This article aims to analyze the changes in freight transport on Thai Railways during World War II. This was largely influenced by the introduction of Japanese military transport shortly after the war began diverting freight transport away from Thai Railways. While the reduction of transport volume on the East Bank line (the Northern, the Northeastern, and the Eastern lines) was remarkable, the rate of decrease on the West Bank line, or the Southern line along the Malay Peninsula, was relatively low. The large gap between two lines that pre-existed the war reduced steadily. The most important role of Thai Railways in pre-war period was the transport of freight (primarily rice, pigs, and wood) from the inland regions in the North and Northeast to the entrepôt at Bangkok. This was greatly affected by the reduction in transport capacity after the outbreak of the war resulting in a further decrease of civil freight transport by Thai Railways.

At the same time, transport capacity on the Southern line was less than that on the East Bank line. As such, necessities such as rice and salt continued to be transported on the Southern line. As alternative methods of transport, particularly water transport, were halted due to the war, the importance and value of the Southern line continued to increase. Furthermore, this helped to support its use in transporting civil freight.

Before the war, the focus of Thai Railways had been on transporting freight from the inland regions to Bangkok via the East Bank line. However, during the war, the importance of this line was reduced by the introduction of Japanese military transport. Instead, the focus of Thai railways became the West Bank line in an effort to address the shortage of necessities on the Malay Peninsula. As a result, the West Bank line reached its peak during the war as it was not only central to Thai Railways transport routes but also those of the Japanese military.