In this article, shortcomings of various traditional road sizing methods will be examined and the main conclusion arrived at is the following: they are too simplistic in a set of situations where the elastic layers model cannot be justified. In order to fine tune these methods and make them build on progress made in the domain of geomaterial rheology, it is necessary to use realistic behavioural laws that have been developed in sizing techniques relating to the calculation by the Finished Elements Method for roadway constituent materials. A computation of vertical permanent distortions aggregated over 15 years of traffic on a Cameroonian roadway using the CEBTP-ALIZE method, and then the Finished Elements Method (FEM) was carried out. Results show that distortions derived from the FEM are largely higher than those provided by ALIZE. In order to ascertain the liability of results given by classical methods, it is advisable to confirm them using the Finished Elements Method.