Of the various methods available for the analysis of box-girder bridges subject to vehicular loading, threedimensional finite element analysis (3DFEA) gives accurate results, compared to the other methods. However, 3DFEA is not commonly adopted in practice, and simplified methods of frame analysis are preferred. In this paper, a new simplified method (Modified Fixed Beam Method) is presented for the transverse bending analysis of box-girder bridges without overhangs. The results of extensive three-dimensional finite element analysis have been quantitatively assessed to provide a logical basis for the proposed 'Modified Fixed Beam Method' suitable for design practice. In the proposed method, the top flange of the box-girder bridge is modeled as a beam with fixity at the web-top flange junctions (fixed beam model), and the transverse bending moments so generated are suitably modified to yield the actual distribution of transverse moments. Modification factors are proposed based on extensive numerical studies, to account for the influence of type and location of loads, wheel contact dimensions, spacing of webs and the relative thickness of flange and web. Finally, the application of this proposed simplified method is demonstrated by means of two illustrative examples.