Imagine a tiny self traveling along in one of the air-powered containers used in drive-through banks. That thought experiment (or something akin to it) happened at some point in the mind of the boldly entrepreneurial Tesla Motors founder Elon Musk, and on Aug. 12 he began to publicly push his tube-and-air concept in earnest. In a blog on the Tesla Motors website, he links to a pdf that describes the idea—he calls it Hyperloop—in a conceptual way with drawings and some engineering calculations that he admits need much more fleshing out to be workable. He believes that his transportation solution would work for travel distances of less than 1500 km (900 mi)—supersonic air travel being the more reasonable solution for extreme-speed travel at greater distances. Musk said he believes an above-ground Hyperloop system would be a better solution for reducing travel time between Los Angeles and San Francisco than high-speed rail, proposals for which he ridicules in his blog. Among the trickiest Hyperloop engineering challenges is the Kantrowitz Limit, which says that the speed limit of a pod inside a tube is determined by the ratio of the area of each. To overcome the Kantrowitz Limit (a possible newcomer to the popular lexicon if the Hyperloop idea gains traction), Musk proposes electric compressors to move high-pressure air from the front of the pod to the rear. Musk clearly is an idea man who by the following quote can be assumed to also have a good sense of humor: "Short of figuring out real teleportation, which would of course be awesome (someone please do this), the only option for super-fast travel is to build a tube over or under the ground…"