Wikipedia
High-floor is an expression used to distinguish tram, light rail and other rail vehicles, along with buses and trolleybuses, built to formerly conventional design, from their counterparts of low-floor design.
A rail vehicle of high-floor design usually has a flat floor between and above the top of the railhead. For reasons of accessibility, an attempt is made to standardize the height, to allow a stair stepless entry from high platforms. The increased construction cost of high platforms, and the difficulty of making them compatible with other features of the urban landscape, are a significant obstacle to the conversion of existing tram networks into urban rail networks, particularly when many of the stations or stops are in the streets.
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. However, for a newly constructed route, a route primarily located in tunnels, or a route with a dedicated right of way and enough space, high platforms are usually preferred, since high-floor vehicles are cheaper to manufacture, and have better operating characteristics.
High platforms do have significant advantages beyond wheelchair accessibility (except for double-decker trains). Mobility-impaired passengers (e.g. those using canes or who have difficulties climbing stairs) also benefit, as do travelers pulling wheeled luggage or small folding shopping carts. Even fully able-bodied passengers can board a railcar more rapidly if they do not have to climb stairs to enter, reducing dwell time at a stop, and reducing overall travel time. In addition, high-platform railcars have more floor space for passengers if space is not required for stairways, and wheelwells needed to accommodate railcar bogies.
Tourist coaches generally have very high floors, sometimes above 1 meter, 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.