Set-Valued Estimation of Freeway Traffic Density

The information about traffic density on a freeway is required by real time traffic responsive ramp flow controllers. Currently, density cannot be measured directly and has to be estimated from traffic flow and/or velocity measurements.This paper describes the algorithm for the set-valued density estimation using the macroscopic first order Cell Transmission Model (CTM) together with combined flow and velocity measurements. It is assumed that freeway cell capacities, on-ramp demands and measurement noise values are not known exactly, but lie within certain intervals. Monotonicity of CTM allows to reduce density estimation to a series of interval arithmetic operations.