Today on What If,
we're going to build
the highest bridge on planet Earth.
Welcome to the Qinghai-Tibet Plateau,
the “Roof of the World.”
It’s home to the world’s
tallest mountain, Mount Everest.
But also the longest,
deepest canyon on the planet,
the Yarlung Zangbo Grand Canyon.
This super canyon
is 505 km (313 mi) long
and 6 km (3.7 mi) deep.
And it’s here
that we’ll be taking on
one of the most
epic engineering challenges ever.
Building a bridge so high
it could take your breath away,
literally.
For inspiration,
let’s look at how our project
would compare
to the world’s current tallest bridge,
China’s Beipanjiang bridge.
This huge, concrete cable-stayed structure
carries people 1,341 m (4,400 ft)
across the Beipan River.
But even at a dizzying height
of 565 m (1,854 ft) above the river,
it would find itself
in a very distant second place.
Our bridge would be
over 10 times higher.
So let’s get started.
Standing face-to-face
with the deepest canyon in the world,
you’d be so high
above the rivers below you
that you could stack seven of the world’s
tallest skyscraper,
the Burj Khalifa, on top of each other.
Or the entirety of Mt. Kilimanjaro.
But the air you’d be breathing
would have less than half
of the oxygen available at sea level.
While working on this
gravity-defying bridge,
you could suffer from high-altitude illness.
This would make breathing difficult,
cause headaches
and make you feel light-headed.
You and your crew
should carry oxygen to be safe.
If you got dizzy and fell,
you’d drop straight through several
different ecosystems.
From snowy mountain peaks
to temperate coniferous forests
to sub-tropical rainforests.
All in 35 seconds.
Adding to your already
full plate of design challenges,
you’d be surrounded
by tall, dangerous mountain peaks.
And your job would be to connect
two of these mountains,
Namcha Barwa
and Gyala.
They stand a staggering
22 km (13 mi) apart.
This would mean that
not only would our bridge
be 10 times higher
than the Beipanjiang,
it would also be about 16 times longer.
But just like that one,
cable-stayed suspension
would be the best design option.
All you'd need
would be massive cables
of tightly-braided steel wires.
They'd rest on top of towers
anchored to either side of the bridge.
A suspension bridge like this
would also be the best way to go
because it would be better
at withstanding earthquakes.
And the Tibetan Plateau
is a region that is highly prone
to earthquakes.
But that wouldn’t be
the only force of nature
you’d have to concern yourself with.
You’d also face severe weather.
Your crew
would need to deal with fog,
rain and freezing temperatures.
And then there's the wind.
Your design
would require the bridge
to be as light and as flexible as possible.
But you’d need to make sure
it remains stable,
even in the most extreme winds.
One solution would be to build
pendulum-like devices
onto each tower
to balance any swaying.
Or you could construct a stabilizer fin
beneath the center of the roadway
that would
keep movement to a minimum.
But enough about the ways
weather could affect our bridge.
What about the ways
our bridge could affect the weather?
All of this uber-engineering
would be underway in a region
that is a diverse habitat
for many plants and animals.
One of the factors in this
is the steep V-shape of the canyon.
It helps funnel warm, moist air
north from the Indian Ocean
up to the plateau.
Our bridge would need
an entire infrastructure
to meet construction demands.
Your crew would start by building roads
that climb up the mountains.
And then, working from both sides
at the same time
like during the construction
of California's Golden Gate Bridge,
you’d bring them together
in the center.
All this could definitely impact
the very important flow of air
in the region.
And you’d need to make sure
that the construction process
doesn’t destroy the habitats of wildlife
like the Bangladesh tiger,
the bear monkey
or the giant boa constrictor.
Would it be worth it?
And is there any way to calculate
the final price tag
for a project so huge
and with so many challenges?
Well, given that this is
16 times bigger than the Beipanjiang,
it could cost upward of $2 billion,
at the very least.
But that would be pretty cheap
compared to an even more
daring feat of engineering,
a highway in space.
But that’s a story for another WHAT IF.