Expanding the parametric city model for the structural design of two-technology transit systems, with an application to Santiago

Investment in urban public transportation involves strategic decisions regarding the organization of transit lines in the urban space and the choice of their technology in addition to the size of both fleet and vehicles of each line, and their spacing (lines density). The parametric city model (PCM) of Fielbaum et al. (Transp Res Part B Methodol 94:298-338; Netw Spat Econ 17:343-365) was created to conceive and decide a structural design - the first step of the strategic design - in real size problems, representing the city through zones and centers and evaluating predetermined lines-structures considering a single technology. In this paper the scope and capabilities of the PCM are expanded to help the structural design of urban transit systems, by opening the search for the type of lines-structures studied and considering two technologies (modes), noting that the simplified representation constitutes a useful tool for transport policy that departs from the usual "black-box" procedures. The approach is applied to a PCM version of Santiago, Chile, showing that schemes different from feeder-trunk might be convenient. The results support the options presently taken in Santiago based upon subway expansions but changing the role of the bus system.