Survey of models to locate sensors to estimate traffic flows

With the advent of Intelligent Transportation Systems, transportation networks are substantially detectorized and large amounts of streaming data is available to manage and plan a multimodal network and provide real-time traffic information to travelers. The related problem of optimally locating sensors on the network to estimate flows has been object of growing interest in the past few years. Available sensors use various technologies and measures different aspects of traffic flows. In this paper we classify the sensor location problems in the literature into two main problems: the Sensor Location Flow- Observability Problem and the Sensor Location Flow-Estimation Problem. We review the existing contributions for the latter of the two problem types and present a unifying bilevel optimization framework, where the upper level addresses the location decisions and the lower level the estimation variables. Several directions for future research are discussed.