- It's not rush hour, (light classical music)
there's no construction, no accident,
but, boom... (record scratches)
traffic jam, (hard rock music)
seemingly out of nowhere.
Why? (horn honking)
Researchers call this a phantom traffic jam,
but it's not supernatural; it's mostly caused by humans.
- [Researcher] These are jams that occur
even without the presence of an accident,
without the presence of, say, an on ramp,
so no seeming cause.
- [Narrator] Here's how they happen.
- [Researcher] When vehicles are bunched up
too closely together,
then a small tap on the brake pedal
of one car at any point in time
could cause a of driver behind it
to also tap on its brake pedal a little bit.
- [Narrator] This continues down the line of cars,
each one pressing the brakes just a little more.
- Until there's a car that actually has to come
to a complete stop,
and then all the vehicles behind it also have to stop,
and then we have this formation of a traffic jam
that may have just started from this little,
little tap on the brake pedal.
- [Narrator] This is different than just regular congestion.
Although they do happen during heavy traffic,
these phantom traffic jams
are actually super energy inefficient
and more dangerous than typical congestion.
- Phantom jams are bad because they force drivers
to drive, stop, drive, stop,
and that's where all the energy inefficiency comes,
'cause every time you stop, you have to re-accelerate,
and that's how you burn fuel.
- When a vehicle is coasting or decelerating,
it's emitting much less than if it's blasting the engine.
- But there's a secondary impact of phantom jams,
and that's the fact that they increase the likelihood
of accidents.
- [Narrator] So if phantom traffic jams
are mostly created by humans,
could the solution be non-human drivers?
No, not that kind. (record scratches)
This kind: self-driving cars,
also known as automated vehicles.
Could they actually eliminate some traffic jams
and make the roads safer?
- On average, if a driver stops and drives
and stops and drives,
the travel time would have been exactly the same
if the person had driven
at the average speed the whole time,
and so that's one of the things
that traffic flow smoothing is trying to achieve.
- In the case of automated vehicles,
I would say we actually have this additional opportunity
that, while we're helping passengers
get to their destination,
we can do a few other things along the way:
we can help smooth out traffic;
we can help to make the roadways safer;
we can help to make the roadways more energy efficient;
reduce air pollution.
- [Narrator] Experts say that having
all autonomous cars on the road
would be the best way to keep traffic moving smoothly,
but can self-driving cars prevent phantom traffic jams
if they're sharing the road with humans?
- So, in the case of phantom jams,
the intention of the human
is usually to catch up with the car in the front,
which is something relatively easy to model for a machine,
and which is also something relatively easy
for a machine to counteract.
- [Narrator] So to counteract the start of a phantom jam,
the autonomous cars would figure out
the best following distance and speed
to avoid making any instability in traffic worse.
But on the road, humans, aren't always predictable
or, let's be honest, paying attention,
at least not compared to other autonomous cars.
- Humans are complex,
and also the variety of goals they have
when they go on the freeway is quite wide.
In some ways, automation is easier
when the human is taken out of the equation.
- [Narrator] Would a robot slow down
to look at an accident on the highway?
Probably not.
And a human's main goal
probably isn't to prevent a phantom traffic jam,
even if that human is a professor
who studies the dynamics of transportation systems.
- I'm definitely a person who,
if I see a lane that's open, I go there,
and I move in and out of traffic,
and so that can actually be optimal sometimes.
- [Narrator] Though the definition of optimal
may vary between drivers, and between human and machine.
- There's a notion of being socially optimal
versus optimal for yourself.
This is the benefit, I think, of autonomous vehicles,
is that, if you can look a little bit beyond yourself,
cars are doing things that are optimal
for the global system, as opposed to a local system.
- [Narrator] So for researchers like Cathy Wu,
the goal is for the automated cars
to be safer, better drivers than humans,
not replicate human driving.
- If we wanna do better,
we as humans should not be telling the automated systems
what to do, or it will just reflect back
all of our imperfections
that we can directly specify this objective.
And what was remarkable for us to find
is that the system could actually identify strategies
that were effective in achieving some of these objectives
that are different than how humans drive.
- [Narrator] Researchers are still testing
traffic control technology in autonomous cars.
And there are still a number of barriers
to accessing these kinds of vehicles.
- The aspect of cost and access
is something that concerns me.
I don't have an answer.
I think that what we'll see, early on at least,
is automated technologies in more niche scenarios.
We'll see them probably in automated trucking for freight,
in low-speed environments like college campuses,
in fair weather locations, like Arizona, like California,
in shuttle buses on fixed routes.
And so, in these restricted domains
this is still rather narrow,
but this, I think, will allow the designers and engineers
to test out the technology, adjust for risk,
gradually build consumer acceptance and trust.
- One of the things I like to tell people
about autonomous vehicles
is that it's perfect if we can get it right,
but we should also understand the things that arise
that we as a society need to come to
before we release them all on the road.
(light electronic music)