The number of vehicles included in a metered motorway ramp or an urban signalized link at any time is valuable information for real-time control. A Kalman-Filter is employed to produce reliable estimates of this quantity based on real-time measurements of flow and occupancy provided by (at least) three loop detectors. The resulting vehicle-count estimator is tested via microscopic simulation for a variety of metered ramp scenarios and traffic conditions. Several related fundamental issues are addressed: the effects of loop density, update period, downstream signal cycle, vehicle length and link length. The simulation investigations indicate a robust estimation performance with low calibration effort needed, which facilitates easy applicability of the method. (c) 2007 Elsevier Ltd. All rights reserved.