Railways have adopted different track gauges for a variety of reasons: geographical conditions or restrictions, construction costs, military security etc. When through-operation is not possible on railways because of different track gauges, passenger and freight traffic is obstructed with resultant negative effects on rail transport and commercial activities. For example, most European railway networks adopted the standard 1435mm gauge, whereas those of Spain and the former Soviet Union adopted broad gauges of 1668mm and 1520mm, respectively. Therefore, through-operation of trains was not possible between France and Spain, the former Soviet Union and Poland or the now defunct East Germany, etc. To overcome these difficulties, various measures have been devised such as changing the gauge, changing trains in the case of passenger traffic, freight transshipment, exchanging of running gears and development of gauge changeable trains. Of these, the latter option may offer a suitable solution as the others are both time-consuming and expensive. To design a gauge changeable train, on the other hand, it was necessary to address the following issues: (1) the development of a mechanism that could change and lock the wheelset gauge safely and securely; (2) the making of durability and weight reduction improvements to the additional gauge changing and locking components and (3) decreasing the complex gauge changing truck's production and maintenance costs. For these reasons, the Talgo-RD passenger cars in Spain were the only examples already in operation. Recently, Spain, Poland, Germany, Japan, and other countries have also been making technological advances in the development of new gauge changeable trucks or wheelsets.
    To cut the time needed to change locomotives that pull Talgo-RD passenger cars, Patentes Talgo in Spain has been developing the Talgo XXI diesel-hydraulic or electric locomotive haulage type trainset equipped with the same gauge changing mechanism adopted for the Talgo-RD passenger cars. In addition, Spanish rolling stock manufacturer Construcciones y Auxiliar del Ferrocariles (CAF) is developing the new BRAVA variable gauge wheelset system with powered trucks, trailing trucks for passenger cars, and a projected maximum speed of over 220 km/h.
    In Poland, SUW2000 gauge changeable wheelsets have been in service on both passenger and freight services since 2000 to achieve through-operation between Poland (standard 1435mm gauge) and Lithuania (broad 1520mm gauge), once part of the former Soviet Union. The maximum speeds of the truck equipped with the SUW2000 system are 160 km/h for passenger cars and 120km/h for freight cars.
    In Germany, Radsatzfabrik Ilsenburg has been developing the DBAG/Rafil Type V variable gauge wheelsets for freight wagons jointly with the Minden Research Center. These variable gauge wheelsets are being tested on regular freight services involving gauge changing operations. The above-mentioned Talgo XXI, BRAVA, SUW2000, and DBAG/Rafil Type V are all available for changing between both 1435mm and 1520mm, and 1435mm and 1668mm gauges.
    In Japan, the Railway Technical Research Institute (RTRI) has been developing gauge changeable EMUs which enable through-operation between Shinkansen (standard 1435mm gauge) and conventional (narrow 1067mm gauge) lines, under the guidance of and subsidized by the Ministry of Land, Infrastructure and Transport, and as contractor to the Japan Railway Construction Public Corporation. However, we have had to make further technological advances in the development of this gauge changeable truck concept because : (1) truck construction has become more complex, this gauge changeable EMU system requiring each truck to be fitted with a power unit; (2) the construction of the wheelset and truck is more intricate than in the case of changing gauges between 1435mm and broad gauges, because the gauge changing range narrows from standard 1435mm gauge to narrow 1067mm gauge; and (3) gauge changeable EMUs in Japan have to demonstrate both high-speed running stability when running on Shinkansen lines and high-speed curving performance on conventional lines. At present, the development of these gauge changeable EMUs is being undertaken by the Technology Research Association for Gauge Changeable Trains established last August and with which RTRI is also closely collaborating.