It is worth mentioning that policies, in the form of tolls, for example, can be applied to
guarantee that the travellers behave in a manner that, after the imposition of tolls, is also
optimal from a system-optimizing perspective. For some background, see Dafermos (1973),
Nagurney (2000), Lawphongpanich, Hearn, and Smith (2006), and the references therein.