An Improved Travel Assignment Process for Project-Level Analysis

This research investigated a restraint assignment procedure which would provide assignment results that are more directly applicable to project-level planning and design. This assignment process was expected to provide more equalized link volume/capacity ratios for the links on the competing roadways within a project area. A prototype assignment model was developed by modifying an existing computer package for urban transportation planning. The assignment results from the prototype assignment model (equalized link v/c ratio assignment procedure) were evaluated to determine whether and how well the link v/c ratios of the links on the competing routes were actually equalized. In addition the accuracy of the assigned link volumes were evaluated by comparing them to the counted volumes. Also, the assigned turning volumes were compared with the results from the incremental restraint assignment technique. Three networks were used for the evaluation; these were the existing network used in the Tyler urban transportation study, a network in which the link capacities were reduced to make the network "congested," and a congested network in which the project area was coded in greater detail.|The research found that for the congested networks, the v/c ratio assignment procedure tended to equalize the v/c ratios for the links on the competing routes within the project area. It produced assigned link volumes which more closely agreed with counted volumes than those from the incremental assignment. Also, the turning volumes produced by this assignment were judged to be more reliable.