A microscopic investigation and estimation of rail line capacity are essential in the planning, design, and operation of railway facilities. This research aims at assessing the effects of railway vertical alignment at uphill sections on railway line capacity as well as on capacity loss at such a railway segment. The evaluation of operation and geometry data to estimate rail line capacity and capacity loss due to rail geometric alignment change was conducted using the backup method of semi-simulation analysis tool from THSRC in Taiwan. A Log-linear type regression model was developed to formulate the relationship between rail capacity loss and uphill alignment characteristics. The developed model is capable of analyzing regular rail capacity and capacity changes due to factors of geometric alignment as well as rail operational setting.