Abstract: Simplified equations to calculate deflections and circumferential strains in buried thermoplastic pipe have been developed for AASHTO based on soil-structure interaction solutions. These equations are evaluated here using measurements of HDPE and PVC pipe responses in full-scale laboratory tests. The comparison indicates that the equations are suitable design tools for standard flexible pipe installations. Structural stiffness of the pipes may have an influence on the performance of the deflection equation, since the method overestimated the deflections for a ribbed PVC pipe with high hoop stiffness. The methods for estimating hoop strain and vertical arching factor worked very well for both pipes, and the equation for bending strains provided somewhat conservative values. Recommended design values for constrained modulus of the soil lead to conservative but reasonable predictions in all cases.