(eng): Advanced application of ground-based radar interferometry to monitoring of bridges is presented. Using two IBIS-FS interferometric radars, simultaneous determination of vertical and longitudinal displacements of a bridge is possible. The aim of the article is to establish a suitable strategy for determining dynamic and quasi-static response of bridge structures based on the accuracy analysis of measurement by two radars. The necessary theory for displacements determination by means of two radar devices is presented. This is followed by an analysis of errors when measuring with only one radar. Mathematical formulas for accuracy estimation of the resulting displacements obtained by simultaneous measurement with two radars are derived here for the first time in the literature. Practical field examples of bridge structures displacements determination are presented. The key contribution of the paper consists in possibility to estimate the accuracy of the resulting displacements in advance and to plan the achievable accuracy in future measurement.