  We consider the problem of coordination via signaling in network congestion
games to improve social welfare deteriorated by incomplete information about
traffic flow. Traditional studies on signaling, which focus on exogenous
factors of congestion and ignore congestion externalities, fail to discuss the
oscillations of traffic flow. To address this gap, we formulate a problem of
designing a coordination signal on endogenous information about traffic flow
and introduce a it self-fulfilling characteristic of a signal that guarantees
an outcome flow consistent with the signal itself without causing the unwanted
oscillation. An instance of the self-fulfilling signal is shown in the case of
a Gaussian signal distribution. In addition, we show simple numerical examples.
The results reveal how a self-fulfilling signal suppresses the oscillation and
simultaneously improves social welfare through improved network efficiency.
