This project entitled Design, Sizing and Planning of the works of a reinforced concrete girder bridge was carried out in Tunisia. The objective of this work is based on the determination of the geometrical characteristics and the determination of the cross-cutting coefficient (CCC) for the dimensioning of the various elements of the Apron such as beams, spacer and slab. In this work, we used two methods or (approaches) for the determination of the geometrical characteristics of the beams. The study led to the determination of the various fundamental parameters which are the parameter of bracing and the torsion parameter. The conventional method or approach given by the SETRA references, for which the geometrical characteristics of the different sections were obtained by the following formula: Bmoy (m2) = B appui C1 + B central C2; C1 and C2 the interpolation coefficients which describe the variation of the section of the beam as a function of the length and when d= 0.5m. C1 = 1/3 + 4/3Lp = 1/3 + 4/3x21 = 0.3968; C2 = 2/3 - 4/3Lp = 2/3 - 4/3x21 = 0.6032 This for bending inertia and also for torsional inertia. Thus the torsion parameter α = 0.54 and the spacing parameter θ = 1.29.