with heavy rail vehicles, these passenger vehicles usually also use high floor designs. Existing tram/streetcar/light-rail networks generally feature low platforms as many of the stations or stops are in the streets. The high construction/conversion cost of high platforms and the difficulty of making high platforms compatible with other features of the urban landscape are a significant obstacle to converting tram networks these into urban or commuter rail networks with high platforms. These problems were a major motivation for the development of low-floor trams, which allow transit operators to avoid the retrofitting of high platforms on existing routes, while still providing improved accessibility. Although low-floor vehicles began to be developed in the 1920s, the first low-floor tram is generally recognized as the Duewag/ACM Vevey design of 1984 deployed in Geneva, providing a floor height of ATOR. Bus Tourist coaches generally have very high floors, sometimes greater than above the road surface, in order to have ample room for luggage under the floor. Since boarding must be allowed directly from flat ground, long and steep staircases are needed. Transit buses also use high floors to provide mechanical clearances for solid axles, but the use of dropped axles has enabled the creation of low-floor buses and by 2008 in the United States, the majority of new transit bus orders were for low-floor types. Use Europe Germany Today, in Germany, all rapid transit railways, most commuter trains, and many light rail vehicles operate as high-floor networks. A notable exception is the city railway in Cologne; in the mid-1990s, it was decided to divide that city's partially high-platform network into two separate networks: high-floor and low-floor. In contrast with some light rail underground lines, which are often provisionally equipped with low platforms or with tracks laid on raised ballast, there are new developments in the German cities of Düsseldorf (Wehrhahn line) and Dortmund (east–west line). In each of these cities, a new underground light rail line is equipped with platforms for low-floor trams and will be permanently operated with low-floor vehicles. This form of design and construction will avoid the need for subsequent rebuilding of stops on tram routes, even though both cities already have underground lines with high-floor platforms. North America United States In San Francisco, the Muni Metro light-rail system, which has both on-street and underground stations, uses a combination of high and low platforms, and the vehicles feature retractable stairs to accommodate