Experimental and numerical analyses have shown that the stress in unbonded materials is carried by force chains that primarily affect only some particles while leaving others rather lightly loaded. This localization of strains and stresses is essential to the behavior of granular materials. Analysis based on the Hertz’s theory leads to relationships similar to equations proposed by Hardin and Richart for the shear modulus and Hicks and Monismith for the resilient modulus of road materials. Road materials in natural and compacted states are essentially anisotropic. This condition conflicts with the assumption of isotropy used in most mechanical computations in geotechnical engineering. Two key processes are at the base of anisotropy of any material: its deposition mode and its history of stresses. From the macroscopic point of view, most road materials behave as orthotropic materials whose elastic properties are symmetrical around the vertical axis.