In order to better adapt to the demand of vehicle detection

based on the superposition principle

the theoretical derivation of the magnetic perturbation generated by the vehicle is given and the analytical formulation of the relationship between magnetic induction and vehicle position is developed. Two AMR senors are used to measure the magnetic field from the vehicle and to estimate relative position and parameters from measurement in real time. The experimental results show that the method has good feasibility for determination of the vehicle position and magnetic feature parameters.