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EFFECTIVE SLAB WIDTH FOR COMPOSITE STEEL BRIDGE MEMBERS SUMMARY The objectives of this work were to (1) propose criteria for effective width and recommended specifications and commentary for effective width and (2) provide worked examples illustrating the use of those proposed new criteria. The principal focus was common slab-on-girder configurations. A new definition for effective width that accounts for the variation of bending stresses through the deck thickness has been needed. A finite element modeling approach was developed, corroborated with experimental data by others and by the authors, and applied to a suite of bridges designed according to industry guidelines. Effective widths accord- ing to the new definition were extracted from this finite element parametric study of the suite of bridges. Principal findings from the parametric study were as follows: (1) full width was typically acting "at cross sections where it is most needed," i.e., where moments and hence performance ratios would be highest, and (2) where the effective width was less than full width at such cross sections, that cross section had consider- able excess flexural capacity. Draft criteria for effective width were developed by applying regression approaches in order to account for different subsets of the parameters varied in the extensive para- metric study of bridge finite element models. The effects of those criteria were assessed using the Rating Factor (RF) as the measure of impact. Based on the impact assess- ment, draft criteria based on using the full physical slab width were recommended and illustrated in the context of positive and negative moment region worked examples.