An efficient public transport system, such as the Subway, can be use as an indicator of how developed one country is. Subway is known differently in different part of the world, e.g. Metro, Tube, MRT and Underground etc.
Designing and constructing an underground transport system, it is not as easy as it may seem, it needs a complex and hollistic view of what the country will be in the future.
Underground utilities, electrical wiring, pipelines, sewerages need to relocated accordingly, the inside of the Subway itself need to be aesthetically pleasing.
Subway can be commercialise, small kiosks, shops, banks, restaurants and cafe etc, can be considered and built into the subway planning, so that it could attracts more user, where in the long run, could minimise the ground traffic congestion.
The Seoul City's Subway system consist of about 9 lines, with the general interval of about 2~6 mins (depending if it is during the rush hour or not), and the ticket can be considered quite reasonable, about +/-US$1 per trip, according to the distance.
In total, more than 7 million commuters use the subway daily. The subway map is also available in English, hence it is quite easy to navigate yourself around.
BTW, here are some images of the Seoul City Subway..... some people read books, mags, papers in filling the time in travelling.. and some take photos of others... hehe
(Click the above image for a larger version).