India's railways were re-organised into regional zones beginning in 1951 with the creation of the Southern Railway on 14 April and the Central Railway and Western Railways on 5 November. The post of Chief Commissioner of Railways was abolished and the Railway Board adopted the practice of making its senior-most member chairman. In the same year, the government of West Bengal entered into an agreement with Calcutta Tramways Co. to take over its administrative functions. On 14 April 1952, the Northern Railway, the Eastern Railway and the North-Eastern Railway were created. On 1 August 1955 the South-Eastern Railway was split from the Eastern Railway, and, the following year, divisional systems of administration were set up for the various regional zones. In 1958, the North-Eastern Railway split to form a new Northeast Frontier Railway.