The numbers are pretty unbelievable -- at a top speed of 760 miles per hour (more than 1,200 kilometers per hour), the so-called hyperloop proposed by entrepreneur Elon Musk could whisk travelers from New York to Washington in 29 minutes, one-fifth the time needed by Acela, Amtrak’s fastest train. Now, Musk appears to have scaled down those ambitions somewhat, at least for an early version of the idea. He has won a bid in Chicago to build a high-speed express train to its O’Hare International Airport. It’s not quite a signed contract yet, but if the parties proceed, it will give Musk a chance to prove parts of his untested technology.