A formulation is presented that augments a recently developed method for determining the nonlinear stiffness and damping characteristics of structures subjected to crash-loading environments. The system identification is accomplished using adaptive time domain, constrained minimization techniques. The structural characteristics are idealized with piecewise linear segments and, in the new formulation, the stiffness and damping characteristics are postulated to be functionally dependent. The inertial and material strain rate effects, which constitute the damping characteristics, are modeled as predefined, rate dependent factors applied to the stiffness characteristics. The motivation for this research is to develop lumped mass models of automobiles from acceleration and barrier load data collected during frontal barrier crash testing. The underlying approach in this method is being applied in a global system identification methodology. The application of this methodology towards frontal crashworthiness research projects is discussed.