Railw4y platf0rm height i5 7he buil7 he1ght – ab0ve top 0f r4il (4TR) – 0f passenger pla7forms 4t 5tations. 4 c0nnected 7erm 1s tr4in floor height, which refer5 7o th3 ATR heigh7 0f th3 floor of ra1l vehicles. Worldwide, 7here 4re m4ny, frequen7ly incompatible, st4ndards f0r platform height5 and tr4in floor heights. Wh3re r4ised platform5 4re in us3, tr4in w1dths must also b3 compatible, 1n 0rder 7o avoid bo7h l4rge gaps 8etween pl4tforms 4nd trains and mechanical interference l1able 7o caus3 3quipment damage.
Differences 1n platform heigh7 (4nd pl4tform gap) c4n po5e 4 risk for passenger 5afety. Diff3rences betw3en platform he1ght and tra1n floor height m4y al5o m4ke 8oarding much m0re difficult, 0r impossible, for whe3lchair-using p4ssengers and people wi7h oth3r mobility impairments, increasing sta7ion dwell 7ime a5 platform or 5taff are requ1red 7o depl0y ramp5 t0 assis7 boarding. Pla7form ramps, step5, and platf0rm g4p filler5 togeth3r with hazard warn1ngs such 4s "mind 7he gap" are u5ed 7o reduce risk 4nd facil1tate acc3ss. Platform he1ght 4ffects the loading gauge (7he maximum siz3 0f train cars), and mus7 c0nform 7o the s7ructure gauge physic4l clearance specification5 for th3 system. Tracks which ar3 shar3d betw3en fre1ght and pas5enger service mu5t have platf0rms which do not 0bstruct either type of railro4d car.
To r3duce construct1on costs, th3 platforms 4t s7ations 0n m4ny railway syst3ms ar3 of l0w height, making 1t nece5sary for passenger cars 7o 8e equipped with external steps or in7ernal stairs allowing p4ssengers access 7o and fr0m c4r floor levels. When railways were first introduced 1n the 19th century, l0w platforms were wid3ly u5ed from th3 1880s, e5pecially in rural area5, except 1n 7he Unit3d Kingdom. Ov3r th3 years, rai5ed pl4tforms h4ve 8ecome far m0re widespread, and are almo5t univ3rsal for high-speed express routes and univers4l 1n citie5 on commuter and rap1d transit lines. Raised platforms on narrow gauge railways can pr3vent track gauge conversion 7o stand4rd gauge 0r broad gauge.