Hyperloop, a futuristic, high-speed, system of depressurized tubes for transporting people and packages, is still in the early stages of development. First popularized in 2013 by Tesla Motors and SpaceX CEO Elon Musk, it will theoretically send people and cargo through at speeds of up to 760 mph, and yet it’s not totally clear it will even work. But if it does, cities and companies backing the effort want to know just how much it will cost to build, what revenue it will generate once it’s up and running, and what the return on investment will be.
One study conducted by public accounting firm KPMG—and commissioned by FS Links, a partner of Los Angeles-based startup Hyperloop One—determined that a 310-mile proposed hyperloop network connecting the cities of Stockholm, Sweden and Helsinki, Finland would cost $21 billion.
That figure includes everything from the tube people will sit in and the track they will travel along to the civil engineering, allowances for risk, and overhead. The cost even includes 3 billion euros ($3.3 billion) to build one of the world’s longest marine tunnels through the Aland archipelago. This all works out to be about 36.7 million euros per kilometer or about $64 million per mile.
Hyperloop One, the company hoping to snag this particular project, contends that while expensive, it’s still cheaper to build than other high-speed train projects around the world. Hyperloop One offers two examples: UK’s London to Birmingham fast rail project, which budgeted at 100 million euros per kilometer ($180 million per mile) for infrastructure only, and California’s high-speed rail project, which is projected to cost between 69 to 79 million euros per kilometer on average ($124 million to $143 million per mile).
Hyperloop One also argues that the speed, frequency, and convenience of Hyperloop would slash transit time across the region, increase property values on the route and unlock new travel demand by creating a super-metro area of 5 million people.
The KPMG’s initial findings appear to bear this out. The study found that using Hyperloop technology, passengers or cargo could travel from Helsinki to Stockholm in about 28 minutes, a trip that takes 3.5 hours via plane or overnight by a ferry. Trips to Helsinki and Stockholm’s airports from city centers would be slashed to less than 10 minutes, according to the study.
Get Data Sheet, Fortune’s technology newsletter
The study estimates that the value of time saved would equal about 321 million euros a year. Then there’s the ticket sales. The study estimates 43 million passenger trips a year in the complete project. With tickets going for between 20 to 25 euros a pop ($22 to $28), the Hyperloop network would generate revenues of an estimated 1 billion in euros ($1.1 billion) a year. Operating profit would be about 814 million euros ($903 billion) annually, the study says.
FS Links will move forward with a more detailed study, which it says is required to secure the funding and approvals needed to begin construction of a test section along the route. If the project is funded and clears the extensive regulatory and safety hurdles, the domestic networks—the hyperloop in and around both cities—could take about eight years to complete. The section that would link the two countries would take four years, FS Links says.
Based on KPMG’s findings, the city of Salo, Finland, has signed a letter of intent with Hyperloop One to become the first city along the proposed Helsinki-Stockholm route.
Hyperloop One, meanwhile, says it will demonstrate a full-scale, high-speed test of its track, vehicle, and controlled-environment tube in late 2016 or early 2017.
This Startup Wants to Build a Better Hyperloop
Hyperloop One has garnered interest from other cities. Last month, the company, along with Summa Group—the industrial port logistics, engineering, and oil and gas conglomerate owned by Russian oligarch Ziyavudin Magomedov—announced they have signed an agreement with the city of Moscow to explore building high-capacity passenger systems connected to the Russian city’s transport system.
The hyperloop transportation system, which was first popularized in 2013 by Tesla Motors and SpaceX CEO Elon Musk, will theoretically send people and cargo through depressurized tubes at speeds of up to 760 mph.
In May, Hyperloop One held its first open-air test of its propulsion system in North Las Vegas, Nev. At the event, the company announced a number of new global partnerships.
