  This paper studies the fundamental communication properties of urban vehicle
networks by exploiting the self-similarity and hierarchical organization of
modern cities. We use an innovative model called "hyperfractal" that captures
the self-similarities of both the traffic and vehicle locations but avoids the
extremes of regularity and randomness. We use analytical tools to derive
theoretical upper and lower bounds for the information propagation speed in an
urban delay tolerant network (i.e., a network that is disconnected at all time,
and thus uses a store-carry-and-forward routing model). We prove that the
average broadcast time behaves as $n^{1-\delta}$ times a slowly varying
function, where $\delta$ depends on the precise fractal dimension.
  Furthermore, we show that the broadcast speedup is due in part to an
interesting self-similar phenomenon, that we denote as {\em information
teleportation}. This phenomenon arises as a consequence of the topology of the
vehicle traffic, and triggers an acceleration of the broadcast time. We show
that our model fits real cities where open traffic data sets are available. We
present simulations confirming the validity of the bounds in multiple realistic
settings, including scenarios with variable speed, using both QualNet and a
discrete-event simulator in Matlab.
