Elon Musk proposed the Hyperloop, a transportation system consisting of passenger capsules that travel at airline speeds through a low pressure tube. The capsules are elevated above the tube surface by air bearings to reduce friction and are propelled using a compressor powered by solar energy. The Hyperloop aims to provide fast, safe travel between cities by eliminating grade crossings and having a top speed of 1200 km/hr. Currently, Hyperloop Transportation Technologies is building a test track in California to demonstrate the technology.