  We study the properties of Braess's paradox in the context of the model of
congestion games with flow over time introduced by Koch and Skutella. We
compare them to the well known properties of Braess's paradox for Wardrop's
model of games with static flows. We show that there are networks which do not
admit Braess's paradox in Wardrop's model, but which admit it in the model with
flow over time. Moreover, there is a topology that admits a much more severe
Braess's ratio for this model. Further, despite its symmetry for games with
static flow, we show that Braess's paradox is not symmetric for flows over
time. We illustrate that there are network topologies which exhibit Braess's
paradox, but for which the transpose does not. Finally, we conjecture a
necessary and sufficient condition of existence of Braess's paradox in a
network, and prove the condition of existence of the paradox either in the
network or in its transpose.
