The increase in travel cost on the paths is due, in part, to the fact that in this network
two links are shared by distinct paths and these links incur an increase in flow and associated
cost. Hence, the Braess paradox is related to the underlying topology of the networks and,
of course, to the behavior of the travelers, which here is that of user-optimization. One may
show, however, that the addition of a path connecting an O/D pair that shares no links
with the original O/D pair will never result in the Braess paradox for that O/D pair (cf.
Dafermos and Nagurney (1984)).