Improved path flow estimator for origin-destination trip tables

Path flow estimator (PFE) is a one-stage network observer that can estimate path flows and path travel times from traffic counts in a transportation network. Because a unique set of path flows is readily available from the PFE, a trip table can be estimated by simply adding up flows on all the paths connecting individual origin-destination (O-D) pairs. In this paper, the effects of the number and locations of traffic counts on the quality of the O-D trip table estimated by PFE are examined. The set-covering model, studied in the location theory, is applied to determine the minimum number of traffic counts and their corresponding locations required to observe the total demand of the study network. Next, the effects of the error bounds used in PFE to handle the inconsistency problem of traffic counts are examined, and a heuristic using the Lagrange multipliers to facilitate the adjustment of such error bounds is provided. Numerical results show that PFE can correctly estimate the total demand of the study area if a sufficient number of traffic counts collected at appropriate locations is provided. The results further indicate that improper specification of the error bounds could lead to biased estimation of total demand utilizing the network.