Empirical evidence suggest that most urban systems experience a transition
from a monocentric to a polycentric organisation as they grow and expand. We
propose here a stochastic, out-of-equilibrium model of the city which explains
the appearance of subcenters as an effect of traffic congestion. We show that
congestion triggers the unstability of the monocentric regime, and that the
number of subcenters and the total commuting distance within a city scale
sublinearly with its population, predictions which are in agreement with data
gathered for around 9000 US cities between 1994 and 2010.Comment: 11 pages, 12 figure