Sampling strategies for two-fluid model parameter estimation in urban networks

James C. Williams*, Hani S. Mahmassani, Robert Herman

*Corresponding author for this work

Research output: Contribution to journalArticlepeer-review

16 Scopus citations


The basic postulate of the two-fluid theory of town traffic relates the average speed of moving vehicles to the fraction of moving vehicles in a street network; both representing averages over all vehicles in the network. Data collection to provide estimates of the model parameters to-date has consisted of sampling the network with a test car, replicating (as closely as possible) the trip histories of randomly selected vehicles in the network. Because the two-fluid model is nonlinear, it cannot be simultaneously applied at the individual vehicle level and the network level, as is shown in this article. However, due to the practical difficulties in collecting data for all the vehicles in the network, several potential sampling strategies are identified and are evaluated with computer simulation. The simulation experiments suggest that aggregating the trip histories of 10 to 20 test vehicles over 10 to 15 minutes yields parameter estimates very close to the true value.

Original languageEnglish (US)
Pages (from-to)229-244
Number of pages16
JournalTransportation Research Part A
Issue number3
StatePublished - May 1995

ASJC Scopus subject areas

  • Civil and Structural Engineering
  • Transportation
  • Management Science and Operations Research


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