A longitudinal joint of the type forming a surface usable as a passage between a first passage surface and a second passage surface adjacent to one another, and usable as walking user passage, the distance between both surfaces (2,3) in the longitudinal direction being variable, wherein said longitudinal joint - comprises a plurality of transverse slats attached to one another, having a substantially planar upper surface, - wherein each of said transverse slats is attached to the contiguous transverse slats by a pivot point with respect to which said transverse slats can rotate, maintaining the continuity of the surface of the longitudinal joint, - wherein the first passage surface comprises an inclined lower surface at its end, a certain number of transverse slats being hidden under said first passage surface, below the level of the upper surface of the longitudinal joint, by means of the relative rotation of the slats to one another with respect to the pivot point, depending on the distance existing between said first passage surface and the second passage surface, characterised in that - the longitudinal joint additionally comprises a first intermediate surface attached to the first passage surface, and a second intermediate surface attached to the second passage surface, configured for supporting the transverse slats, at least part of the second intermediate surface resting on the first intermediate surface, the support area between both surfaces (13,10) being variable depending on the distance between the first passage surface and the second passage surface, and - in that the transverse slats additionally rest on curved support surfaces attached directlv to the first intermediate surface; wherein the first intermediate surface is attached to the first passage surface. - comprises a plurality of transverse slats attached to one another, having a substantially planar upper surface, - wherein each of said transverse slats is attached to the contiguous transverse slats by a pivot point with respect to which said transverse slats can rotate, maintaining the continuity of the surface of the longitudinal joint, - wherein the first passage surface comprises an inclined lower surface at its end, a certain number of transverse slats being hidden under said first passage surface, below the level of the upper surface of the longitudinal joint, by means of the relative rotation of the slats to one another with respect to the pivot point, depending on the distance existing between said first passage surface and the second passage surface, characterised in that - the longitudinal joint additionally comprises a first intermediate surface attached to the first passage surface, and a second intermediate surface attached to the second passage surface, configured for supporting the transverse slats, at least part of the second intermediate surface resting on the first intermediate surface, the support area between both surfaces (13,10) being variable depending on the distance between the first passage surface and the second passage surface, and - in that the transverse slats additionally rest on curved support surfaces attached directlv to the first intermediate surface; wherein the first intermediate surface is attached to the first passage surface.