How was this performance achieved? The answer appeared to a combination of favourable factors, some of which were natural advantages (e.g., soil conditions) but many due to sound, efficient decision-making and following a comprehensive, priority-based strategy. By setting out very ambitious multi-year financing and construction plans, major technological investments in tunnel-building were amortized early and over large projects.
This appeared to have allowed major capital equipment (such as expensive tunnel boring machinery) to be used more economically over time and over other projects. In the specific case of tunnel-boring equipment, additional machinery was then acquired due to the savings, for a compounding effect as it, too, was amortized. At the time of the Study Tour’s visit, Madrid had an estimated 41 boring machines in operation, including some 30 that were used at one point in subway construction.
Subway construction was done on an uninterrupted, continuous-bore basis, year-in, year-out. Since the boring equipment technology used by Madrid can be operated with very few workers, once the equipment itself was amortized, there was little reason to discontinue its use, even if labour costs involved shift-work and overtime. To avoid adverse impacts on neighbourhoods and commercial enterprises, as well as to avoid buried utilities and structural foundations, tunnel-boring was done at a very deep level.
