Non-Unique Solutions of User-Equilibrium Assignments and Their Practical Implications

The user-equilibrium (UE) assignment is widely used in predictions of travel on roadway systems. It is well known, that under appropriate assumptions, total link flows are uniquely determined by the UE assumption, but route flows are not. Route flows have become increasingly important in practical applications as the variety of analyses performed on traffic assignment results expands. The purpose of this paper is to examine the extent by which results of analyses may be influenced from this issue of non-uniqueness. As a case study, we use a medium size network for the roadway system in Israel. We employ a new assignment algorithm to obtain a precise UE solution, and to determine the set of UE routes in this solution. Random processes are used to generate 450 alternative route-flows UE solutions and 1000 alternative origin-based-link-flows solutions. The effects of differences among solutions are analyzed at the route level and for two types of applications: "select link" analysis and license plates surveys. The results show that for almost every OD pair with multiple UE routes the route flows are nearly completely arbitrary. Substantial arbitrariness remains in aggregate analyses as well; for example for 9% of the links the origin cannot be determined for at least half of the flow.

• Corporate Authors:

  Transportation Research Board

  500 Fifth Street, NW
  Washington, DC  United States  20001
• Authors:
  • Bar-Gera, Hillel
  • Luzon, Amos
• Conference:
  • Transportation Research Board 86th Annual Meeting
  • Location: Washington DC, United States
  • Date: 2007-1-21 to 2007-1-25
• Date: 2007

Language

• English

Media Info

• Media Type: CD-ROM
• Features: Figures; References; Tables;
• Pagination: 14p
• Monograph Title: TRB 86th Annual Meeting Compendium of Papers CD-ROM

Subject/Index Terms

• TRT Terms: Network links; Origin and destination; Route choice; Traffic assignment; Traffic flow; Traffic lanes; Travel; Travel patterns; Trip length
• Uncontrolled Terms: User equilibrium
• Geographic Terms: Israel
• Subject Areas: Highways; Planning and Forecasting; I72: Traffic and Transport Planning;

Filing Info

• Accession Number: 01046973
• Record Type: Publication
• Report/Paper Numbers: 07-1335
• Files: TRIS, TRB
• Created Date: Apr 26 2007 8:38AM