01559070

Component

Equilibrium travel demand model systems solve for consistency between travel times across a network used by models of travel demand, and resulting from user-equilibrium assignment of this demand, by means of some form of “feedback” iteration with successive averaging. Inside this outer loop, user-equilibrium traffic assignment is its own iterative process solving for consistency between times traveled on the network and on the shortest paths between each origin and destination. This study examines how fine a convergence criterion of these inner loops is sufficient to not prevent, limit, or delay convergence of the outer loops, while avoiding excessive run-time from unnecessarily fine convergence of tentative assignments. A key to determining such criteria is the relation between an assignment’s relative gap and the error of the origin-destination times, relative to well-converged assignment; an empirical investigation is presented. A fairly stable relationship, within an order of magnitude, appears among numerous test cases of conventional link-based assignments. A moderately higher error shows from origin, path, and bush-based assignments. A method using these results is presented to choose adaptive stopping criteria automatically for pre-final assignments, so they begin lenient in early feedback iterations, and adjust finer as the run progresses. In test runs in a feedback model, run-time of the early assignments reduced substantially compared to constant stopping criteria, the added perturbation had only mild, temporary effect, and the model reached its convergence limits in less time.

This paper was sponsored by TRB committee ADB30 Transportation Network Modeling.

01550057

15-3130

English

24p

2015

Transportation Research Board 94th Annual Meeting

Digital/other

References; Tables

Methodology; Origin and destination; Stopping; Traffic assignment; Travel demand

Data and Information Technology; Highways; I72: Traffic and Transport Planning

Transportation Research Board Annual Meeting 2015 Paper #15-3130

TRIS, TRB, ATRI

Dec 30 2014 1:03PM