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Title:

How Much Convergence Is Enough for Traffic Assignments Used in Feedback?

Accession Number:

01520033

Record Type:

Component

Availability:

Transportation Research Board Business Office

500 Fifth Street, NW
Washington, DC 20001 United States

Abstract:

Equilibrium travel demand model systems solve for consistency between travel times across a network used by models of travel demand, and the user-equilibrium travel times from assignment of this demand to the network, by means of some form of “feedback” iteration. Within this outer loop is an inner loop of traffic assignment, itself an 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 of these inner loops is sufficient to not prevent, limit, or delay convergence of the outer loops, while avoiding excessive run-time from superfluous over-convergence of tentative solutions. Test results from several Frank-Wolfe assignments varying in congestion level, link flow-delay relations, and region found a fairly consistent relation, within an order of magnitude, between assignment relative gap and a comparable measure of the errors of the resulting origin-destination travel times, compared to those of well-converged assignment. Assignments of several of the same cases with origin-based, projected gradient, or other advanced methods showed larger travel time errors for a given relative gap, with wider variation. In test runs of a feedback model, these results was used to choose adaptive stopping criteria automatically for pre-final assignments, which were lenient in early feedback iterations, and finer as the run progressed. Substantial assignment run-time was saved compared to constant stopping criteria, with insignificant harm to the feedback convergence progress.

Supplemental Notes:

This paper was sponsored by TRB committee ADB30(2) Network Equilibrium Modeling.

Monograph Accession #:

01503729

Report/Paper Numbers:

14-3213

Language:

English

Corporate Authors:

Transportation Research Board

500 Fifth Street, NW
Washington, DC 20001 United States

Authors:

Gibb, John

Pagination:

22p

Publication Date:

2014

Conference:

Transportation Research Board 93rd Annual Meeting

Location: Washington DC
Date: 2014-1-12 to 2014-1-16
Sponsors: Transportation Research Board

Media Type:

Digital/other

Features:

Figures; References; Tables

Subject Areas:

Highways; Planning and Forecasting; I72: Traffic and Transport Planning

Source Data:

Transportation Research Board Annual Meeting 2014 Paper #14-3213

Files:

TRIS, TRB, ATRI

Created Date:

Jan 27 2014 3:07PM