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Development, Testing and Evaluation of a Nodal Restraint Assignment Procedure

Chen Yuan-WangJ. D. BensonGeorge B. Dresser

出版	Texas Transportation Institute, The Texas A&M University System, 1992
URL	http://books.google.com.hk/books?id=1bJxGYy7BCsC&hl=&source=gbs_api

註釋

This dissertation developed and evaluated a traffic assignment procedure in which capacity restraint was applied to nodes instead of links. The conventional traffic assignment techniques consider alternative paths through a successive impedance adjustment process in which link impedances (travel times) are adjusted based upon the ratios of the assigned link volume to a coded link capacity. In reality, the capacity of a urban street system is constrained by intersections (nodes) instead of links. The procedure was developed by utilizing the concept of the intersection sum of critical lane volumes in the Highway Capacity Manual 1985. A nodal impedance adjustment subroutine was incorporated in the assignment process to account for intersection delays where link impedance were held constant and nodal impedances were updated from iteration to iteration. The nodal impedance for each turning movement at a node is determined by the association of all the movements encountered at the node (i.e., the impedance of a movement at a node is a function of all the movements entering the node). The nodal restraint assignment procedure then was applied to a test network (Preston Road Corridor in North Dallas). In the application, various assignment procedures and different impedance adjustment function parameters were used to test robustness of the proposed procedure. The impedance values produced by the nodal impedance subroutine were examined to determine if they were correct according to the computation algorithm. The convergence rate of the proposed procedure was inspected as well. The stability of the proposed procedure was examined through various network performance measures. The nodal restraint assignment was evaluated through comparison with the selected best of the available conventional capacity restraint assignments, based upon traffic counts at major intersections along Preston Road. The evaluation was based on various micro-level analyses which included measures of mean difference and root mean square errors of approach volumes, analysis of turning movements as a percentage of approach volume, and paired t-tests of approach volumes and turning movements. These analyses show that the nodal restraint assignment generally produced better turning movement replications than the available capacity restraint assignments.