A Comparison of Traffic Assignment Techniques

This report compares and evaluates the traffic assignment results from five assignment techniques: all-or-nothing, stochastic multipath, iterative, incremental, and equilibrium. The results of the assigned volumes from the five techniques are compared to ground counts. Various statistical measures are used to evaluate the results. Five different assignments of the existing Tyler, Texas, network were compared to ground counts to determine if there were differences among the results. Measures of how well the assignment reproduces traffic counts were divided into two groups: macro-level measurements (screenlines, cutlines, and VMT) which are network-wide analyses and micro-level measures which are link-by-link comparisons.|No significant difference was found among the five assignment techniques when using the macro-level measures. The values for the incremental assignment had the best results compared to ground counts when using micro-level measures.|Some of the statistical measures were affected by the introduction of capacity restraint. Otherwise, it was concluded that the incremental and the equilibrium assignments represented a slight improvement from the all-or-nothing and the stochastic multipath assignments. However, the difference in results was not significant enough when using capacity restraint to warrant the extra cost such as link capacity data and computer run time involved in the capacity-restraint assignments. This implies that much of the precision in the assignment procedure using the different techniques may be sacrificed and still produce acceptable assignment results.