The billionaire behind companies including SpaceX and Tesla Motors has unveiled his plans for a futuristic new transportation technology he’s calling HyperLoop. The high-speed train works like those tubes at bank drive-throughs—except instead of a canister, sleek pods travel on a cushion of air at 800 mph. Though Elon Musk’s initial plan is to build a HyperLoop that would travel between Los Angeles and San Francisco, he says that the technology could also make traveling between other cities much faster. Musk estimates that it’ll cost around $7 billion to turn his vision into a reality. The entrepreneur says that “Hyperloop is considered an open-source transportation concept,” and he hopes others will contribute to the design. He’s even posted a detailed, 57-page initial design plan online for free. Consider this our contribution to the design …