A significant step in the development of Haapamäki railway station was the construction of the Haapamäki–Pori line in the beginning of the 1930s. Due to increased traffic, additional tracks were built on the west side of the railway yard. At the same time, the level crossing north of the station was removed and a flyover was built for the road. Thanks to the Pori line, it was possible for trains to head in four different directions from Haapamäki, which was rare in Finland at that point in time. Thus the number of staff grew and more construction was needed. The depot was enlarged and the wood yard expanded. The Finnish State Railway had a four-story brick building built near the station with 24 apartments for railroad workers. At the same time, a large number of single-family houses were built around the station and 40 single-family houses were built in the Kumpulampi section of the village. Thanks to the new line, the station rose in the ranks, which also affected the increases in the wages that staff received.