  As part of the effort undertaken to understand urban environments and their
generation, we need to explore models that produce statistically valid
configurations of roads. These sort of models will help us to derive plausible
mechanisms for the spatial location of population.
  This task is of fundamental importance, as we need to create an experimental
environment that allows us to disentangle the specificities of a spatial
configuration from the ideal system. Creating statistically valid models of
road networks along with models of city generation allows to average the
effects of geometry bringing us one step closer to understanding urban
environments.
  To completely understand road networks we need to be able to grasp what
principles of economy do their growth entail. It is therefore of interest to
explore the possible shape that a performance function would have for
transportation systems.
  In this work, we tackle this issue by proposing a network generation model
based on a single parameter $\alpha$ which is capable of creating any type of
network from trees to quasi-surfaces and which is shown to generate networks
close to the real road networks under study. This is obtained through the
definition of local and weighted versions of centrality measures. These
centrality measures deal with distance-decay effects and nodes having different
masses.
  We set ourselves to determine the properties and different regimes of this
$\alpha$-model and we lay out a definition for the performance of a network
taking into account factors such as robustness, construction cost, congestion
and distance. We obtain the optimal alpha from the analysis of the space of
possible performance functions, giving an intuition on the self-organisational
properties of the original network.
