ABSTRACT
A network design problem (NDP) is a common decision-making problem that arises in urban transportation planning when selecting improvements or additions to an existing network to decrease traffic congestion or pollution, or other appropriate objectives. NDPs, according to their characteristics, are classified into several types. If the link improvement variables are 0-1 integers or continuous variables, then either a discrete problem or a continuous problem can be formulated. Chen and Alfa (1991) further divided the problems into three groups: (a) those with linear objective functions, (b) those with non-linear objective functions, the solutions of which satisfy the system-optimal criterion, and (c) those with non-linear objective functions, the solutions of which satisfy the user-optimal equilibrium criterion.
