The　purpose　of　this　paper　is　to　develop　new　formulas　for　live　load　distribution　in　horizontally　curved　steel　I-girder　bridges.　The　formulas　are　developed　by　utilizing　computer　model　results　for　a　number　of　different　horizontally　curved　steel　I-girder　bridges.　The　bridges　used　in　this　study　are　modeled　as　generalized　grillage　beam　systems　composed　of　horizontally　curved　beam　elements　for　steel　girders　and　substructure　elements　for　lateral　wind　bracing　and　cross　frames　which　consist　of　truss　elements.　Warping　torsion　is　taken　into　consideration　in　the　analysis.　The　effect　of　numerous　parameters,　including　radius　of　curvature,　girder　spacing,　overhang,　etc.,　on　the　load　distribution　are　studied.　Key　parameters　affecting　live　load　distribution　are　identified　and　simplified　formulas　are　developed　to　predict　positive　moment,　negative　moment,　and　shear　distribution　for　one-lane　and　multiple-lane　loading.　Comparisons　of　the　formulas　with　finite　element　method　and　grillage　analysis　show　that　the　proposed　formulas　have　more　accurate　results　than　the　various　available　American　Association　of　State　Highway　and　Transportation　Officials　specifications.　The　formulas　developed　in　this　study　will　assist　bridge　engineers　and　researchers　in　predicting　the　actual　live　load　distribution　in　horizontally　curved　steel　I-girder　bridges.　©　ASCE.