Evolution of railway network flexibility: The Spanish broad gauge case

The length of the Spanish broad gauge network has decreased in the 1956-2006 period. When looking at different railway maps through this period, it seems that the network is offering fewer and fewer alternatives when a line is cut, that is, the network is becoming less and less flexible. The goal of this article is to prove that the flexibility of the Spanish broad gauge network has decreased substantially in the 1956-2006 period. We have considered the network as a graph (ignoring traditional railway quality indicators such as commercial speed, number of tracks, electrifications, signaling, …) and we have chosen two simple indicators as accurate in this sense: the number of cycles (cycles provide an alternative to reach a station if there is a problem in one line) and the number of stations of intermediate degree. To achieve this, we have developed a piece of software that is an ad hoc extension of Maple's networks package.