The current design provisions (2006 edition of CSA-S6) for horizontally curved steel I-girders in the Canadian Highway Bridge Design Code are based on research conducted prior to the mid 1980's. Much research, experimental and numerical analysis, on horizontally curved girders has been conducted over the past 30 years. A review of the available data was conducted and areas where more information is required were identified. Although extensive research has been conducted on horizontally curved I-girders, there were limited experimental and numerical results on girders with flanges that were Class 3 or better that failed below 80% of the beam's yield moment. Elastic and inelastic lateral torsional buckling failures typically occur below 80% of the beam's yield moment. A parametric study was conducted, focusing on lateral torsional buckling behaviour of horizontally curved girders. The parametric study included a total of 36 single horizontally curved girder models that varied the following parameters: the radius of curvature, the flange width-to-thickness ratio, and the web height-to-thickness ratio. The parametric study was conducted using finite element analysis. The development of the finite element models included validating the models by comparing with previous experimental and numerical results. Different curved girder design equations were explored, and three were chosen to be investigated. They were compared based on the actual moment resistances found from the models to determine which equation performed best. Based on the analysis results, the proposed equation for the 2014 edition of CSA-S6 best predicts the actual moment resistance for curved girders. The mean calculated-to-actual moment resistance ratio was 0.90 and the coefficient of variation was 0.10 for first-order analyses, 0.98 and 0.08 respectively, for second-order analyses.