The Assassin (Sha ren zhe Tang Zhan)

This time on "Impossible engineering,"

extreme railroads.

Railroads of the water world.

Their unique challenges...

The majority of the surrounding area is swamp and bayou.

You really can't even see land on the other side.

And the ingenious solutions...

So this is it.

That's the solution the engineers found.

It's an incredible effort to do that.

Undoubtedly, this is the most challenging

engineering project ever to have been realized.

That make the impossible...

Possible.

It's difficult to imagine life before the railroads

when vast expanses of terrain

left some lands laying undiscovered.

Since the 19th century, engineers have taken on

some of the planet's harshest landscapes...

Building railroads to cross countries

and connect remote communities.

But there's one environment

that presents an almost impossible challenge.

Engineers have fought their hardest battles

to overcoming our water worlds.

Just have a look around.

Incredible terrain here. So many challenges.

The atmosphere is really moist and really salty.

Corrosion in certain areas is absolutely massive.

The difference of level... about 70 meters.

It needed some very special engineering process

to solve the problem.

And at the end of the 19th century,

it was one giant stretch of water in the U.S.

That would prove profoundly challenging for engineers.

Louisiana... it's a region that's characterized

by its wet, swampy geography.

In the late 1800s, engineers were challenged

to build a railway that could connect New York

and San Francisco with the trading port of New Orleans.

However, an imposing body of water stood in their way...

Lake Pontchartrain.

Today's a beautiful day, and the seas are flat calm,

but, uh, I've been out here with winds

over 50 miles per hour

and seas in excess of 8 feet.

Railroad engineer pat Weldon

has experienced the challenges of the lake firsthand.

The majority of the surrounding area

is swamp and bayou.

You know, you'll look across lake Pontchartrain,

and you really can't even see land on the other side.

To conquer this formidable body of water by train

requires a work of engineering on an equally grand scale.

The lake Pontchartrain trestle.

Stretching 5.8 miles long.

This super-sized concrete ballast deck bridge

is the longest railway crossing over water on the planet.

Originally built entirely from wood,

this record-breaking structure

was completed over 130 years ago.

Still standing strong against the elements today,

pat's making his way out on the water

to carry out some critical repairs

while his team is riding the rails

in a specially adapted truck.

All right. Here we go. Mr. Dave, are you ready?

All clear.

Overcoming the massive distance across the swampy lake,

the trestle grants the railroad direct access into New Orleans.

When you grasp the concept that we're covering

over 5 1/2 miles of lake with a bridge,

it's just an incredible feat.

And maintaining this link is vital.

Yeah, we'll start on the joints first

and get that knocked out.

While splitting the lake from shore to shore

solved the challenge for the railroad,

it creates another problem for boats.

Your vertical clearance

for the majority of the bridge is very low.

Most boats, even moderate-sized...

It will be difficult for them to pass

underneath the ballast deck.

Unloading station here.

To allow both water and train traffic

to travel the lake without issue,

the Norfolk Southern railroad

turned to an ingenious engineering solution.

Spanning 219 feet,

this remarkable piece of railroad infrastructure

is the key to the Pontchartrain trestle's success.

The brainchild of American engineer

William Donald Scherzer.

The rolling bascule is renowned

for its robust, low-maintenance design,

ideal for operating in the watery wilds of the lake.

This is a tough place to get into.

To make repairs is a difficult thing to do.

There's no other place on Norfolk Southern

or any other railroad, for that matter,

that really compares.

To get today's track maintenance work done,

the bascule's impressive engineering

needs to kick into gear.

We have machinery at the top of the bridge

that is powered by two electric drive motors.

There are two pinions,

and those pinions rotate across a rack system.

Essentially, what happens is it applies force

to open the bridge.

By harnessing the nearly 830-ton mass

of the counterweight

to assist the motors in lifting the span,

the bridge rolls back like a giant rocking horse.

This rolling action allows for

a much smoother transfer of load while the bridge operates.

With railroad operations now at a standstill,

the team needs to work fast.

How's it look, Jeb?

We had this... Uh, 2:00 P.M. looks good.

Good deal. Sounds good.

Facilitating the crossing

of up to 15 freight trains a day,

the bridge's heavy use results in wear and tear

to some of its key components.

For example, the miter rails.

These miter rails act as running rails for our train traffic.

They also allow the drawbridge to operate up and down

and for those rails to break

when the drawbridge is operated to the raised position.

Miter rails are composed

of two interconnecting pieces of track.

When the span opens,

the lift rail slides away from the stationary rail.

And when the bridge closes,

the two realign with millimeter precision.

Anytime that we have

a major crack or defect in the rail,

it either has to be repaired or it has to be slow ordered.

And a slow order is basically

a speed restriction that requires us

to reduce the operating speed of the train.

Today's repairs are critical, yet straightforward,

but this bridge has had to withstand

more than simple wear and tear in its lifetime.

The exposed location leaves it vulnerable

to the very worst weather that nature can muster.

This rail line is a vital link

to our gateway in New Orleans, Louisiana.

If a storm was to damage

or destroy any portion of this bridge,

it would have a serious impact on our operations.

It's a nightmare scenario

that the railroad experienced in 2005

as the southeast was ravaged by one of the worst storms

in American history... Hurricane Katrina.

The Pontchartrain railway bridge

actually lost 4.7 miles of its track and ballast section.

That track was washed off the bridge deck

and into the bottom of the lake.

Despite the unprecedented destruction

wrought by Katrina,

the railroad's maintenance teams fought back.

We used a total of nine barge-mounted cranes,

and we had a team of divers that worked with the cranes

to attach rigging to the track

and then pull it up and back onto the bridge deck.

16 days after the landfall

of one of the worst hurricanes in modern history,

Norfolk Southern was able to restore rail service

into New Orleans.

The amount of determination was nothing short of remarkable.

Since restoring service across the lake

in the wake of Katrina...

We get this bridge to the upright position.

You guys planning on taking it back down?

Yes, sir. That's correct.

I told them to bring it right back down.

Okay. Understood.

The Pontchartrain trestle

has continued to act as a vital link into New Orleans,

and today's repairs are keeping this railroad on track.

This is northbound train 198.

Every day, this record-breaking bridge

continues to allow the railroad

to conquer this vast body of water

and achieve the seemingly impossible.

This is an amazing engineering feat,

the construction of this bridge.

And to be able to be part of that and have some hand

in maintaining the safe operation of the railroad

is very gratifying.

While railroad engineers

strive to overcome our water worlds,

some of the most remarkable achievements

have been realized underwater.

The English channel,

stretching as wide as 150 miles across.

It's the dividing line that separates Great Britain