Passengers wait to board the subway at Line No. 9's Gimpo International Airport Station during the morning rush hour. (Yonhap)

The Seoul Metropolitan Government announced Wednesday that it will add eight six-carriage trains on Line No. 9 of the Seoul Metro, increasing the number of trains in operation from the current 45 to 53 by early 2024.

Out of the eight that are planned to be added, five will begin operating from this weekend on Dec. 30.

With the newly added trains, the city government plans to reduce train arrival intervals and extreme overcrowding during rush hour.

By the year-end, train arrival intervals are expected to decrease, so that trains will arrive every 3 minutes and 25 seconds, shorter than the current interval of 3 minutes and 40 seconds.

The intense overcrowding on Line No. 9 express trains is expected to decrease from the current 199 percent to 182 percent after the five new trains are added.

The official capacity of one train car is 160 people. But currently, an average of 250 people cram into a single car on Line No. 9 during rush hour.

When all eight trains are added to Line No. 9, overcrowding levels are expected to decrease from 199 percent to 168 percent over-capacity, and arrival intervals are expected to decrease by 30 seconds. For all-stop trains, overcrowding is expected to decrease from 128 percent to 117 percent over-capacity after the five trains are added and to 108 percent after all eight trains have been added.

During rush hour, commuters are often packed onto express trains on Line No. 9, which runs between Gaehwa and Gimpo International Airport and VHS Medical Center, as it stops at major subway stations near business districts like Yeouido and Gangnam.

With the increase in train numbers, the total number of trains on Line No. 9 during rush hour will also increase from 64 to 70, increasing the total official carrying capacity to 96,810 passengers from 88,512.

According to the city government, these eight trains on Line No. 9 could cost up to 86.4 billion won ($66.7 million).

Meanwhile, the Seoul Metropolitan Government also announced on Tuesday that a total of eight trains will be added on Line Nos. 4, 7 and 9 from 2024 to 2027. Out of the eight, three will be added to Line No. 4, one will be added to Line No. 7 and four will be added to Line No. 9. This is in addition to the eight extra trains that will be added to the last line by early 2024.

The latter addition will cost up to 100 billion won, of which 25.6 billion won will be covered by the central government.