The concept of equilibrium is an abstraction because of the simplifying assumptions that
it entails. As noted, travelers are assumed to choose O-D routes that require minimum time (or
disutility). Accordingly, travelers are assumed to know, and accurately perceive, travel times
throughout the network, presumably through numerous trials of different routes to be able to identify their minimum travel time route given any congestion scenario. Finally, O-D flows and
roadway characteristics are assumed to be fixed and known.