The design of bridge decks requires accurate transverse live load distribution; however, existing simplified methods like beam models fail to capture cross-section bending and distortion, while traditional Load Distribution Factors (LDFs) provide only approximate values for the most stressed beam. This study introduces a novel method to fill this gap by applying a virtual model that reduces the structural problem to two degrees of freedom per longitudinal rib: deflection and rotation. Unlike prior models, this approach explicitly accounts for increased torsional and transverse bending stiffness in box sections and incorporates distortion through a reduced shear area calculation. The methodology was validated through a parametric study of 75 box-girder decks involving 175 load states, alongside two experimental tests: a small-scale laboratory section and a full-scale load test of the Arlanzon Viaduct. Findings demonstrate a maximum divergence of less than 14% compared to traditional Finite Element Methods (FEM), with a mean error below 8%. Experimental results showed an accuracy level comparable to complex FEM models. This method significantly optimizes calculation time and material resources, offering a reliable alternative for bridge design using modern materials without requiring high computational power.