We now describe a general network equilibrium model with elastic demands due to Dafermos
(1982) but we present the single-modal version, for simplicity. It is assumed that one
has associated with each O/D pair ω in the network a travel disutility function λω, where
here the general case is considered in which the disutility may depend upon the entire vector
of demands, which are no longer fixed, but are now variables, that is,