These megaprojects will cost close to half a trillion dollars by the time they are complete.

The most expensive project on our list today doesn’t hold a candle to the most expensive construction project in history. It’s not the Pyramids of Giza, nor is it the Great Wall of China.

It may surprise you to learn that it is, in fact, the interstate highway system project beginning in 1955 in the U.S. that takes the cake. It connects over 47,000 miles of highway crisscrossing the continental U.S. This 35-year project cost a whopping $459 billion.

Although this outshines the value of these current projects, today’s biggest construction marvels employ far more impressive technology and techniques during construction than the construction feats of old.

What is Considered a Megaproject?
A megaproject has three distinct characteristics:
– Substantial Capital Investment
– Deep Logistical Complexity
– Long-Term Effect on Economy

Take a look at these modern megaprojects.

Hong Kong-Zhuhai-Macao Bridge
$10.6 billion

This bridge, when complete, will link a man-made island near Hong Kong with another artificial island near the eastern shore of Macao—over 34 miles. Although it’s technically a collection of bridges and tunnels going underwater, the megaproject will shorten a journey that used to take four hours down to just 30 minutes.

Around 4,000 ships a day are anticipated to travel above tunnels, while millions are expected to drive the route. The largest part will include two three-lane expressways.

Over 400,000 tons of steel was used on this bridge, which experts anticipate having a 120-year lifespan. It will be able to survive a magnitude 8 earthquake, a typhoon, or the accidental crash of a large cargo vessel.

Hudson Yards
$20 billion

Take a look at these modern megaprojects.One million square feet of retail and mixed-use space. Eighteen million square feet of commercial and residential space. Over 100 shops. Fourteen acres of gardens, plazas, playgrounds, and public squares. Three parks. Around 4,000 state-of-the-art residences. Over 23,000 construction jobs.

Hudson Yards in New York City is the largest private real estate development in the history of the U.S. and the largest megaproject in the city since Rockefeller Center.

The project is being constructed on two platforms which bridge a working rail yard, 30 active trains, three rail tunnels, and the new Gateway Tunnel.

Many of the innovations established at Hudson Yards—like the rain collection and reuse program that will save 6.5-megawatt hours of energy and offset five tons of greenhouse gas every year—are the first of their kind.

London Crossrail Project
$23 billion

The London Crossrail Project on the new Elizabeth line is the first major tube construction project in 30 years. When completed in December of 2018, builders will have laid 26 miles of new tunnel and constructed 40 new stations.

Crossrail Limited, which was founded in the early 2000s, was set up specifically to tackle this enormous endeavor.

Currently, the formidable project is 85 percent complete. All track has been laid, which allows construction trains to travel the full length of both new tunnels.

Just under a mile of escalators have been installed. Over 9,320 miles of cable, delivering power, lighting, and communication systems have been installed throughout the tunnels. The biggest eye opener? Over 15,000 men and women have worked on the project thus far, with 600 apprentices adding to the 100 million working hours that have been completed.

Dubailand
$64 billion

Dubailand was announced in the early 2000s and survived a halt on construction during the Global Recession. This theme park paradise, due to be completed sometime around 2020, will boast sports venues, eco-tourism, science attractions, hotels, and a three million-square-meter mall.

Dubailand is divided into six zones or worlds: Attractions and Experience World, Sports and Outdoor World, Eco-Tourism World, Themed Leisure and Vacation World, Retail and Entertainment World, and Downtown.

If you’re wondering, yes, it will be bigger than Walt Disney World: two times bigger, actually. The theme park location will also boast the biggest hotel in the world—containing 6,500 rooms—and a public park as big as London’s Hyde Park, increasing the public space in Dubai by an incredible 17 percent.

California High-Speed Rail
$70 billion

With the goal to link San Francisco and Los Angeles, the California High-Speed Rail project anticipates trips less than three hours between the two destinations when complete.

Over 800 miles of track, 24 different stations hitting California’s largest cities, and an expected cruising speed of 220 miles per hour make up this megaproject. If construction can stick to its schedule, it started about two years ago, California’s high-speed rail should complete its first phase by 2029, although service between smaller cities—notably San Jose and Bakersfield—could begin as soon as 2025.

This first phase would take passengers from San Fran’s Transbay Terminal to LA’s Union Station in less than three hours and at an affordable price.

This is the first instance of high-speed electric rails in the U.S., a phenomenon that has already garnered success in several Asian countries.

All transportation agencies throughout California have worked the high-speed rail megaproject into their future transportation and infrastructure plans. The biggest gain? Cali expects the train line will eliminate 10 million miles of vehicle travel daily, and 180 short-haul flights.

This is great news for future commuters of this traffic-ridden state.

South-to-North Water Transfer Project
$78 billion (2014)

This megaproject delivers a much needed commodity to the people of Northern China. The 2,700-mile system of canals and tunnels has brought water to over 100 million people, solving the country’s water crisis and helping 19 cities hit new economic highs.

The scale of this megaproject is almost unfathomable. Throughout the east leg of the project—there are three legs total, two of which are complete—construction teams completed over 400 clean-up projects to eliminate 85 percent of pollutants from the water. In total 510 side projects totalling $3 billion helped eliminate wastewater from the route.

The water is from China’s formidable Yangtze River. The eastern line is over 900 miles long running from the lower Yangtze to Tianjin and the middle line covers the area between Danjiangkou to Beijing. The western line is expected to link the headwaters of the Yangtze and Yellow Rivers, although no set plan has been determined yet.

Completed construction of the water transfer project isn’t expected for another 30 to 40 years. When complete, experts expect over 435 million residents will receive their water from this source.

Al Maktoum International Airport
$82 billion

It comes as no surprise that the advanced technological paradise that is Dubai would host more than one spot on this list. Although the Al Maktoum International Airport opened in 2010, It won’t be fully complete until 2018.

A $32 billion expansion was announced in 2014, making it a focal point for Dubai World Central, which some describe as an airport city. Located about 20 miles outside of Dubai proper, this “airport metropolis” will include everything: commercial and residential buildings, leisure developments, as well as cargo and passenger facilities.

For the first four years of its operation, Al Maktoum was used specifically for cargo operations. The recent expansion facilitated passenger travel.

That not impressive enough for you? When complete, Dubai Airports anticipates Al Maktoum will be able to process 120 million passengers annually, easily making it the busiest airport in the world. The expansion will also allow the airport to accommodate 100 Airbus A380 Superjumbos—at the same time.

By the year 2020, the airport alone could be responsible for nearly 30 percent of Dubai’s GDP, employing 322,000 people and handling an incredible 200 million travelers a year.

International Space Station
$150 billion (2010)

Coming in at a whopping $150 billion as of 2010, the International Space Station (ISS) ranks at the top of our megaprojects list. Future scheduled expansions will have the ISS ringing in at over $1 trillion, making it the single most expensive object ever built.

Created through the partnership between ESA, NASA, JAXA, CSA, and Roscosmos, the ISS ranks as the biggest international cooperative program in science and technology.

It’s as big as a soccer field and currently weighs in at almost 400 tons. The structure is so large that no rocket of modern invention could have launched the ISS into space. Scientists and engineers came up with an innovative solution to get it into orbit: the ISS was delivered into space one piece at a time. It was gradually built—over 40 missions—in an orbit that’s nearly 250 miles above Earth.

Even at this level of cost and complexity, the ISS was not designed to last forever. Sometime after 2020, the ISS will crash into the ocean. Even then, the success of this endeavor between several countries will be its legacy.