This paper describes the design, implementation and experimental with an interactive software system which determines the line capacity of a section of running freight trains. The schedules of passenger trains are given. The package can find the effect of decisions related to infrastructure investments like improved signalling, additional stations, additional tracts at stations and additional tracks between the stations in order to improve line capacity. This model was used with test data on an important section (100 kms lenth between 2 major yards with 20 stations) in the Western Railway a zone of the Indian Railways. Experiments were conducted to determine i) the effect of changing a portion of the section from single track to double track; ii) the effect of improved signalling and higher trains speeds; and iii) the best possible starting times for freight trains at either origin.