Planning and designing of bridges is part art and part compromise, the most significantrnaspect of structural engineering. One of the initial choices the designer should make is tornselect the most appropriate bridge type for the site. While this choice is not always straightrnforward, selecting the right structure type is probably the important phase of designing arncost-effective bridge. The various types are ideally suited for different span lengths. Forrninstance, on different standards, for spans ten to fifty meters cast in Place Post TensionrnBox Girder Bridges are usually chosen where as for spans ten to one hundred twentyrnmeters Steel Plate Girder Bridge is preferred to be used respectively.rnThis study focused on developing computer program for the analysis and design of Cast inrnPlace Post Tension Box Girder and Steel Plate Girder Bridges, for solving the designrnproblem of economical span and demarking on the base of cost analysis.rnA comparative study based on cost of materials is conducted to select and identify therneconomical span range of Cast in Place Post Tension Box Girder and Steel Plate GirderrnBridges. The program is developed using visual Studio 2012. The developed program isrnillustrated using particular examples for both types of bridges. The study has come withrnsolution based on the current construction prices. As per the study based on the currentrnmaterial cost seventy-meter span is the demarcation span for the two types of bridges.rnWithin the overlap span length of the two bridges, Cast in Place Post Tensioned BoxrnGirder Bridge is economical up to seventy-meter and beyond seventy-meter Steel PlaternGirder Bride be economical.rnKeywords: Bridge, cost effective, cast in place post tensioned box girder, steel platerngirder