A methodology was developed to incorporate the structural contribution of working platforms, including those constructed with industrial byproducts, into the design of flexible pavements. Structural contribution of the working platform was quantified with the 1993 AASHTO flexible pavement design guide in terms of a structural number or an effective roadbed modulus. Two methods are proposed. One method treats the working platform as a subbase layer and assigns a structural number to the working platform for use in computing the overall structural number of the pavement. The other method adjusts the effective roadbed modulus to account for the improvement in the roadbed provided by the working platform. Resilient modulus obtained from large-scale model experiments conducted on several working platform materials (e.g., breaker run stone, Grade 2 gravel, foundry slag, foundry sand, and bottom ash) was used in the analysis. Design charts show the structural number or the roadbed modulus as a function of type of material and thickness of the working platform.