Metal bridge span comprising two adjacent parallel longitudinal support girders (10a, 10b), the metal bridge span resting on two spaced-apart supports and being constituted by the assembly of three types of element produced in advance, namely: - elongate modules (3, 31, 32) having at least one same length and each equipped, at at least one end, with means (12, 16) for removable assembly with a corresponding end of an adjacent elongate module (3, 31, 32) to form the two adjacent parallel longitudinal support girders (10a, 10b), such that the two longitudinal support girders have a respective length corresponding to the distance between supports, - transverse spacer beams each having two ends having means for removable fixing to conjugate means formed on the opposing lateral walls of the elongate modules (3, 31, 32) of the two adjacent parallel longitudinal support girders (10a, 10b), and - flat deck elements extending between said adjacent parallel longitudinal support girders (10a, 10b) and bearing on said girders, characterised in that: - each elongate module comprises two spaced-apart flat soles, namely a lower sole and an upper sole connected by a vertical core constituted by a rectangular flat sheet, so as to configure a girder with an l-shaped cross-section, - said core has two opposite lateral faces (90, 91) to which there are fixed a plurality of transverse flat elements extending vertically over the entire height of the core, which flat elements are distributed over the entire length of the elongate module and are spaced apart from one another by a constant pitch corresponding to a sub-multiple of that length, said flat elements each forming a stiffening rib having a vertical side welded to the core and two spaced-apart horizontal sides welded to the opposing inside faces of the two soles (7, 8), said ribs each being equipped, in their upper portion, with means for the removable fixing of a transverse spacer beam end, which means are positioned at the same level relative to the upper soles of the elongate modules (3, 31, 32) of the two adjacent parallel longitudinal support girders, - at least one of the adjacent parallel longitudinal support girders (10a, 10b) is constituted by at least two adjoining elongate modules having the same length and the same height, and - the stiffening ribs formed on the opposing inside faces of said adjoining elongate modules are in pairs facing one another and are rigidly connected together in order to secure said adjoining elongate modules, which then behave like a single girder element. - elongate modules (3, 31, 32) having at least one same length and each equipped, at at least one end, with means (12, 16) for removable assembly with a corresponding end of an adjacent elongate module (3, 31, 32) to form the two adjacent parallel longitudinal support girders (10a, 10b), such that the two longitudinal support girders have a respective length corresponding to the distance between supports, - transverse spacer beams each having two ends having means for removable fixing to conjugate means formed on the opposing lateral walls of the elongate modules (3, 31, 32) of the two adjacent parallel longitudinal support girders (10a, 10b), and - flat deck elements extending between said adjacent parallel longitudinal support girders (10a, 10b) and bearing on said girders, - each elongate module comprises two spaced-apart flat soles, namely a lower sole and an upper sole connected by a vertical core constituted by a rectangular flat sheet, so as to configure a girder with an l-shaped cross-section, - said core has two opposite lateral faces (90, 91) to which there are fixed a plurality of transverse flat elements extending vertically over the entire height of the core, which flat elements are distributed over the entire length of the elongate module and are spaced apart from one another by a constant pitch corresponding to a sub-multiple of that length, said flat elements each forming a stiffening rib having a vertical side welded to the core and two spaced-apart horizontal sides welded to the opposing inside faces of the two soles (7, 8), said ribs each being equipped, in their upper portion, with means for the removable fixing of a transverse spacer beam end, which means are positioned at the same level relative to the upper soles of the elongate modules (3, 31, 32) of the two adjacent parallel longitudinal support girders, - at least one of the adjacent parallel longitudinal support girders (10a, 10b) is constituted by at least two adjoining elongate modules having the same length and the same height, and - the stiffening ribs formed on the opposing inside faces of said adjoining elongate modules are in pairs facing one another and are rigidly connected together in order to secure said adjoining elongate modules, which then behave like a single girder element.