A broad gauge connection between Vijayawada Junction and Chennai Central opened the following year, enabling rail travel between Hyderabad and Chennai (then Madras). The Hyderabad-Godavari Valley Railways was established in 1900 with the opening of the Manmad-Secunderabad metre gauge line, and merged into the NGSR in 1930. In 1916, the Kachiguda railway station was built as NGSR headquarters and to regulate traffic at Secunderabad. Diesel rail cars manufactured by Ganz were tried for the first time in Hyderabad State by the NGSR in 1939. On 5 November 1951, Nizam's Guaranteed State Railway was nationalized by the government of India and merged into the government-owned Indian Railways (IR) as part of the Ministry of Railways. The Secunderabad station was assigned to the Central Railway zone, with Victoria Terminus its headquarters. In 1966, the South Central Railway zone was formed with Secunderabad its headquarters (as well as the headquarters of Indian Railways' Secunderabad Division. Rail Nilayam (the zone headquarters) was built in 1972, and the division headquarters was built in 1980. The Indian Railway Institute of Signal Engineering and Telecommunications (IRISET), one of IR's six centralised training institutes, was established in Secunderabad by the Ministry of Railways on 24 November 1957. to address the specialised training needs of railway staff and officers in railway signalling and telecommunications. In 1967, the Ajanta Express was introduced between Kachiguda and Manmad via Secunderabad. With an average speed of , it was India's fastest metre gauge train at the time. The Secunderabad–Vijayawada Junction Golconda Express was introduced in 1969. The country's fastest steam train, with an average speed of . it was later extended to Guntur. In February 1978, the Secunderabad Division was split into two divisions: Secunderabad and Hyderabad. Although an early computerised reservation system began at Secunderabad in July 1989, the 30 September 1989 introduction of SCR's computerised Passenger Reservation System (PRS) at the station made reservations easier. The system, later linked to New Delhi (1997), Howrah (1998), Mumbai and Chennai (both 1999), preceded the CONCERT reservation system which was developed at Secunderabad in September 1994 and implemented in January 1995. The Secunderabad–Mahbubnagar metre gauge section was converted to broad gauge in 1993, breaking an important north-south meter gauge freight connection north from Secunderabad.