“Of the 11 million passengers who climb aboard one of 8,520 trains each day, about 550,000 have reserved accommodations. Their journeys can start in any part of India and end in any other part, with travel times as long as 48 hours and distances up to several thousand kilometers. The challenge is to provide a reservation system that can support such a huge scale of operation — regardless of whether it is measured by kilometers, passenger numbers, routing complexity, or simply the sheer scale of India.” (Center for Railway Information Systems Web site, http://www.cris.org.in)
Srivastava, Shirish C.; Mathur, Sharat; and Teo, Thompson, "Modernization of Passenger Reservation System: Indian Railway's Dilemma" (2006). ICIS 2006 Proceedings. 98.