Низкопольные трамваи: конструкции, преимущества и недостатки.

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.

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 above the rail. The low floor runs right through the articulation of both the long and 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 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
Some public transport companies have both low floor and high floor trams. They report that low floor trams have 15% higher maintenance costs for the rolling stock, and 20% higher maintenance costs for the infrastructure on average. Among the problems observed is that the missing bogies result in a higher level of wear and tear. Many low floor trams have fixed bogies which increase track wear and tear, while decreasing the speed at which a tram can drive through a curve (usually in radius curve). The Škoda ForCity and the newest Alstom Citadis X04 try to counter the effect with low floor pivoting bogies while maintaining 100% low floor design. Prior to the new design, pivoting bogies could only be used under high floors, hence such trams could only be part low floor, with high floor sections over the pivoting bogies.

The idea of a low floor tram dates back to the early 20th century when a number of trolley systems began experimenting with various "stepless" designs. Perhaps the most notable is the Hedley Doyle Stepless car introduced in 1912 for use on Broadway in Manhattan. A number of other cities also purchased Hedley Doyle Stepless trams after seeing their success in Manhattan. Since these cars had a unique appearance compared to any other trams running at the time, they earned a number of nicknames, including hobble skirt cars, public welfare cars, and sow bellies.