It seems that subway projects are only being implemented these days in developing countries in Eastern Europe and Asia, as the Western world says it can no longer afford them. That paradox is particularly true in America, where planners practically eliminated subway options for U.S. cities. It is unfortunate, as subways often remain the best urban transit solution. However, with the advent of new Japanese technologies, the metro option could reemerge on planners’ radar screens. With new low-floor subway cars (based on linear motor propulsion) and substantially smaller diameter tunnels, Japan has shown the world that the cost of underground rapid rail systems can be comparable to large elevated guideways in dense urban environments. Japan is gradually adopting linear induction motor (LIM) subway cars for a reason: The cost of space in its crowded cities is perhaps the most expensive in the world. Line 7 of the Osaka metro system, the second largest in Japan after Tokyo, uses Series 70 LIM drive cars. Each train is composed of four drive cars. The Tokyo Metropolitan Transportation Bureau followed Osaka’s example and now operates LIM driven cars on conventional rails. These new vehicles were manufactured to achieve smaller size inverter control units and other equipment. The bodies were built to lower the floor height (as low as 700mm), maintain ceiling height and increase passenger space with good comfort while greatly reducing the car height to decrease total vehicle size. It is possible to build a smaller, low profile tunnel that is faster to construct and substantially less expensive than a standard size subway. The outside diameter of the low profile tube is 17.5 feet compared to 24 feet for a standard tunnel (those are averages, which vary depending on installation). Generally, the bore of tunnels can be reduced by as much as 50% in a sectional area. With linear motors, which are non-adhesion driven, much steeper grades can be achieved, reducing the required length of a given line. That results in land acquisition and bored material disposal savings, which, in major metropolitan areas, are enormous. In summary, the new design results in a significant reduction in subway construction cost, the magnitude of which generally depends on local urban and soil conditions. Vehicle costs are marginally higher compared with the savings in the overall project cost, and LIM vehicle technology is proven and mature (successfully tested for subway applications in 1984). However, the Guangzhou, China, subway (now being extended) and Bangkok (Thailand) Metropolitan Rapid Transit Authority subway (now in the construction phase) seem to have overlooked the advances in their neighboring country.

—Andrew Jakes
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