The Assassin (Sha ren zhe Tang Zhan)

This time on

"impossible engineering: Impossible railroads,"

the incredible challenges facing mountain railways...

And the remarkable engineering solutions...

They told me, "Bruno, you're crazy.

That's impossible."

that make the impossible possible.

captions paid for by discovery communications

as they make their epic journeys

across the continent,

railroads continue to push boundaries...

Inspiring engineers to find new ways

to tackle all of nature's extremes.

But there is one challenge that raises the bar

higher than any other...

The mighty peaks and sheer cliffs of mountains.

From their treacherous, winding terrain...

Semmering features grades and curves

that has never conquered before by a railroad.

To impossible inclines for trains...

The steeper you make it, the bigger the train you need in

order to overcome this incline.

And passengers to keep safe and happy.

The challenge here is, because the natural wall

is more or less vertical, so we have to find a way.

It was the challenge of one epic climb

that faced Swiss engineers in the mid 1800s.

The Swiss alps,

part of the largest mountain range in Europe

and home to some of its highest peaks.

But with their unrelentingly steep terrain,

these mighty mountains

are a railroad's most formidable opponent.

Railroad technician Steffen Reichel

is traveling on the Rigi railway

to see how adaptations to the track and the engine

made it one of the first railroads

to take on a seemingly impossible mountain climb.

Look at that sunshine.

Look at the Rigi mountain.

I love it.

And now you can hear the engine start working hard,

because it's very steep on Rigi,

and now listen to that noise.

The fireman is doing his work.

He needs to shovel 500 kilograms of coal

into the boiler up to Rigi Staffel.

Today, this train is one of the most popular

tourist trains in Switzerland, but in the early 1800s,

the only way to reach the dizzying heights

of mount Rigi was on foot or by carriage.

In 1869, engineer and locomotive builder Niklaus Riggenbach

was commissioned to connect Vitznau

on the shores of lake Lucerne

with the summit of mount Rigi 5,898 feet above sea level.

Having seen trains slipping and losing traction

on other railroads with shallower gradients,

Riggenbach knew his solution

would require radical rethinking.

The railroad would have to climb over 3,600 feet

in just over 3 miles.

Riggenbach designed a toothed rack rail

between the running rails.

A cog wheel was added to the center of the wheel axle

to mesh with this rack rail and give the train traction.

In 1871, the Rigi railway

was the first rack-and-pinion railroad in Europe

to conquer a mountain.

It's like Riggenbach built a stairway to heaven.

Taking nearly two years to complete,

Riggenbach had finally brought this mountain to the masses...

And today, as many as 500,000 people a year

make the journey to the summit.

Up here, this is one of the best views

I ever have seen in my whole life.

I have been to many mountaintops,

but none of them had that panorama as we do.

Now I know why Riggenbach conquered the mountain

with that tiny railroad,

but up here, it's only half of the problem.

Having managed to get the tourists

to the top of the mountain,

the elevated incline presented Riggenbach

with a challenge of equally tough proportions.

With a 25% gradient,

the rate of descent was creating too much stress

on the boiler and band brakes of his locomotive

as well as damaging the track.

Usually, on an incline,

most railways encountered very problem,

because the wear on the brakes was so high

that the brakes could fail,

and so you rode down without any brakes and could derail,

and many accidents happen.

For a train full of passengers,

this could've been catastrophic.

Riggenbach needed to find a way to slow the train down.

Rigi was too steep for normal braking systems,

and so he decided to use a different brake system,

a brake system which could not fall apart.

Riggenbach surmised that if the engine was

strong enough to push the locomotive

and carriages up the mountain,

then it should be strong enough to slow it down on its descent.

And now we go down by Riggenbach.

And this is what Riggenbach really invented

is the brake system.

What we hear right now is air is moving into the cylinders,

and it's pressed out by the silencer next to the stack.

Did you hear it?

The chugging noise has changed.

It is now a noise of compressed air.

When the engine is running,

the Riggenbach air valve is switched

so that exhaust will leave by the blast pipe.

To apply the brake, the throttle valve is closed

and the Riggenbach air valve

is switched in the opposite direction,

allowing the pistons to pull clean air in.

This air becomes compressed in the cylinder,

acting like a cushion and slowing the pistons down,

which, in turn, slows the train.

Personally, I think this is

the best dynamic braking system

for a steam locomotive you ever can have

because it has no additional structure or details

which need to be special.

You can build a steam locomotive of any type,

and it's an absolute reliable brake system

because it applies the brake pressure by itself.

As fast as the train goes, as harder the brake is acting.

The Rigi railway became

the highest standard-Gauge railroad in Europe.

Being here at Rigi is something very, very special

because it's the oldest operating cog rail in Europe.

It's an absolute awesome ride upwards,

and then going down, with the Riggenbach brakes,

smooth, soft.

That's the invention we are all for here.

This is what makes the genius of Riggenbach.

The Riggenbach railroad represents

just one of the many ingenious ways engineers

have overcome seemingly impossible gradients.

Given enough firepower,

most ordinary trains can climb a hill,

but cograils aren't the only way engineers have gotten creative

to solve the incline problem.

After all, extra muscle only goes so far.

Ecuador.

From the pacific ocean to the mighty Andes...

It's a country full of larger-than-life landscapes

that seemed insurmountable in the late 1800s.

The Andes mountains in Ecuador ran north-south

for about 600 kilometers with peaks over the 5,000 meters

and then actually getting down to zero level.

It was very important to connect the capital city,

Quito, and Guayaquil, the main port,

that were geographically separated.

Although only

166 miles apart as the crow flies,

these two strategically important cities

were separated by raging rivers...

Dense cloud forests, and deep ravines.

The ambition was to build a railroad across this terrain,

but as Tren Ecuador's Alex Ortiz knows,

achieving it would be no small feat.

Guayaquil, it's in the lowlands at sea level,

and Quito, it's over 2,800 meters above sea level

and then getting to the central valley.

So the engineers had this incredible task

to go from the coast through the mountains

through this steep valley.

It's very difficult to imagine a train

going through these mountains, through these vertical walls.

For centuries,

the perilous journey between the two

had only been possible by mule,

taking up to 12 days to complete.

At the end of the 19th century, the country's leadership

enlisted the help of two American brothers,

John and Archer Harman, to start work on the Transandine railway,

but there was one section that was seemingly impossible

to overcome...

The devil's nose.

With its near, precipitous drops and impenetrably hard rock face,

building a track that could circumvent

and descend this section

would pose a nearly impossible engineering challenge.

But as it turns out, the team behind this project

did not have to look far for inspiration.

When engineers needed to overcome

the impossible challenge of building a railroad

to scale the devil's nose in the Andes,

they were inspired by the trailblazers

of the region's past.

So the trails that... They are all around over here,

the ancient trails in zigzag, like a switchback,

like the ones I have on my back.

They thought this could be the great solution.

In 1908, after 10 arduous years of construction,