The bridge network within the United States is aging quickly, and many of these bridges are reaching their intended design limits. A large portion of these bridges will need to be repaired or replaced in the near future, and to avoid the high costs of replacing these bridges simultaneously, techniques to ensure safe life extension of these bridges are necessary. Using structural response modification techniques, it is possible to safely extend the life of these bridges. This paper applies a response modification apparatus, consisting of a response modification device that adds supplemental damping and stiffness and a mechanical amplifier, to a numerical model of a realistic in-service bridge with fatigue vulnerable components. By using the scissor jack mechanical amplifier, a smaller response modification device, can be utilized to provide large response reduction forces. Numerical results of the computed moments and deflections using the proposed method are compared to numerical results of the computed moments and deflections of the model without the response modification approach. Reductions in moment and deflection achieved by the approach are up to 42 percent and 28 percent, respectively, and a fatigue life increase in excess of 400 percent is achieved. Additionally, the efficacy of the response modification apparatus is compared to that of another previously proposed response modification apparatus without a mechanical amplifier, and the proposed apparatus with the amplifier is shown to clearly outperform the other apparatus. From the results, it is clear that response modification techniques show promise to extend the life of fatigue vulnerable bridge structures.