地 can also be used as a particle and is then pronounced "de" (it seems this is the "default" pronunciation for this character when it's all alone) but when it means "ground"/ "land"/ "earth"/ "field" or part of compounds it's pronounced "dì".
The subway systems in Taiwan (including Taipei and Kaohsiung) are also called MRT. But in Mandarin Chinese we call them "捷運/捷运"(jiéyùn), though the concept is generally the same as "地鐵/地铁".
In theory you could add 的 here but it's not necessary. It's like saying 'the station of the subway' or 'the subway's station'; it kind of makes sense but it's not very natural.