The aim of this paper is to study the design requirements for rigid intermediate transverse stiffeners in longitudinally stiffened plate girders. Firstly, two representative design codes, AASHTO and EN 1933-1-5, are discussed and compared. Then the results of two tests on 1.5 m deep plate girders and the results of the extensive numerical parametric study are presented. The analysis of the results shows that the axial force in the stiffener due to tension field action is overestimated in the design codes and that all the design requirements for rigid transverse stiffeners can be covered by defining a minimum required second moment of area.