Capturing time-varying link flows

Project titleCapturing time-varying link flows and their properties in road traffic network modelling

Project duration:  Nov. 2001 - Nov. 2004.

Project staff:    Principal Investigator: Professor Malachy Carey
                         Research Fellow, Dr Y. E. Ge


Several different approaches have been adopted internationally to modelling traffic flows varying over time on congested road networks (referred to as dynamic traffic assignment, or DTA).  But even when these are applied to the same simple scenario (e.g. a within-day model with no learning behaviour, tolls, variable controls, etc) they produce different results, since each type of DTA models tends to have different link-flow model(s) embedded within it. Also, the present versions of some link-flow models in use in DTA have serious deficiencies or unexamined or not well understood properties.  In view of this, we propose to investigate and compare the properties and behaviour of link flow models used in DTA, and how these affect the relative performance of DTA models.  We will do this in several ways, both theoretically and numerically, and will also investigate swapping link flow models between DTA models, where this is possible, to develop improved models. The most interesting aspect of the research is that our investigations to-date indicate that if various seemingly quite different approaches to link flow modelling are refined/ improved (particularly with appropriate discretisations), then they converge to give similar results, thus promoting consistency, comparability and transferability between approaches.

Papers to-date related to the project.

1.       CAREY, M.  "Dynamic traffic assignment with more flexible modelling within links".  Networks and Spatial Economics 1(4), 349-375. Sept. 2001.  (Special issue on "Foundations of Dynamic Traffic Assignment").

2.       CAREY, M. and M. McCARTNEY, "Behaviour of a whole-link travel time model used in dynamic traffic assignment".  Transportation Research 36B(1), 83-95, Jan. 2002.

3.       Ge. Y.E. and M. Carey (2002). Link outflow rate computing under continuous dynamic loads.  Pages 770-777 in Traffic and Transportation Studies, Proceedings of ICTTS2002, July 23-25, 2002, Guilin, China.  Edited by K. C. P. Wang, G. Xiao, L.Nie and H. Yang, published by ASCE, Virginia.

4.       WIE, B.-J., R.L. TOBIN and M. CAREY,  "The existence, uniqueness and computation of an arc-based dynamic network user equilibrium formulation,"  Transportation Research 36B(10). 897-918, Dec. 2002.

5.       CAREY, M,  Y.E. GE and M. McCARTNEY,  "A whole-link travel-time model with desirable properties".  Transportation Science 37(1), 83-96, 2003. 

6.       CAREY, M. and M. McCARTNEY,  "Pseudo periodicity in a travel-time model used in dynamic traffic assignment".  Transportation Research 37B(9), 769-792, 2003.

7.       CAREY, M. and Y.E. GE,  "Comparing whole-link travel time models used in DTA".  Transportation Research 37B(10), 905-926, 2003.

8.       CAREY, M. and M. McCARTNEY, "An exit-flow model used in dynamic traffic assignment".Computers & Operations Research 31(10), 1583-1602, 2004.

9.       CAREY, M. "Link travel times I: desirable properties”,Networks and Spatial Economics 4(3), 257-268.

10.     CAREY, M. and Y.E. GE, “Efficient discretisation of link travel time models used in DTA.” Networks and Spatial Economics 4, 269-290, 2004.


11.     CAREY, M. “Link travel times II: properties derived from traffic-flow models”, Forthcoming in Networks and Spatial Economics.

12.     CAREY, M. and Y. GE,  "Convergence of whole-link travel time models used in DTA".  Forthcoming in Transportation Science

13.     CAREY, M. and Y. GE, “Alternative conditions for well-behaved travel-time functions".Forthcoming in Transportation Science.