The observability problem in traffic network models

This article deals with the problem of observability of traffic networks, understanding as such the problem of identifying which is the subset of OD-pair and link flows that can be calculated based on a subset of observed OD-pair and link flows and related problems. Two algebraic methods for solving the observability problems are given, one global approach based on null-spaces and a step by step procedure allowing updating the information once each item of information (OD-pair or link flow) becomes available. In particular, seven different observability problems are stated and solved using the proposed methods, which are illustrated by their application to the Nguyen-Dupuis network problem. The results show that the proposed methods provide useful information on which OD-pair or link flows are informative on other OD-pair and link flows, and that the methods are applicable to large networks.