Here is a question about this article: In the south, land up to Safdarjung's Tomb was acquired in order to create what is today known as Lutyens' Bungalow Zone. Before construction could begin on the rocky ridge of Raisina Hill, a circular railway line around the Council House (now Parliament House), called the Imperial Delhi Railway, was built to transport construction material and workers for the next twenty years. The last stumbling block was the Agra-Delhi railway line that cut right through the site earmarked for the hexagonal All-India War Memorial (India Gate) and Kingsway (Rajpath), which was a problem because the Old Delhi Railway Station served the entire city at that time. The line was shifted to run along the Yamuna river, and it began operating in 1924. The New Delhi Railway Station opened in 1926 with a single platform at Ajmeri Gate near Paharganj and was completed in time for the city's inauguration in 1931. As construction of the Viceroy's House (the present Rashtrapati Bhavan), Central Secretariat, Parliament House, and All-India War Memorial (India Gate) was winding down, the building of a shopping district and a new plaza, Connaught Place, began in 1929, and was completed by 1933. Named after Prince Arthur, 1st Duke of Connaught (1850–1942), it was designed by Robert Tor Russell, chief architect to the Public Works Department (PWD).
What is the answer to this question: The Imperial Delhi Railway was built to transport workers and materials for how many years?
twenty years