Implementation of an Equilibrium Capacity Restraint Model in the Texas Large Network Assignment Package (1153-6F)

One of the major objectives of Study 2-10-89-1153 has been to improve the accuracy of the assignment models implemented in the Texas Travel Demand Package. Three areas for improvements of the Texas capacity restraint model were identified: improved techniques for estimating iteration weights using an equilibrium approach; user-supplied impedance adjustment functions which can vary by functional class; and an option for computing link impedances which provide for variable weighting of time and distance.|While never implemented in the Texas Large Network Assignment Package (Texas Package), the equilibrium assignment procedure has become a widely used procedure in operational studies over the past 10 years. The principal difference between the equilibrium model and the capacity restraint procedure implemented in the Texas Package in 1979 is in the iteration weights. In the current Texas capacity restraint procedure, the analyst specifies the weights to be used in combining the iterations. In equilibrium assignments, these iteration weights are computed to minimize the impedance for each trip.|An equilibrium capacity restraint assignment procedure, therefore, was implemented in the Texas Package. The procedure was implemented as an option in both the ASSIGN SELF-BALANCING and PEAK CAPACITY RESTRAINT routines. The documentation manuals for these routines were also revised.