A Maglev train in Japan. Photo by Junko Kimura/Getty Images.

From the department of keep dreaming: Japan wants to loan the U.S. $4 billion dollars to construct a super-fast “Super Maglev” train between D.C. and Baltimore.

That $4 billion, Japan estimates, would cover half the cost to construct the tracks for the train. According to The Telegraph, a proposal for Japan to lend the U.S. the money to construct the tracks was “first put forward by Shinzo Abe, the Japanese prime minister, during talks with President Barack Obama in February.”

Rather than the traditional model of trains that use wheels on a track, Maglev trains don’t have wheels and are instead propelled along the track using electromagnetic pull, offering a smoother, quieter, and significantly faster ride. But just how fast is it? Well, the Super Maglev trains would move at speeds in the 300 MPH range, putting the D.C.-to-Baltimore trip at just 15 minutes..

But don’t get too excited just yet. Slate’s Matt Yglesias says that the estimated $8 billion cost to build the tracks is probably a gross underestimate. Yglesias explains:

The only problem is there’s no way you could build a D.C.-Baltimore maglev for that kind of money. New York’s Metropolitan Transportation Authority is building a tunnel that would let Long Island Railroad trains go to Grand Central Station and that costs $8.76 billion. Amtrak wants $7 billion to renovate Union Station. The Silver Line of D.C. Metro going from suburban Virginia to Dulles Airport is costing $6.8 billion.

Even if Yglesias is wrong and the track could be built for a cool $8 billion, don’t expect it to go up anytime in the near future. The Telegraph says that the Japan government hopes to have a U.S. Maglev operational “within the next decade.” After that, Japan wants the U.S. to build a Super Maglev track between D.C. and Boston, but who knows when that will be, if ever.