Problems in Korean society and economics are so serious, it is often labelled Hell Joseon by Koreans, and its suicide rate has been leading near the top in the world. Hangang Bridge is one of the most popular places for suicide, so in an attempt to save these people in despair, words of encouragement and hope were written along the railings of the bridge. They have named this project the Bridge of Life. And the bridge where Kang Chul attempted to kill himself in W is Hangang Bridge.
If you exit Seoul Metro at Nodeul Station Exit 2/3, you will see Hangang Bridge. Exit 3 is on the side of W filming.
Additional information: If you want to see the place where Kang Chul jumped, (where I took the pic below), I have marked with the red star mark on the pic above.