This report presents the results from a research project financed by the Swedish National Road Administration. In this project an instrument composed of computerised galvanostatic supplier and data acquisition system has been developed at SP for electrochemical measurement. With the help of this instrument, different measurement conditions and parameters could be evaluated and many electrochemical measurement data could be collected for later analysis. A numerical model based on a 2-D FEM (2-Dimensional Finite Element Method) has been established for modelling the corrosion measurement. With the help of this model, the measurement parameters could be optimised and the effectively confined current could be evaluated. Based on the results of numerical modelling and the studies on the small and big reinforced concrete slabs, a rapid method for measuring corrosion rate has been developed. The method involves a short time galvanostatic pulse measurement followed with the numerical calculation for correcting the preset polarisation current from the measured data, so as to produce “true” resistance values related to the confined area. Owing to its rapidity (in a few seconds per measurement), this method provides a useful tool for mapping corrosion rate of reinforcement steel in concrete structures. The results from a comparative measurement on both small and big reinforced concrete slabs show that the corrosion rate measured by the new rapid method is quite comparable with that measured by Gecor, which uses the modulated confinement technique. The results from the field measurements on two old concrete bridges also show that the corrosion extent measured by the new rapid method is in good agreement with the visual observations.