This paper presents a fast engineering tool for the analysis of the mechanical fields in cracked pavements. The pavement structure is reduced to three elastic and homogeneous equivalent layers resting on a soil. The soil is modelled by one layer, named shear layer, connected to Winkler's springs in order to ensure the transfer of shear stresses between the pavement structure and the springs. The whole four-layer system (3 pavement layers connected to the shear layer) is modelled using a simplified model (M4-5n) developed for the analysis of delamination in composite materials. For the case of 2D plane strain, a system of twelve equations is written analytically. These second order differential equations are solved by the finite difference method (Newmark). In the case of a pavement containing a vertical cracking through one layer, the half-analytical solutions are obtained in less than one second CPU. This tool, called M4-5nW, thus allows parametrical studies such as the distribution of mechanical fields (especially interface stresses) as function of the load position more or less distant from the vertical crack. This new modelling shows its effectiveness compared to the use of a conventional finite element code.