A low-floor tram is a tram that has no stairsteps between one or more entrances and part or all of the passenger cabin. The low-floor design improves the accessibility of the tram for the public, and also may provide larger windows and more airspace. An accessible platform-level floor in a tram can be achieved either by using a high-floor vehicle serving high-platform tram stops, or with a true low-floor vehicle interfacing with curb level stops. Currently both types are in use, depending on the station platform infrastructure in existing rail systems. Some systems may make use of former railway alignments where use of existing high platforms is desirable, while others, particularly new systems, may not have the space to site high-level stops in urban centres. Low-floor tram configurations Trams traditionally had high floors, and these designs evolved into the tram with a low-floor centre section. Examples of this design are Amsterdam 11g/12g-trams and the Kusttrams in Belgium. The most common design of 100% low floor vehicles uses short carbody sections for the wheels and longer suspended sections. Examples of this are the Alstom Citadis and Combino. A similar, but somewhat older technique is one that has been developed by MAN. In 1990, it was the first 100% low floor tram. These trams are found in ten German cities (such as Bremen and Munich) and in the Swedish city Norrköping. In many other German cities there are trams with low floor between the outer bogies and single axle bogies under the centre section. "Light rail" type vehicles frequently have a similar configuration but with a centre bogie designed to accommodate a low floor situated under a short centre section. A more radical approach has been adopted for the City Class LRV (Citytram), where the main low floor section is only 300 mm above the rail. The low floor runs right through the articulation of both the 29 m long and 38 m Super Citytram version. In both, the corridor through the articulation is wide enough for seated passengers and a wheelchair to pass through. The City Class has been designed to turn on 15 m radius curves and to climb 10% gradients. In Austria, Porsche Design designed Ultra Low Floor (ULF) Trams can "kneel" at the curbside, reducing the height from the road to only 180 mm. Some public transport companies have both low floor and high floor trams. They report