exactly what starts to happen because they don't have enough remaining
attention to avoid being "surprised" by a stopped car.

------
elchief
The trick is to leave enough room in front of you so you don't have to jam the
brakes, but not enough room that some fucker will pull in front of you.

I also try to jump into the left lane at an intersection stop, if there's no
left turner, to let people turn right

~~~
serge2k
> not enough room that some fucker will pull in front of you.

why does it matter, most of the time?

~~~
arprocter
Because then you have to slow down to open a new gap.

And then once you do some other genius pulls into the space.

Repeat for entirety of journey.

------
xbryanx
William J Beaty's video on Traffic Waves (linked in the article) is an
enjoyable summary of some of these ideas:

[https://www.youtube.com/watch?v=iGFqfTCL2fs](https://www.youtube.com/watch?v=iGFqfTCL2fs)

------
talldan
When driving I've also noticed another phenomenon. When reaching the crest of
a hill there's an optical illusion that cars are bunched together. From this
viewpoint the driver can see more of the road and vehicles ahead. My theory is
that this causes a momentary shock or panic, and it often causes drivers to
slam on the brakes, causing ripples of braking behind them.

------
Houshalter
A long long time ago, I stumbled onto the personal website of a guy who was
really into this. He had little simulations of different types of traffic
patterns, and how a single car could break it and return it to normal. It was
really interesting, but I don't have the slightest idea on how to find that
website again if it even still exists.

EDIT: Found in the comments, this may have been it. Honestly don't remember:
[http://trafficwaves.org/](http://trafficwaves.org/)

~~~
furyofantares
This was one of the first sites I remember finding, in the late 90s. Back then
it was hosted on the personal website provided by the author's dialup ISP,
eskimo.com, as I recall.

Edit: I just noticed it still is hosted by eskimo.com, it just has its own
domain now.

------
cortesoft
Every time people try to say we can eliminate traffic if we just leave space
in between cars, I think of this great article:
[http://jliszka.github.io/2013/10/01/how-traffic-actually-
wor...](http://jliszka.github.io/2013/10/01/how-traffic-actually-works.html)

TL;DR there is an effective maximum number of cars that can pass through a
given point of roadway (about 1 car per 2 seconds per lane). No amount of
space-leaving is going to chance that.

~~~
tetraodonpuffer
I think you need to read the update #2 in the page you linked, of course you
can't create capacity out of nowhere, but if you are in a "phantom jam"
situation it does help to "smooth things out" as the page clarifies (which I
think is what this article is about)

~~~
cortesoft
I guess I am just not used to that sort of traffic jam where I am. Here, it is
always just 'way too many fucking cars on the road'

~~~
janekm
In that traffic jam, is 1 car passing that point every 2s? No? Then I guess
your road is not operating at peak capacity.

~~~
cortesoft
That is the maximum number of cars that can pass a given point in 2 seconds;
it does not mean that a road operating at peak capacity can reach that number.

You also have to take into account cars merging onto the road you are on.
Imagine a road acting at peak efficiency, with a car passing every 2 seconds.
Now merge in more cars. They are going to push back every car behind by that
same 2 seconds.

You can read the section on 'merging' in the link above to read more details.

------
mjevans
I want to propose a second more radical suggestion.

I think pacer cars might work very well for phantom traffic jams, but I very
much disagree about /how/ they should be used. Instead of encouraging an over-
capacity jam, I believe that the pacer cars should expressly communicate to
other traffic something along the lines of.

"Temporary" / "Speed Limit" / "Follow at XX"

On a rear message board.

The pacer car would then draw out the stuck traffic in to the space /ahead/ of
the jam and encourage the compression wave to expand to the front instead.

------
piracyde25
Somewhat related to this traffic hobbyist, written on 1998--
[http://trafficwaves.org/](http://trafficwaves.org/)

~~~
Lorin
Somewhat related? It's linked in the second part of the article :/

------
DonaldFisk
Traffic jams are often causes in the way the article suggests, and if you
drive at the average speed, instead of the maximum legal or safe speed
whenever you can, there's a good change the jam will have dissipated just
before you reach it, and you'll get where you want to go just as fast. This
means that the cars behind you (provided it stays behind you) also don't have
to stop. Their drivers should thank you for saving their fuel rather than
curse you for driving too slow.

To minimize fuel consumption, it's best to drive in the highest gear, at the
lowest speed for that gear. Failing that, to drive at a constant speed in the
highest gear for that speed. If you do have to slow down, ease off the
accelerator and change down gears, rather than use the brake. This means
thinking ahead. You can do this when approaching a red traffic light, so that
it will be green by the time you reach it.

There are a few other tricks to save fuel, such as driving at the minimum
_safe_ distance behind a big rig, and using gravity on hills to slow down or
speed up.

This is sometimes called hypermiling: [https://en.wikipedia.org/wiki/Energy-
efficient_driving](https://en.wikipedia.org/wiki/Energy-efficient_driving)

------
jetengine
This game is easy to beat. Wreck most cars except a few, get a single car in
the inner circle by slightly bumping it and press and hold the corresponding
key.

62.8 kilometers covered.

------
feelix
I've always wanted to see what would happen if the government employed workers
(maybe traffic cops) to take up each lane on the motorway, and form a line
that you can't get passed, and drive at a speed just right to unclog traffic
jams during peak hours.

I wonder how much more throughput and time saved we could get just by having
lines of breakers every 50km or so on a highway during peak times.

------
noonshine
I have adaptive cruise control in my Subaru Legacy and I have often wondered
what will happen when more people have ACC. Or even if I were following
another car exactly like mine - would the lag time grow exponentially with
more intense stop/go or would it even out? Or does it depend on how well the
car implements it?

~~~
blakeyrat
The adaptive cruise control in my Ford turns itself off if the speed is low
enough-- which on Seattle-area freeways happens pretty often. So I stopped
trying to use it.

~~~
ahlatimer
The Subaru one stays on until you come to a complete stop. Even then, it's
still "on" in a way, since it'll hold the brakes, but you have to flick up on
the cruise control switch to get the car to start moving again. It'll also
notify you if the car in front has started moving again and you haven't done
anything (with or without ACC on). It's on my girlfriend's car, so I don't use
it every day, but it has been nice the times I've driven it in traffic.

------
mjevans
No, at least not for I-405 / I-5 near Seattle.

These roads, due to a complete lack of effective urban planning and
development, are several times over capacity.

I like to think that this heuristic would be effective for such cases.

* Aim for a hard speed limit (maybe the actual speed limit).

* Actually obey the law of this state: Keep Right Except to Pass.

* ALWAYS allow merges (from either side) with higher priority.

Edit:

After reading the github link from one of the other posts I want to expand why
I disagree and suggest always allowing merges.

It is to allow traffic to leave the freeway (merge right to exit) as well as
to enter the freeway (merge left, mostly to enter at all, but also in case
they're going a long distance or need to get to special use lanes on the
left).

~~~
PantaloonFlames
> Aim for a hard speed limit (maybe the actual speed limit).

That's not gonna work. Depends on the day, the time, the weather, rain, fog
etc. Some days, traffic flows at 70 on 405 during rush hour. If you go the
legal speed limit you will be the dangerous blockage that makes everyone else
down, and makes a few people unnecessarily grumpy. Other days it's misty
because the water on the road gets stirred up by all the trucks. It's
impossible to go the speed limit on these days, the flow is going 45.

There is no hard rule, except: go with the flow. SEE the traffic. BE the
traffic. Do not FIGHT the traffic.

~~~
ThrustVectoring
Enforcing a speed limit on freeways is completely possible. They've got it
done in England. What you need to do is capture license plates on entrance and
exit, and calculate the average speed for each car's trip. If the speed limit
is 50 MPH for traffic-flow reasons, and you do your 15 mile commute in 15
minutes, you're getting a "60 in a 50 MPH zone" ticket in the mail, every
single time.

People will learn in a hurry that speeding is pretty much pointless and self-
harming.

~~~
noarchy
They've really got the surveillance state thing down to a science there, if
they're doing things like that. In North America, where there are cameras,
they tend to only look at your speed at a specific moment.

------
gerbilly
I wonder if we'd have as much stop and go traffic if every car on the road was
standard.

I drive like this just to avoid using the clutch. I'll basically crawl at the
average speed in 2nd gear, until traffic speeds up.

I suspect truckers may be doing it for the same reason, and their gear ratios
mean they would have even more gears to cycle through.

Stop and go would be a huge pain for them if they have to come to a full stop.

------
arprocter
I wonder how much of this is mitigated by good lane discipline?

My SO actually got pulled over the other day (or at least that's what the cop
used as an excuse) for driving in a passing lane when not passing anything. I
said I was glad because it's a terrible habit - every lane ending up going the
same speed as the slowest driver

~~~
gerbilly
>every lane ending up going the same speed as the slowest driver

And if two drivers drive abreast, then it's like having two roads going to the
same place, where no one can pass anyone.

------
sickbeard
Vehicles talking to each other will not break a practical traffic jam. The one
caused because one car had to stop for some reason or other, now everyone has
to stop or slow down in the same vicinity until there are less cars flowing
through the area.

~~~
creeble
I'm not so sure. I think the big difference it would make to have cars talking
to each other is that they can all know where the other (within a local range)
is heading, make interchanges more optimal.

A lot of traffic congestion happens because we have nothing but (too-
infrequently-used) turn signals to indicate our intentions. If all the cars
knew where they were going at an interchange, you could at least optimize the
flow.

Of course, there is _no_ solution when there are just too many cars trying to
fit on a road that can't handle it. And that's probably 80-90% of the problem
anyway :(

------
afterburner
I would avoid blaming any traffic on "non-optimal" driving by other drivers
(not leaving enough space so they maintain constant speed, stuff like that),
since it's just another recipe for road rage.

------
mathogre
I just had fun crashing cars. 25 crashed with 1.8km travelled. I know it's not
the point, but I don't care (nod to Icona Pop). I love it. I needed the laugh.

------
mdotk
Without AI, the answer today is to drive as fast as possible all the time.

------
mannykannot
While, in the right environment, a single driver may be able to break a jam, a
single driver can create one just about anywhere.

------
StillBored
This theory has been running around for a a few decades now. But a couple
years ago I read a paper where they were studying traffic jams, and the
conclusion is that elastic traffic is the problem, and this technique does
nothing really to solve the problem. Instead simply maintaining the exact same
spacing in front/back of your vehicle does a much better job of avoiding and
clearing traffic jams.

------
revscat
This is almost a perfect metaphor for the failings of capitalism, or at they
very least the notion that the singular pursuit of selfish greed can lead to
ideal outcomes. The selfish need for individual drivers to go as fast as they
can leads to a collective failure, here in the form of a traffic jam.

~~~
ctdonath
Capitalists are generally smart enough to forego immediate gain in favor of
substandard greater gains under different conditions.

Rather than drive as fast as I can in Atlanta's 8AM rush hour (and get nowhere
fast in the ensuing jam), I leave for work before 6AM (with half the drive
time).

~~~
darpa_escapee
On the other hand, quarterly profits.

------
stevebmark
Traffic jams exist because humans drive cars, and humans are not designed to
process data at 120 kilometers per hour.

This is a major repost but still misses the main problem. When you look at a
car in front of you, you perceive it as a stationary wall, not a moving wall.
When you slow down, you're trying to avoid hitting where the car in front of
you _is when you press on the brake pedal._ You're not smart enough to realize
that you should be slowing down to avoid hitting where the _car will be_ when
that car stops.

You do this, and you should not be driving cars. Leaving space in front of you
is an inefficient solution to this problem, now you're overcompensating even
more for the problem.

You can try watching one car ahead of the one in front of you to predict when
the car in front of you will slow down and need to stop. Your passengers will
freak out, constantly thinking you're going to hit the car directly in front
of you, because they perceive the car in front of you as a stationary wall. In
reality, you're driving more efficiently.

The day when us unevolved meat sacks stop controlling two ton metal bullets
can't come soon enough.

~~~
to3m
But my car weighs only 1600kg, and for _years_ my passengers have been telling
me I'm going to hit the car directly in front of me. Looks like that day has
already come ;)

