- 5/30/2025
This is the story of the battle to build a railway across one of the most extreme environments on Earth. To lay down over a thousand kilometres of track in a remote wilderness. To drive 7 tunnels and to raise 675 bridges all at an altitude where even a simple breath is nearly impossible to come by. 140,000 workers and 2000 medics struggled for 5 years to conquer this hostile environment to complete. the Qinghai-Tibet railway, the highest, most extreme railway in the world!
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00:00This is the story of the battle to build a railway across one of the most extreme environments on earth.
00:14To lay over a thousand kilometers of track in a remote wilderness.
00:20To drive seven tunnels through the rugged slopes.
00:25To raise 675 bridges over valleys and rivers.
00:30All at an altitude where even a simple breath is nearly impossible to come by.
00:37This is a tough place to work. Headaches, shortness of breath, freezing winds.
00:44140,000 workers and 2,000 medics struggled for five years to conquer this hostile environment.
00:53And to complete the Qinghai-Tibet Railway.
00:57The highest, most extreme railway in the world.
01:00The largest station in Asia and one of the busiest.
01:03400,000 can pass through here in a single day.
01:06Coming through with today's crowd is Finnish engineer Pasi Lautala.
01:07He's here to see for him the world.
01:08The largest station in Asia and one of the busiest.
01:09The largest station in Asia and one of the busiest.
01:10400,000 can pass through here in a single day.
01:13Coming through with today's crowd is Finnish engineer Pasi Lautala.
01:18He's here to see for himself just how one of the most extraordinary railways on the planet was built.
01:23The line to Lassa into bed.
01:24It goes so high and it goes for such a long distance over really, really rough terrains.
01:33So I don't think anything like that has been ever done on the railway engineering world.
01:45This is no ordinary rail journey.
02:00The Lassa Express is a multi-billion dollar marvel, specially built to survive at altitudes higher than the Swiss Alps and at freezing temperatures.
02:18For train-obsessed Pasi, it's a journey he's dreamed about for years.
02:28I've read about it and I've seen some of the engineering solutions they use to build the track and I gotta see it.
02:37It's 9.30 and the Lassa Express is underway.
02:45This is it. It's time to go.
02:49As director of rail transportation at Michigan Tech University, Pasi is here on business.
02:56We are doing some work connecting Alaskan Rail Network with the Canadian Rail Network.
03:01And as part of that project, we've been studying some of the cold regions railroads around the world
03:07to see how some of the other countries and some of the other regions have built them.
03:11So it's a learning experience for me.
03:13From Beijing, the Lassa Express will travel 3,000 kilometers across China to the town of Golmud.
03:23From there, the train will climb up to the Tibetan Plateau and across the roof of the world to Lassa.
03:29It's a marathon 47-hour journey, but it's the final high-altitude section of the line that interests Pasi.
03:41It crosses land higher than any mountain in the American Rockies.
03:46An environment so hostile that it's like building a railway on Mars.
03:50And it took Chinese engineers 50 years to work out how to do it.
04:00The idea to build this controversial railway dates back to the 1950s.
04:05When the Chinese army occupied Tibet in 1950, they wanted a railway to supply the troops.
04:13But to build a railway, first they needed a road.
04:18The Chinese government threw a vast labor force, equipped with basic tools against the harsh conditions of the Tibetan Plateau.
04:25But around 3,000 workers died from exposure and from altitude sickness.
04:33It was a disaster.
04:36And although the dream of a railway to Tibet lived on, the plans were eventually shelved.
04:41Today, the Lassa Express pounds its way across industrial eastern China at over 110 km per hour.
04:55It's the pride of the Chinese railways, and only the best get to work on it.
05:02Yang Jingjing is the train master.
05:05He's responsible for everything that happens on board, especially safety.
05:09I need to ensure the train has a safe journey from Beijing all the way to Lassa.
05:23He begins the day with a briefing for some of the 36 staff who look after the passengers.
05:33The 13 passenger carriages of the Lassa Express are divided into three types.
05:37Two so-called soft sleepers are the Chinese equivalent of first class.
05:42Well, this is definitely quite a luxurious way of traveling.
05:45This compartment is called the soft sleeper.
05:48There's four birds for four people, and we even have an entertainment system with some Chinese TV or movies.
05:56But it's not as luxurious for everybody in the train.
05:58Seven carriages offer hard sleeper accommodation, a bit more of a squeeze with six people to a room.
06:07And four carriages are simply fitted with seats.
06:09There are over 900 people on board who need to be fed for two days and nights.
06:22That's the responsibility of Zhang Yang and his four chefs.
06:25The most difficult part is that we have people from different ethnic backgrounds along the length of the railway.
06:36Everyone has different tastes.
06:38Tibetans, the Hui ethnic people, and other minorities all have different tastes.
06:43This makes life very difficult.
06:46And the train has plenty of hot water for those who like to make their own haute cuisine.
06:52It may look like a normal train, but later in the journey, the lives of everyone on board will depend on the hidden, high-tech features of its carriages.
07:11They've been specifically built to cope with the conditions on the Tibetan plateau.
07:16When you take a look at these trains, they look just like regular Chinese trains.
07:21There's nothing extraordinary except I see this one here.
07:24It is an oxygen outlet that you can get some extra oxygen in the high altitudes of the train.
07:35Each carriage is fitted with an oxygen-generating unit that will come into operation at high altitude.
07:42It's a small portent of what lies ahead.
07:46It's a small portent of what lies ahead of the train.
07:48It's a small portent of what lies ahead of the train.
07:49It's a small portent of what lies ahead of the train.
07:52Throughout the day, the train heads west, stopping for safety checks,
08:07and to pick up passengers.
08:10Lhasa is still 24 hours away, but already there are signs of Tibetan culture.
08:16As new passengers settle in for the night, the train is already climbing.
08:25By the time it reaches Golmud, the last stop before the Tibetan plateau, it will be 2,800 meters above sea level.
08:37By 3 a.m., most of the passengers are fast asleep.
08:41But Pasi Lautala is wide awake.
08:46This is quite an exciting moment to me.
08:48In a few minutes we are going to be reaching Golmud, which is the last station before the train climbs up to Tibet Plateau.
08:54Since I want to see how they built the track, this is the end of the line for me. It's time to get off.
09:02To find out how Chinese engineers conquered the plateau, Pasi needs to see the line close up and in daylight.
09:12It's here that the engineering challenge really begins.
09:16The remaining passengers are about to embark on a steep 2,000 meter climb.
09:25And that means an engine change to a loco with serious power.
09:31At very high altitudes, a conventional diesel can't cope with the low oxygen levels.
09:36So, bring on a pair of NJ2 Locos.
09:45138 ton diesel electric monsters with a combined output of 8,000 horsepower.
09:51Immediately behind the engine, they've added an electricity generator car.
10:01This will be the train's life support system.
10:06Supplying power, heat and most important of all, oxygen for the passengers and crew.
10:11The train is about to embark on an extreme journey that is only possible thanks to some radical engineering and a controversial political decision.
10:25By 1984, the Chinese railway system had reached Golmud.
10:34But here it stopped.
10:35For the next 16 years, the unique problems of constructing a railway at very high altitude blocked its progress to Lhasa.
10:44Then, in 1999, the Chinese government announced that it wanted to extend its railway network to the poor, undeveloped regions of Western China and into Tibet.
10:59It argued that the railway would bring prosperity to the province and raise the standard of living.
11:04Its critics claimed that the line was intended to tighten political control over Tibet.
11:12And that it would enable large numbers of Han Chinese to move here, overrunning the culture of local Tibetans.
11:21Whatever the truth, China's engineers had their work cut out to deliver on this bold plan.
11:2750 kilometers outside Golmud, Pasi Lautala begins his mission to find out how Chinese engineers solved the first challenge of this extreme terrain.
11:40To reach the plateau, they first had to cross the formidable peaks of the Kionlong Mountains.
11:47The old Tibetan highway runs close to the new railway, giving Pasi the chance to drive the route.
11:53Well, when you see these Kionlong Mountains with the snowy tops, it's no longer a surprise it took 50 years to build this railway line up here.
12:04Quite magnificent.
12:08Cars and lorries can cope with steep climbs, but heavy trains need a slow, gradual ascent.
12:14What engineers call a steady gradient.
12:16Well, they've chosen this route because this goes kind of between the mountain tops, they are following the valley between.
12:24And that's the easiest way to maintain the smooth gradient.
12:27But going straight up the valley is out of the question.
12:31The gradient is too steep.
12:33So the railway must zig-zag up it, crossing time and time again, with literally dozens of bridges.
12:40Two thirds of the way up the valley, the engineers faced an enormous challenge.
12:54Building the Sanchaha Bridge, the tallest bridge on the whole route.
12:58Right here we are crossing the river valley, so we have to maintain the railway up in the air so that we can keep the smooth gradient.
13:10It's a critical structure that had to be completed quickly so they could get supplies up to the plateau by rail to build the rest of the railway.
13:17And that meant working through the winter.
13:20By throwing an army of workers at the job, and keeping the concrete warm when temperatures plunged to minus 20, they managed to construct the bridge in just 12 months.
13:36The deadline was met.
13:37Wow! This is fantastic! I'm quite happy I got off the train.
13:48And I can't even imagine how it was to build this bridge over the winter time. Just amazing!
13:55But this was just the beginning.
13:58As Pasi heads over the Kionlong Mountains, up to the cold, thin air of the Tibetan Plateau,
14:03he's about to discover an extraordinary natural phenomenon that destroys towns.
14:15After crossing the Kionlong Mountains, day breaks for the passengers on board the T27 train from Beijing to Lhasa.
14:23It brings with it spectacular views of the Tibetan Plateau.
14:27I had a dream to come to Tibet for many years and see the scenery from the many books.
14:35And the scenery is far more better than what we imagined and from the book, actually.
14:42Yeah, so it's really great.
14:46This incredible area is so vast and cold.
14:50It's being called the Third Pole.
14:52It stretches over two and a half million square kilometers, a quarter of the area of China.
15:01Winter temperatures plunge to minus 35 degrees Celsius.
15:06And the entire area is higher than the Matterhorn.
15:12For railway engineers like Pasi Lautala, this is about as tough as it gets.
15:17If I was asked to build a railway over these mountains, I would probably run away.
15:27I don't think you can find much more of a challenge than doing something like that.
15:36Actually, you can.
15:37Because below the flat surface of the plateau lies a substance that for 50 years defeated all attempts to build a railway.
15:46Frozen Earth.
15:48Permafrost.
15:50Well, the permafrost can have depth of a few meters or all the way up to like 50 or 60 meters.
15:57And most of the permafrost stays frozen year-round.
16:00The problem is not the permanent permafrost deep in the ground, but a layer of soil and water above it.
16:08The active layer that freezes in winter and thaws in summer.
16:16In winter, the ground is frozen solid.
16:19But if I was here in the summertime, it would be like walking on a bog or a swamp.
16:23The effects of the winter freeze can easily be demonstrated.
16:28It's getting quite chilly here, so we're going to have a little experiment.
16:33I have a full bottle of water and I'm going to leave it here.
16:37We'll come back and see what's happened to it.
16:39And here's the result of our experiment.
16:47As water freezes, it expands by about 9%.
16:50Now this landscape is full of water, which behaves the same way as the water in the bottle.
16:56Over decades, the ground here can shift several meters.
17:01It's a problem that the locals have struggled with for centuries.
17:05As Pasi finds out on his first stop on the plateau.
17:11The small town of Wu Daulian, where the locals have been having a bit of a problem with their foundations.
17:19Many of the buildings in this town show damage from permafrost.
17:23Once the ground gets moving from freezing and thawing, almost nothing can stop it.
17:28As the ground rises and falls, it's pulling the town to pieces.
17:32I mean, take a look at these cracks in this building.
17:37This is a great example of what permafrost can do in the buildings.
17:41Tough for buildings, the movement of the permafrost makes it impossible to build a railway.
17:48As the builders of this line in Alaska, and these lines in Canada, found out the hard way.
17:55So Chinese engineers were expected to somehow solve the unsolvable.
18:09This nightmare problem landed on the desk of cold region scientist, Guodong Jiang.
18:18Who quickly ruled out the obvious, conventional solution.
18:21The problem with this idea is that it involves a tremendous amount of work.
18:29You have to dig out all the foundation soil, remove all the ice, and finally fill it with rocks.
18:35Over half the planned route across the Tibetan Plateau crossed permafrost.
18:42632 kilometers in all.
18:45Building deep foundations into the permafrost on such a vast scale was just too much labor, and too much cost.
18:53Even for the Chinese.
18:54Even for the Chinese.
18:57Then came a revelation.
18:59The solution had been staring Cheng in the face, right here on the plateau.
19:05The locals had figured out that the biggest problem for their houses was that the heat inside melted the ground below, causing subsidence.
19:14Their solution was to build their houses on stilts, or put pipes between the building and the ground, to allow air to float through.
19:26Cheng realized that this kept the ground below the houses frozen.
19:30It was a eureka moment.
19:34If he could keep the ground below the railway frozen, then it wouldn't subside.
19:40I think the most important issue regarding the railway is the idea that we must change from maintaining the temperature to reducing the temperature.
19:50This is essential.
19:51To try out this idea, in the 1970s Cheng's team built a research station upon the plateau at Beiljua.
20:02They built a test section of the railway embankment, and started to experiment.
20:12So here we have ventilation ducts, which are hollow pipes that run through the embankment.
20:18In the winter, they allow cold air and wind to go through the embankment, removing heat from it.
20:26Over time, something amazing happened.
20:29Year by year, the ground below got colder.
20:33Over several years, they reduced the average temperature of the ground by two to three degrees.
20:39Just enough to keep it frozen.
20:41But to build a whole railway line 600 kilometers long, with concrete tubes running through it, would still be too expensive.
20:52Cheng's cheap idea wasn't cheap enough.
20:56But he didn't give up.
20:59After years surveying the plateau, he noticed that something strange was happening beneath piles of small rocks.
21:07The reports showed the temperature under the rocks was lower than other areas.
21:13Could this point the way to an even cheaper solution than the tubes?
21:19A report from a remote part of eastern Kazakhstan confirmed his suspicions.
21:25Archaeologists had discovered ancient tombs made from piles of small rocks.
21:33They noticed that the ground away from the tombs was soft and boggy.
21:39But under each tomb, it was frozen.
21:42And had remained frozen for thousands of years, preserving the artifacts below.
21:47Somehow, these rocks were cooling the ground.
21:55Back at the research station, Cheng decided to see if an embankment built of small rocks could do the same for a railway.
22:03The purpose of these crushed rocks is to remove heat from the embankment and from the ground below.
22:09So when they are built, they make sure there is no fine material between the rocks, leaving as much space for the air to circulate as possible.
22:18Over just 14 months, Cheng's experimental rock embankment lowered the average temperature of the ground by 3 degrees Celsius.
22:28And he found out how it worked.
22:30In winter, cold, strong winds blew through the rocks, pulling heat out of the ground.
22:38While in the summer, the rocks shaded the embankment from the heat of the sun.
22:43After 50 years of frustration, Chinese scientists had stumbled onto a 2,000-year-old solution to the permafrost problem,
22:52that was about as low-tech as it gets.
22:54This can be almost a 1 meter thick layer that goes down the embankment, then down to the other side and up again, making almost like a U-shape.
23:05At last, Chinese engineers could start building the railway.
23:11In 2001, thousands of workers converged on the plateau and work began.
23:18Building the huge embankments using local materials and basic machinery.
23:29By 2002, construction crews were rolling out the railway line at an incredible pace, thanks to another very clever but simple idea.
23:39The PG-30 locomotive, which lays its own rails as it advances.
23:44As it advances, it makes building a track almost as easy as assembling a model trainset.
23:56By mid-2003, the workers had laid over 250 kilometers of track from Golmud up onto the Tibetan Plateau,
24:05and were making good progress towards Lhasa.
24:08But the battle with the permafrost was far from over.
24:13Well, in some of the areas, the permafrost is very warm, so that the rocks by themselves could not solve the problem.
24:20And in those cases, they would have to look into alternative solutions.
24:24In some sections of the route, the summer temperatures were just a little too warm.
24:32The embankments needed a little extra help to keep the ground frozen.
24:36An ingenious device was found that was once again very low-tech, harnessed nature and required no power.
24:46These bizarre-looking tubes are called thermosiphons.
24:50The idea behind these is ingenious, but really quite simple.
24:55If you have ever licked the back of your hand and blown on it, your skin feels cool.
25:03That is because the water is evaporating and that removes heat from your skin.
25:08These work in a similar manner.
25:09Up to ten metres long, with five metres buried into the ground, the thermosiphons contain ammonia, a refrigerating liquid.
25:20However, unlike a fridge, a thermosiphon doesn't need an electricity supply to work.
25:27Inside the tube, the liquid ammonia behaves a bit like the water on your skin.
25:32It absorbs heat from the ground, which causes it to boil and evaporate into a gas.
25:39The gas rises in the tube, taking the heat from the ground with it.
25:44At the top, cold wind cools the tube, and the ammonia gives up its heat to the air outside,
25:51and condenses back into a liquid, which runs to the bottom of the tube and the cycle repeats itself.
25:57Simple, low-tech genius.
25:5934 kilometres of track are cooled this way.
26:04But even thermosiphons were incapable of protecting the most vulnerable sections of permafrost.
26:12Hasi heads to an area called Qing Siu, almost a quarter of the way across the plateau,
26:20to explore the most fragile area of permafrost on the whole route.
26:24Here, the active layer of permafrost melts during the summer, and it turns into a treacherous bog that can behave almost like a quicksand.
26:37If it turns into that kind of quicksand, you can't bring anything on top of it.
26:42Everything would just sink into it immediately.
26:44The ground here gets too warm in summer, even for thermosiphons to cool.
26:50If the engineers couldn't find a way across this shifting marsh, there would be no railway.
26:56Now, engineers recognised that at most difficult locations, crushed rocks and thermosiphons were not enough to have long-lasting railway.
27:06So they decided to build structures or dry bridges at these locations.
27:11Now, this was more expensive, but they believed it was the right way to go.
27:15The answer, they believed, was to treat the bog as if it was water and build bridges.
27:24Along the route, teams of workers drilled thousands of holes deep into the permafrost.
27:30By drilling through the active layer and down into the ice below that stayed frozen year-round, they could build on solid foundations.
27:38At least, that was the theory.
27:42Because they now faced a new nightmare.
27:46And again, it was all about temperature.
27:49The concrete poured into the ground to make the piers of the bridges could destroy the very foundations they were building on.
27:57When you mix the concrete, it goes through a chemical reaction.
28:02As it sets, it gives out heat.
28:07In this experiment, the temperature of the mix steadily increases.
28:13When all your work is aimed at keeping the permafrost frozen, heat is the last thing you want.
28:20The temperature here is 13 degrees.
28:23That would be enough to melt the ice around the structure and to make it unstable.
28:28So how would Chinese DIY engineering deal with this one?
28:33By putting Mother Nature to work for them.
28:37They would build in the dead of winter, when ambient temperatures fall below freezing.
28:43And cool the concrete to 5 degrees, pouring it as quickly as possible before it sets.
28:48By bringing in thousands of workers, they built nearly 3,000 bridge piers in just 7 months.
29:00A breathtaking achievement, epitomized by one of the iconic features of the line.
29:06The spectacular 11.7 kilometers long Ching Sua Bridge.
29:11The longest permafrost bridge in the world.
29:13The permafrost problem was finally conquered.
29:18In all, over 160 kilometers of the Qinghai-Tibet Railway is built on bridges like this.
29:26One-seventh of the whole route.
29:29But permafrost was not the only formidable natural challenge of the plateau.
29:34The terrain is so high that it is deficient in one of the basic ingredients for life.
29:41Up here, you battle to stay alive.
29:45With an average altitude of 4,500 meters, the Tibetan plateau is unsurprisingly very sparsely populated.
29:54About a third of the way across the plateau, the Tibetan town of Tuotoa has a population of 1,300.
30:04The locals have adapted to living at high altitude over hundreds of years.
30:09But for anyone else, it's a serious hazard.
30:13Up here, breathing is much harder than at sea level.
30:17Despite that handicap, Pasi is taking on the local pool champion to demonstrate.
30:25Air is mainly made up of molecules of nitrogen and oxygen.
30:31About one in five molecules is oxygen.
30:34At sea level, there are plenty of molecules of both nitrogen and oxygen in every breath we take.
30:40But the higher you go, those molecules get fewer and fewer.
30:49At 4,700 meters, where I am now, the amount of oxygen in the air is almost half of that at the sea level.
30:57Here, the body finds it very hard to get enough oxygen out of the air, into the blood and to the muscles where it's needed.
31:05The harder we work, the more oxygen our bodies need.
31:10And if we don't get enough, it can be fatal.
31:14In severe cases, fluids can leak into your lungs and brain and kill you.
31:24As the Lasser Express travels over the plateau, one of the most important jobs for the crew is to keep an eye on the passengers.
31:31They are looking for signs of altitude sickness.
31:35The train is now traveling at 4,500 meters above sea level.
31:41Medical advice recommends you should take five days to climb to this altitude, to allow time to acclimatize.
31:48The train has done it in just 32 hours.
31:52At this altitude, around three quarters of people start to experience altitude sickness.
32:00I can feel that the air is very thin.
32:03When I was taking pictures, even slight movements made me feel breathless.
32:06Since Chuna River, I've started to feel dizzy and sick.
32:16My nose feels very dry and so does my child's.
32:20He has also complained of tummy ache.
32:22To reduce these symptoms, remember those special oxygen generators.
32:29They fill the carriages with enriched air.
32:32The oxygen generators inside each carriage use a technique called membrane separation.
32:38Air from outside the train is compressed and pumped through small tubes.
32:42The walls of those tubes are made of a membrane containing small holes, which allow more of the smaller oxygen molecules to pass than the larger nitrogen.
32:54The unwanted nitrogen is exhausted from the train via an outlet pipe.
32:59While the oxygen enriched air is fed into the carriages.
33:03It raises the level in the air from 21% to 24%.
33:10It's not much, but it makes most people feel better.
33:14But for people who are really suffering, there is a backup system.
33:19The staff give afflicted passengers a tube, which they can plug directly into a supply of 40% oxygen.
33:27Every berth and seat on the train has its own oxygen supply.
33:31The train is not pressurised like an aircraft cabin.
33:43But the doors are sealed to keep the oxygen enriched atmosphere inside.
33:49And there is a very slight positive pressure, so the air outside can't seep in.
33:53By comparison, for the workers who built the track, conditions on the plateau were a living hell.
34:05Hard physical labour at this altitude is not only difficult, it's dangerous.
34:11I really feel quite fragile up here at the plateau.
34:20I have a bit of a headache, and even though I'm walking at less than regular pace, I'm completely out of breath.
34:26Many of the 3,000 workers who died building the first road into Tibet in the 1950s died from altitude sickness.
34:38And the railway engineers were keen not to repeat the disaster.
34:41But they needed extreme structures to be built at extreme altitudes, including one in particular.
34:52I just had to see this. This is the highest railway tunnel in the world.
34:56At 4,905 metres above sea level, the Chinese called the Funguo Shan Tunnel the nearest door to heaven.
35:07I can't even imagine what people who built this had to go through.
35:12We are at the 4,900 metres, and there's not a lot of oxygen, so it had to be literally a headache to build it.
35:19Building this tunnel required hundreds of labourers to live and work at this extreme altitude.
35:32So the railway company brought in one of China's leading experts on high-altitude medicine.
35:38Professor Tianyi Wu, head of the Qinghai Highland Medical and Scientific Research Centre.
35:44His mission was to help the engineers build the tunnel and other high-altitude structures without the tragic loss of life of the 1950s road construction.
35:57During the initial building of the Tibetan Railway, as most of the workers were from regions around sea level, they were not adapted to the highlands.
36:09Aware of the dangers of rapid ascent, Professor Wu prepared a careful plan.
36:19Our first measure was a step-wise adaptation, which meant letting them ascend gradually.
36:27So from inland, after the journey from Beijing to Xining, they'd stop for three days, and then a week's stop at Golmud, then ascend to the Tangula Mountains.
36:38Professor Wu was supported by a vast team of 2,000 doctors and nurses.
36:47Infirmaries were built every 18 kilometres along the route to treat sick workers.
36:54And Professor Wu made sure there was a good supply of oxygen.
36:57During the process of building the railway, there were 21 oxygen-making stations built, averaging about one for every 50 kilometres.
37:11This would ensure that during the work, every worker had a small oxygen supply device.
37:16But the heavy cylinders made the work harder.
37:24So instead, oxygen generators were set up to pump oxygen-enriched air through the tunnel to the workers at the face.
37:33With the extra oxygen, it was as if they were working 1,200 metres closer to sea level.
37:44But many of the tunnel workers still got sick.
37:48So Wu's team installed 25 emergency hyperbaric oxygen chambers along the route of the line.
37:54Over time, the workers adapted to the altitude.
38:01By the fifth year, the incidence of high-altitude illness was very low.
38:07And there was not a single case of serious high-altitude illness.
38:11By October 2002, the workers had completed the Fengwoshan tunnel.
38:18It was a major triumph.
38:20It opened the way to the rest of the plateau and the route south to Lhasa.
38:25But it wasn't fast enough for the Chinese government.
38:31In 2004, Beijing announced that it wanted the railway completed by early 2006, a whole year ahead of schedule.
38:39It was an almost impossible demand on an already ambitious programme.
38:46There was only one way they could pull it off.
38:50They decided to leap ahead to the town of Amdo in Tibet,
38:54and start building the railway from there in two directions at the same time.
38:59One machine would lay track back towards Golmud,
39:03while a second machine would build onwards towards Lhasa.
39:07It would triple the speed of construction.
39:11By the summer, three teams of track players were blazing their way across the plateau.
39:16In total, 140,000 workers worked on the high-altitude section of the line.
39:27Thanks to the medical plan, they avoided the fate of the workers of the 1950s who built the original road.
39:33So despite having over a thousand cases of severe high-altitude illness over the five years, no one died.
39:43The mortality rate was zero.
39:45Thanks to the onboard oxygen supply, the crew and passengers on the Lhasa Express are travelling in relative safety.
40:00But as they cross the plateau, their lives depend on another critical safety system.
40:11To save money, the line was built as a single track.
40:16But that brings with it a constant danger.
40:18If two trains travelling in opposite directions are accidentally routed onto the same line, there could be a head-on collision.
40:27But to control the trains, there are no signals.
40:31Instead, alongside the track, every 15 or so kilometres, there's a mobile phone antenna
40:37that passes information between the train and the control centre, 2,300 kilometres away.
40:46Along the route, there are crossing loops, short sections of double-track where trains can pass each other.
40:5339 hours into its journey, the Lhasa Express is approaching one of these passing points.
41:00Tangula, the highest railway station in the world.
41:04It's a ghostly place.
41:07The station is simply a passing point for trains.
41:10It's early afternoon, and the train is still 500 kilometres from Lhasa.
41:18Inside, the passengers are protected from the extreme environment outside.
41:23But while the train protects the passengers from the environment, it must also do the reverse.
41:30It has to protect the fragile ecosystem of this ancient landscape from human pollution.
41:35The Tibetan Plateau contains the Kakashili and Sangjing Nguyen Nature Reserve, the second largest nature reserve in the world.
41:50It's larger than England and Wales combined.
41:54It's a delicate ecosystem that could be easily disrupted and destroyed.
41:59On most trains around the world, sewage and wastewater are dumped straight onto the track.
42:07But not here.
42:09The heat from all that water would warm the permafrost and degraded.
42:14It would destroy the very foundations the train runs on.
42:18So the Chinese have gone green.
42:21Instead of dumping wastewater on the track, the Lhasa Express stores it in collection tanks below each carriage.
42:30Each tank holds 500 litres of wastewater, enough for 250 toilet flushes.
42:38Every night, at Golnud Station, a small fleet of mini-tankers drives along one of the platforms.
42:47At 11.45pm, the Lhasa Express's sister train, the T-28 from Lhasa, pulls in on its way to Beijing.
42:59After crossing the plateau, the train's tanks are full of wastewater.
43:03A small army of workers leaps into action.
43:09They attach hoses to the tanks and pump the wastewater out.
43:14The whole operation takes less than 10 minutes.
43:17As the train leaves the station, the tankers head off to dispose of the waste safely.
43:25And 900 relieved passengers head off to Beijing.
43:30Pasi is impressed by the efforts to conserve this fragile ecosystem.
43:43But in his trip across the plateau, he's discovered that all is not quite right with the railway.
43:48The line itself is still under threat.
43:55Despite all the efforts to keep the ground beneath the line frozen, the Qinghai-Tibet Railway is being attacked by an unexpected enemy.
44:04In parts of the plateau lies a natural phenomenon that has been here for thousands of years.
44:10Sand.
44:13Now this is quite impressive.
44:15I didn't really expect to see sand dunes up here in the plateau.
44:19It's almost like being at the beach.
44:21The problem with sand is that unlike mud, its grains don't stick together.
44:28If I stick my hand in here on a windy day like this, it just blows away.
44:34And it's blowing straight towards the railway embankment, half a kilometre away.
44:38And this is where the problem comes.
44:41The sand that has been blowing in the wind is filling up the gaps in the rock embankment.
44:47As the crushed rock embankment fills up with sand, it loses its ability to cool the ground below.
44:55In time, this could lead to the permafrost thawing out, buckling the track.
45:01So the railway company is trying its best to stop this happening.
45:05They have erected dozens of these fences to keep the sand away from the tracks.
45:12You can see how the sand has piled up behind the fence.
45:15As the wind blows through the fine mesh of the fences, it slows down and drops the sand.
45:24But despite all their efforts, the sand here has already permeated the rock embankment.
45:29The sand only affects a small section of the line, but there's another much more serious threat to the long-term future of the railway.
45:40And this one is man-made.
45:42The permafrost on the plateau is extremely sensitive to changes in temperature.
45:49And global warming is slowly heating it up.
45:53Our country has done research in this field and has given us a set of data speculating that the temperature of the Qinghai Tibetan Plateau will rise by 2.2 to 2.6 degrees Celsius over the next 50 years.
46:08The railway is designed to cope with a 3 degree increase in average temperature.
46:15But other factors could raise the temperature far more than this.
46:20Across the continent, and particularly in neighbouring India, coal is used extensively in fires and furnaces that produce smoke containing black particles of sod.
46:32Much of that sod falls onto the snow that covers the Tibetan Plateau in winter.
46:39The dark particles cause the dirty snow to absorb more of the sun's heat than clean snow.
46:46In spring, the snow now melts earlier than before, adding to the warming of the plateau.
46:52Despite all the measures to keep the rail bed frozen, if the temperature rises more than 3 degrees, the railway could be in trouble.
47:06The Lhasa Express sweeps over the stunning Triple Span Bridge across the sacred Skyatu River.
47:16For the crew of the train, it's a welcome sight.
47:19After 47 hours, it's a sign they are nearing their journey's end.
47:23And this is it. The vast new Lhasa station.
47:29At 35 million dollars, it's a symbol of the Chinese determination that the railway is here to stay.
47:36With this line, Chinese engineers have proved they are among the best in the world.
47:42And they've laid the foundations for an expansion programme the like of which the world has never seen.
47:48In the next five years, China will spend an estimated 300 billion dollars constructing over 30,000 kilometres of new railways.
48:05For Pasi Lautala, his time on the plateau has come to an end.
48:09Coming up here has been a stunning experience for me.
48:12I already had a lot of respect for people who built this railway, but only now I truly realise the challenges they faced.
48:21I mean, this is a tough place to work. Headaches, shortness of breath, freezing winds.
48:27Not only they got the railway built, but from an engineering point of view, it really is quite amazing.
48:33The Qinghai-Tibet Railway is a truly monumental engineering achievement.
48:40A vast labour of human endeavour and ingenious low-tech engineering that shows the way forward for new railway lines all over the world.
48:49Perhaps the start of a new golden age of railways.
48:53The Qinghai-Tibet Railway.
48:54The Qinghai-Tibet Railway.
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