State-run railroad operator KORAIL is set to mark the 40th anniversary of the opening of Seoul’s subway system Friday.

As of August 2014, KORAIL operates 12 subway lines that speed through 228 stations, up from just three subway lines and 29 stations when it started its service in 1974. KORAIL’s subway trains run 2,454 times a day, carrying more than 3 million passengers.

The total travel distance is estimated at 109,223 km, equal to approximately 2.7 times the circumference of the Earth. The busiest subway station is Yeongdeungpo station, which hosts some 112,000 commuters and passengers on a daily basis. KORAIL’s push to expand the subway system and its services has helped improve the quality of life and reshape the country’s transportation infrastructure.