What is phantom traffic and why is it ruining your life?
-
0:07 - 0:09You’re cruising down the highway
when all of a sudden -
0:09 - 0:12endless rows of brake lights appear ahead.
-
0:12 - 0:15There’s no accident, no stoplight,
-
0:15 - 0:18no change in speed limit
or narrowing of the road. -
0:18 - 0:21So why the @#$%! is there
so much traffic? -
0:21 - 0:25When traffic comes to a near standstill
for no apparent reason, -
0:25 - 0:28it’s called a phantom traffic jam.
-
0:28 - 0:30A phantom traffic jam
is an emergent phenomenon -
0:30 - 0:35whose behavior takes on a life of its own,
greater than the sum of its parts. -
0:35 - 0:39But in spite of this,
we can actually model these jams, -
0:39 - 0:41even understand the principles
that shape them— -
0:41 - 0:43and we’re closer than you might think
-
0:43 - 0:46to preventing this kind of traffic
in the future. -
0:46 - 0:51For a phantom traffic jam to form,
there must be a lot of cars on the road. -
0:51 - 0:54That doesn’t mean
there are necessarily too many cars -
0:54 - 0:57to pass through a stretch
of roadway smoothly, -
0:57 - 1:01at least not if every driver maintains
the same consistent speed and spacing -
1:01 - 1:03from other drivers.
-
1:03 - 1:05In this dense, but flowing, traffic,
-
1:05 - 1:09it only takes a minor disturbance
to set off the chain of events -
1:09 - 1:12that causes a traffic jam.
-
1:12 - 1:14Say one driver brakes slightly.
-
1:14 - 1:18Each successive driver then brakes
a little more strongly, -
1:18 - 1:22creating a wave of brake lights
that propagates backward -
1:22 - 1:24through the cars on the road.
-
1:24 - 1:29These stop-and-go waves
can travel along a highway for miles. -
1:29 - 1:31With a low density of cars on the road,
-
1:31 - 1:34traffic flows smoothly
because small disturbances, -
1:34 - 1:38like individual cars changing lanes
or slowing down at a curve, -
1:38 - 1:41are absorbed by other
drivers’ adjustments. -
1:41 - 1:46But once the number of cars
on the road exceeds a critical density, -
1:46 - 1:50generally when cars are spaced
less than 35 meters apart, -
1:50 - 1:53the system’s behavior
changes dramatically. -
1:53 - 2:00It begins to display dynamic instability,
meaning small disturbances are amplified. -
2:00 - 2:04Dynamic instability isn’t unique
to phantom traffic jams— -
2:04 - 2:10it’s also responsible for raindrops,
sand dunes, cloud patterns, and more. -
2:10 - 2:13The instability is
a positive feedback loop. -
2:13 - 2:15Above the critical density,
-
2:15 - 2:19any additional vehicle reduces
the number of cars per second -
2:19 - 2:22passing through a given point on the road.
-
2:22 - 2:26This in turn means it takes longer
for a local pileup -
2:26 - 2:31to move out of a section of the road,
increasing vehicle density even more, -
2:31 - 2:35which eventually adds up
to stop-and-go traffic. -
2:35 - 2:40Drivers tend not to realize they need
to break far in advance of a traffic jam, -
2:40 - 2:44which means they end up having
to brake harder to avoid a collision. -
2:44 - 2:49This strengthens the wave of braking
from vehicle to vehicle. -
2:49 - 2:53What’s more, drivers tend to accelerate
too rapidly out of a slowdown, -
2:53 - 2:55meaning they try to drive faster
-
2:55 - 2:58than the average flow of traffic
downstream of them. -
2:58 - 3:03Then, they have to brake again,
eventually producing another feedback loop -
3:03 - 3:06that causes more stop-and-go traffic.
-
3:06 - 3:09In both cases, drivers make traffic worse
-
3:09 - 3:13simply because they don’t have a good
sense of the conditions ahead of them. -
3:13 - 3:18Self driving cars equipped with data
on traffic conditions ahead -
3:18 - 3:21from connected vehicles
or roadway sensors -
3:21 - 3:25might be able to counteract
phantom traffic in real-time. -
3:25 - 3:29These vehicles would maintain
a uniform speed, safety permitting, -
3:29 - 3:33that matches the average speed
of the overall flow, -
3:33 - 3:35preventing traffic waves from forming.
-
3:35 - 3:38In situations where there’s
already a traffic wave, -
3:38 - 3:42the automated vehicle
would be able to anticipate it, -
3:42 - 3:45braking sooner and more gradually
than a human driver -
3:45 - 3:48and reducing the strength of the wave.
-
3:48 - 3:51And it wouldn’t take that many
self-driving cars— -
3:51 - 3:57In a recent experiment, one autonomous
vehicle for every 20 human drivers -
3:57 - 4:00was enough to dampen
and prevent traffic waves. -
4:00 - 4:03Traffic jams are not only
a daily annoyance– -
4:03 - 4:05they’re a major cause of fatalities,
-
4:05 - 4:09wasted resources,
and planet-threatening pollution. -
4:09 - 4:12But new technology may help reduce
these patterns, -
4:12 - 4:14rendering our roads safer,
-
4:14 - 4:18our daily commutes more efficient,
and our air cleaner. -
4:18 - 4:20And the next time you’re stuck in traffic,
-
4:20 - 4:25it may help to remember that other drivers
aren’t necessarily driving spitefully, -
4:25 - 4:30but are simply unaware of road
conditions ahead— and drive accordingly.
- Title:
- What is phantom traffic and why is it ruining your life?
- Speaker:
- Benjamin Seibold
- Description:
-
View full lesson: https://ed.ted.com/lessons/what-is-phantom-traffic-and-why-is-it-ruining-your-life-benjamin-seibold
You're cruising down the highway when all of a sudden endless rows of brake lights appear ahead. There's no accident, no stoplight, no change in speed limit, or narrowing of the road. So why is there so much traffic? It's due to a phenomenon called a phantom traffic jam. Benjamin Seibold explains why it happens and how we might prevent it in the future.
Lesson by Benjamin Seibold, directed by Cris Wiegandt.
- Video Language:
- English
- Team:
- closed TED
- Project:
- TED-Ed
- Duration:
- 04:31
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Tara Ahmadinejad edited English subtitles for What is phantom traffic and why is it ruining your life? |