This thesis presents an automated workflow in MATLAB to optimize a steel through-truss railway bridge. The objective focuses exclusively on reducing the self-weight of the bridge by decreasing the structural sections of its main members while keeping the overall geometry fixed. The process integrates a parametric model and automated structural analysis within an optimization loop that avoids manual iteration. The constraints consider Ultimate Limit States (ULS) and Serviceability Limit States (SLS), including resistance checking, buckling, serviceability deformations, as well as fatigue criteria for the elements and dynamic behavior (vibrations) under railway loads. The results indicate that it is possible to achieve lighter designs while maintaining safety and operational requirements and reducing the calculation effort and trial-and-error typical of conventional design.