Suppose we push constantly
ahead, change lanes to grab a bit of headway, and always eliminate
our forward space in order to prevent other drivers from "cutting
us off". If tiny traffic waves appear, we will rush ahead and
then brake hard, leaving larger waves behind us. Repeated action
causes the waves to grow huge. Ironic that the angry people who
push ahead as fast as possible might unwittingly participate in
"amplifying" the very conditions that they hate so much.
The solution seems obvious: drivers with a smooth "calm"
style will tend to damp out the waves and produce a uniform flow...
and the few drivers who intentionally drive at a single constant
speed will wipe out the waves entirely.
MORE EXPERIMENTS
I rarely commute on 520 where the good traffic waves appear. I started
to miss the opportunities to cancel them. However, I soon realized
that the same process could be used to affect the smaller traffic
jams too. "Traffic waves" are simply a series of small
traffic jams with even spacing. Each little jam is destroyed when
a large empty space approaches it from behind. If no new cars are
feeding into the jam from behind, yet cars are leaving from the
front, then the jam is eroding away. If the jam is small enough,
or if the empty space is large enough, then a single car can entirely
annihilate the jam, as I had done with traffic waves.
Now I remember something from years back. When trapped in one of
those "rubbernecker slowdowns", I always tried to accelerate
like mad when I escaped at the end. I figured that if everyone did
this, then the slowdown would evaporate. Yet this did no good, because
the car ahead of me blocked my move. It would not accelerate. I
could never force the cars ahead of me to stomp on the gas too,
so I could do little to aid the "evaporation" of the traffic
stoppage. Aha! I could control the people behind me by slowing down,
but I couldn't control the people in front of me by speeding up.
Therefore, I can smooth out a small traffic stoppage. I just have
to acquire a huge empty space long before I approach it. But if
I'm already inside the jam, I can do nothing to aid the "evaporation"
at the far end. If I cannot predict where jams will arise, then
I'd better drive all the time with a huge empty space. (Which is
just what many truckers do. Did they figure something out that I
didn't know?)
Just one single car, if it decelerates while approaching a jam,
can change the behavior of everyone behind it. And soon these people
behind that single car will take the place of everyone in the jam.
Your single car can bite a huge chunk out of the region of stopped
traffic. If one car refuses to pack together with everyone else
to form a "parking lot," the jam can be made smaller.
Or if one driver gradually builds up lots of empty space before
encountering the slowdown, perhaps that driver can "eat"
the whole slowdown just as the many traffic waves were "eaten"
by my own car.
STANDING WAVE
A"rubbernecker slowdown" ...without rubberneckers! Traffic-waves
need not drift backwards. Sometimes they sit in one place. Once
this type of traffic wave is established, it can last nearly forever.
New cars MUST slow down as they enter, and that's what makes the
wave persist. You cannot dissolve the slowdown by accelerating out
at the end, since you're still blocked by the driver ahead of you.
The solution: bring a huge space in as you approach it. This temporarily
cuts off the flow of incoming cars which feeds it and keeps it alive.
A single driver can easily erase a small slowdown.
On my evening commute on I-5 southbound from Everett there is always
a right-lane traffic jam at one of the Lynnwood off-ramps. Close-packed
cars must crawl along at 2mph for a very long time. Therefore I
intentionally changed to the exit lane as I approached that distant
jam, and I started letting a REALLY huge empty space open up ahead
of me. By the time I hit the jam, there was maybe 1000ft of empty
road ahead of me. Sure enough, my big empty space stopped traffic
from feeding it from behind, while the front of the jam kept dissolving
as usual. By the time I arrived, the jam was about half the size
it had been. Amazing. This wasn't any little traffic wave, yet one
single driver was able to take a huge bite out of it.
Just moving jam around.
Obviously my actions did more than just reduce the size of the jam.
In order to create the empty space, I was temporarily driving about
10 mph below the speed of the heavy traffic. I did this for several
minutes, and therefore I caused a slight slowdown behind me. After
I arrived at the jam, the jam was smaller. When all was said and
done, part of the dense traffic jam had been removed. However, it
was changed into a mild slowdown, and it was spread backwards upstream
over several miles of traffic. Traffic behavior was changed. Rather
than driving at 50mph only to crawl along through a traffic jam
for several minutes, everybody was now driving at 40mph for a few
minutes before the jam, but then having a much smaller traffic jam
to endure. The average traffic flow probably remained unchanged.
But the nasty, frustrating part of the 2-mph jam was converted into
a large "fuzzy" area of reduced speed. And after I made
these changes, drivers as a whole would find it much easier switch
lanes to avoid becoming trapped in the jam, since the solid-packed
region was much smaller. If I had done it correctly, I could have
erased the whole jam, transforming it into many minutes of slightly-slow
driving for everyone behind me. (If I could have started 30mi upstream
of the jam, maybe I would have only needed to drive 3mph slower
than traffic... that is, if other drivers didn't simply go around
my slow car.
Another thing that happened: by shrinking the region of solid-packed
cars, I made it easier for other cars to merge into the exit lane,
so I probably removed part of the jam in the through-lane as well.
The jam was mostly caused by drivers trying to get to the exit.
Drivers already in the exit lane weren't letting anyone in, so the
merging cars sat unmoving in the thru-lane, waiting for a space
to open, and stopping everyone behind them. By inserting a large
empty space, I wasn't only taking a bite out of the jam ahead of
me. I was also easing the jam in other lanes. The traffic jam was
like downtown city "grid-lock," and I was breaking up
the gridlock by putting spaces between all the cars."Anti-traffic".
ANTITRAFFIC DESTROYS TRAFFIC
Here's a general principle I take from the above.
I guess it's obvious in hindsight! Empty spaces can eat a
traffic jam. While I was slightly slowing down to allow a space
to gradually open up before me, I was creating a pulse of "antitraffic"
ahead of me. When my antitraffic finally collided with the dense
"traffic" of the jam, the two annihilated each other like
a positron meeting an electron. It's nonlinear soliton physics.
The soliton waves destroy each other, leaving only a slight fuzzy
smudge behind.
My next thought: if I took several friends along on my experiment,
we could have repeated the same jam-erasing process. Each of us
could have allowed a big blob of anti-traffic to appear, and then
the repeated impacts of the antitraffic could have completely erased
the traffic jam at the Lynnwood exit. When traffic is sparse, we
cannot keep a large space ahead of us, since it's too easy for cars
to pass a slightly-slow driver. But several separate drivers could
bring less-enormous spaces along with them, and any traffic jam
would succumb to the barrage of "antitraffic."
Another lesson I learned: plan ahead. Plan WAY ahead. When stuck
in traffic jams, I discovered that I cannot affect them by "peeling
out" after I'd made my way through the jam. I hoped to make
the far end of the jam dissolve faster. It never worked because
I couldn't get rid of the slow guy ahead of me. But if I'd planned
way ahead and brought a big empty space along with me into the jam,
I could use that space to manipulate the jam. I can control the
traffic only by applying the brakes. Once I get myself packed in
with everyone else, I can do nothing. In order to have an effect,
I must behave differently BEFORE the jam, not while trapped inside
it.
But won't other drivers simply go around me and fill my big empty
space? Hmmmm. After trying this many times, I find that they usually
don't. I wonder why?Ooops! Damn!
While doing all of the above, I once caught myself behaving normally
and creating a huge traffic wave. What a hypocrite! Bad habits die
hard.
Traffic was heavy and I was in the left lane. I had to merge across
several lanes in order to get to my exit. I merged right once, but
the next lane was packed solid (but it was still moving, not jammed.)
Nobody would let me in. I drove like this for a long while, then
started driving fairly slowly in order to drift backwards along
the lane. I found a slot and got in, but now I had to merge right
once more. Many minutes had passed, and my exit was coming up. The
right lane was packed solid, NOBODY WAS LETTING ME IN. I drove slower
and slower, and in a panic I finally forced my way into a small
gap, making the guy behind me jam on brakes. After awhile I realized
that I had just created a huge traffic wave with my behavior. Just
like any rubbernecker I had suddenly slowed way down for no good
reason. But I had an excuse, I had to get to my exit! To make matters
worse, I had nearly come to a complete stop, and brought two entire
lanes of traffic to a near halt too. I probably left a long-term
traffic wave at that spot on the highway. But it wasn't my fault!
Yeah, suuuure.
In stewing about this I realized that EVERYONE has this same problem:
an inability to merge in dense traffic. Others were probably doing
the exact same thing that I did, and this would make the "wave"
near the exit worse and worse. Our inability to change lanes would
create a "dynamic bottleneck" which hovers near the exit.
Obviously the simple cure is to give up; not merge, and miss the
exit. I should never have forced the issue, I should have let my
exit go past. And so should all the other merging drivers. But there
is a bigger issue here. People SHOULD be able to merge. Why was
traffic packed so tightly? One obvious reason: to punish the idiots
who will jump into any little space. I had always done the same
myself. I never allow a space to appear ahead of me, or some other
driver will immediately swerve into it during their quest to cheat
by running to the front of the line. But this sort of "closed-gap"
driving would also prevent any necessary merges at off ramps (and
at on ramps too, of course.) By eliminating the space ahead of me,
I become part of the impenetrable wall which creates the "dynamic
bottleneck" and screws up the traffic at highway ramps. The
gear teeth cannot mesh, so the whole machine grinds to a halt. The
"zipper" becomes jammed because the "teeth"
of the zipper are resentful about new teeth moving into the space
ahead of them.
The jammed mergine lanes are almost like gridlock in a city. City
drivers know to never block intersections, since blocked intersections
will freeze all traffic. But we highway drivers are ignorant. We
close up the gaps when others need to merge. And our behavior creates
needless "highway gridlock" during every single rush hour.
So, if I keep a few cars worth of space open ahead of me, not only
can I use it to help vaporize waves and jams, but I also eliminate
one of the major causes of waves and "highway gridlock."
I eliminate the "solid wall" of traffic at merge areas,
and let people merge without slowing down and creating traffic waves
behind them. Take a look at this animation on page three of this
article. Ideally a merge-area will act like gear teeth. But suppose
that everyone starts defending themselves against opportunistic
drivers by eliminating all gaps in traffic. In that case the valid
merges cannot take place either. A fight develops, and a traffic
jam is created. The jam appears at the merge zone, while a huge
region of empty roadway is created downstream. Sometimes this jam
is the fault of people like me who panic while missing their exit
and who come to a complete stop. Sometimes the jam is the fault
of the huge blinking yellow arrow which blocks one entire lane of
traffic during construction. But the traffic jam is ALWAYS the fault
of those who refuse to let anyone merge ahead of them. "Just
merge behind me." No, that doesn't work, since the guy behind
you doesn't want any merges either. Everyone in the whole lane is
saying the same thing! Delusions of Grandeur.
Seattle suffers from many separate rush-hour traffic jams. Why should
I stop with the jam at the Lynnwood I-5 exit? With enough people
(maybe with cellphones and GPS units), we could intentionally smooth
out ALL the traffic jams on all the main Seattle highways!
This is all fantasy at this point. It's probably illegal for several
people to "conspire" to mess with traffic patterns (would
we be arrested under a drag-racing law?) This could be a "flash
mob" organized via email.
[NOTE: IN TORONTO, TO PROTEST THE LOW SPEED LIMITS, SEVERAL PEOPLE
FORMED A ROLLING BARRIER DURING RUSH HOUR. THEY DROVE AT JUST UNDER
THE SPEED LIMIT FOR HOURS, CREATING A HUGE SLOWDOWN. THEY WERE ARRESTED
BUT LATER RELEASED WITHOUT CHARGES.]
And while it is possible for a single driver to have huge effects
on traffic patterns, some things can't be done by a few people.
For example, suppose I want to eat the entire I-5 and I-90 traffic
jam south of the city. I would have to go all the way to Tacoma,
then drive north. But if I tried driving slightly slow, a space
would never open up ahead of me because nothing stops other drivers
from passing me. In my experiments, I could create my "antitraffic"
spaces only because traffic was very heavy, and because only a very
few people had the opportunity and the ambition to leave their lane
and move into my empty space.Rolling barriers made of State Troopers.
OK, so here's how to dissolve a major interstate traffic jam. Start
many miles upstream from the jam. Put a row of State Trooper vehicles
across the road and have them drive towards the jam. They drive
perhaps at 55 rather than 70 as everyone else had been driving.
Nobody can get by them, and so all the traffic behind the State
Troopers is moving at 55 or so. In front of them a vast space opens
up. After many minutes, the traffic which had been feeding into
the city traffic jams simply stops arriving. There is no new traffic
for many minutes. The huge jam trickles away. Just as the last of
it is gone, the row of State troopers and the 55-mph traffic arrives,
and the jam has been transformed into miles and miles of slightly
slow traffic upstream from the old location of the jam.
THE BIG QUESTION
But does this increase the throughput of the highway? YES!!! It
allows people to merge again! It actually changes the 'capacity'
of the highway. It wipes out a 'dynamic bottleneck.' By removing
the close-packed region, the two lanes of traffic at the exits and
entrances are able to merge... so even though the close-packed region
is now a big fuzzy slowdown, the flow of traffic does greatly increase.
On the other hand, the situation is not so simple if lots of extra
traffic is entering from numerous on-ramps. The "rolling barrier"
can't affect these extra inputs, and if nearly all of the traffic
is from on-ramps, then the "rolling barrier" idea would
be worthless. In that case it can only control the main highway
and not all the on-ramps.
Ah, but what about "rubbernecker slowdowns" at accident
sites? A rolling barrier could let the slowdown evaporate, and change
it into a wide area of slightly-slow traffic a few miles upstream
from the accident. Would the slowdown re-form? Would rubberneckers
hit the brakes and re-create the "traffic standing wave"?
I dunno. Sometimes "rubbernecker slowdowns" persist for
hours after the accident has been cleared. This suggests that the
slowdown is self-perpetuating.
Rubberneckers only trigger it, but they don't keep it going afterwards.
If so, then "erasing" the slowdown might be worthwhile,
because once it's erased, it will only re-form very slowly (or not
at all). If the slowdown normally persists for several hours, yet
it only takes half of an hour for the police to erase it, why not
erase it? True, the slowdown is not "gone," since it has
become a wide area of slightly slow traffic. However, over many
months of slowdown-erasure, this could prevent lots of fender-benders
and road-rage incidents, and eliminate thousands of man-years of
anger and frustration.
Also, the average speed and traffic throughput on the highway MIGHT
actually improve if region of stopped traffic could be removed.
"Removing" the jam just spreads it out and does not immediately
alter the average speed. However, improvements in speed might be
more than you'd expect. After all, things are not "linear"
in traffic flow, since those who sit at 0 mph for many minutes in
a jam cannot compensate by driving at 120MPH afterwards. Also, some
jams act like "virtual bottlnecks" which create huge backups
behind the jam while also creating empty highway downstream. Removing
the jam will remove the bottleneck and increase the flow. (Note:
if this is common, if jams commonly act as bottlenecks, it means
that highways don't have a known capacity. The highway's maximum
capacity is different whether a jam is present or not.)
A ONE-MAN MULTI-LANE
ROLLING BARRIER
In driving with huge empty spaces during rush hour, I find that
the space ahead of me doesn't just instantly fill up. Other drivers
don't change lanes to fill them. Weird! What's going on? First,
if I'm driving with a big empty space, sometimes the car directly
behind me will pass me. Sometimes it happens twice. But this removes
the lane jumpers from behind me, and forms a row behind me of nonaggressive
drivers. Those drivers are like a plug, since any aggressive drivers
several cars back can't even SEE the big empty space ahead of me.
But what about the adjacent lane? Won't they all fill my empty space?
Nope. A few do change lanes, then they rush to the end of the empty
space. This filters out the aggressive drivers from the adjacent
lane, letting them move to my lane at the end of my space, and leaving
sane ones next to my empty space. They don't change lanes. They
don't care that there's a huge empty space growing and shrinking
right beside them. They form a big plug, and aggressive drivers
behind them cannot get to my big empty space.
This "plug effect" only happens when traffic is highly
congested. When traffic is light, I can't maintain a big empty space,
since aggressive drivers can easily swerve around to jump into the
space. But when traffic is light, there's no traffic jams, so there's
no need to create an antitraffic bubble and perform jam-busting.
MAKING A REAL
DIFFERENCE
During a year of practicing the "wave-smoothing" driving
habits, I kept looking for places where I could make a big difference
in traffic flow. Yes, I could always use an empty space to move
a piece of the traffic jam to another location. With a big empty
space, I could even spread the cars apart as I moved the slowdown,
the same way I did it with the jammed sections in the "traffic
wave." But the genuine "bottlenecks" seemed all too
rare. Then finally I noticed that there was one common situation
where I could do some real good.
If you drive in heavy highway traffic, you've probably seen a traffic
wave develop at a construction site where one lane is blocked. You
crawl and crawl at 3 mph until you get to the bottleneck, then you
take your turn merging as the two lanes sloooooooowly come together.
Then you race off at 60 mph! No downstream congestion! The merging
lanes formed a terrible bottleneck, yet the open lanes ahead were
not a bottleneck. A "traffic wave" develops at (and behind)
the merge-zone. After the bottleneck, it's clear sailing.
BUY WHY?
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.
Traffic jams develop at a merge zone whenever the cars get so close
together that there are no gaps between them. Without gaps, nobody
can merge, and so the traffic suddenly comes to a near halt. The
"gear teeth" jam up, the "machine" halts, and
a bottleneck is created. The pile of pebbles can no longer pour
through the funnel. Traffic on the highway turns into a city street
intersection, where people merge at a "four way stop sign."
But whenever traffic comes to a near halt, people always pack themselves
together.
Huh. This is screwy. At the place where the lanes merge together,
close-packed cars cause the bottleneck, but... the bottleneck is
the CAUSE of the close-packed cars... and the close-packed cars
keep the bottleneck in existence. And the bottleneck makes drivers
all pack together.
But, but...
Do traffic jams CAUSE THEMSELVES? After thinking about this even
more, I realized that the answer is yes. It goes like this:
No. 1
Traffic is going slow.
Everyone packs together and closes up the gaps.
Fast merging becomes impossible.
Incoming cars create a huge back-up.
Cars must slooooowly take turns merging.
This makes incoming traffic slow down.
Go back to the top of this loop and repeat.
This is absolutely fascinating because this self-caused situation
has a counterpart:
No. 2
Traffic flows along rapidly.
Nobody closes the gaps (they follow the 2-second rule?)
Merging is easy.
Streams of traffic flow together like a zipper.
This allows traffic to go fast.
Go back to the top of this loop and repeat.
At a merge zone, fast traffic causes traffic to remain fast, while
slow traffic causes a jam to persist. Weird! The difference between
these two situations is enormous, yet EITHER ONE can arise on the
exact same highway under the exact same amount of traffic. In the
first one, the speed might be 2 mph, while in the second one it
could be 40 mph. And here's the important part: because the situations
create themselves once they are established, sometimes they can
switch from one to the other. A smooth flow can hit a glitch and
turn into a traffic jam. Or somebody can switch them intentionally.
Suppose the traffic at a merge zone was flowing fast as in Loop
Number 2 above. Suppose I wanted to wreck everything. I could slow
way down and make all the cars pack together behind me. This would
prevent any cars in the other lane from merging into the closely-packed
lane. Cars in the merge-lane would pile up too. Then I drive off
laughing evilly, because I have just CREATED MASSIVE LONG-TERM TRAFFIC
JAM! The exit might stay jammed for hours.
Or, I could do the opposite. Suppose everything is jammed up at
the merge zone. Suppose I accumulate a huge space ahead of me and
bring it into the jam. When the huge space gets there, the other
lane of cars can suddenly change lanes, spread out, and start flowing
fast. Next, I speed up and merge with it, and so do the cars behind
me. The "zipper-like" flow has begun. The switch has flipped.
I have just ERASED a long-term bottleneck. As they say in those
old Ranier Beer ads, pretty cool, eh?
for the original article
http://amasci.com/amateur/traffic/trafexp.html
More on this subject
http://www.amasci.com/amateur/traffic/traffic1.html
