Seoul City announced a temporary bus transportation plan as part of efforts to alleviate crowding on a newly extended subway line, officials said Sunday.

Five new stops opened on Subway Line No. 9 from Sinnonhyeon Station to Sports Complex Station in southeastern Seoul on Saturday. The extended service is expected to attract about 3,000 additional daily passengers, the city said.

In a bid to reduce rush-hour crowding, the city government said it would offer a number of free alternative buses on the subway route from Gayang Station in the west to Yeouido. It will also run free Yeouido-bound express buses in the mornings from three spots ― Gimpo Airport Station, Gayang Station and Yeomchang Station.

The city also vowed to dispatch 50 safety guards to the stations to control the crowds.

Concerns have escalated as the city expected that the transportation congestion rate of Subway Line No. 9 would rise to about 240 percent in the rush hour once the extended service starts. A congestion rate of 100 percent equates to having 158 passengers in one subway car.

Construction began on Subway Line No. 9 in 2008, with about 50 percent currently running. The line is set for completion in 2018, the city said.

By Lee Hyun-jeong (rene@heraldcorp.com)