High-speed ground transportation ( HSGT) technologies with vehicle speeds exceeding 150 mph can be divided into two basic categories; High-speed rail (HSR) systems, with top speeds between 150 and 200 mph, use steel wheels on steel rails, as with traditional railroads, but can achieve higher speeds because of the design of both the rail bed and cars. High-speed magnetic levitation (MAGLEV) systems, with top speeds between 250 and 300 mph, use forces of attraction or repulsion from powerful magnets placed in either the vehicle or the guideway beneath it both to lift the vehicle above the guideway and to propel it forward. A MAGLEV vehicle can be likened to a flying train or a guided aircraft. If linked effectively with highways and air service, HSGT technologies—particularly MAGLEV—could have a significant impact on congestion in the future. When comparing HSR with MAGLEV technologies, MAGLEV appears to be the technology of choice. Though the new generation of HSR technology can reach commercial speeds of up to 186 mph, additional increases in speed pose great engineering problems, suggesting that rail transportation is a mature technology. MAGLEV technology, on the other hand, is in its infancy and will improve substantially with additional engineering.