Time Cost Relationships For Public Road Construction Projects In Ethiopia

This research work has tried to test the time – cost relationship of road projects by using thernhypothesized empirical and graphical models developed for the concept. Based on thernEmpirical Bromilow’s Model, the duration of Ethiopian Federal Road Construction Projectsrnhas been modeled by a time - cost formula expressed in the form of T = KCB, where T is thernactual construction time in calendar days, C is the final cost of contract in Ethiopia Birr, K isrna constant characteristic of time performance, and B is a constant indicative of the sensitivityrnof time performance to cost level. This thesis applied the relationship to 33 projects based onrnthe two categories International Contractor (IC) and Domestic Contractor (DC) Projects andrnon the adjusted and unadjusted cost basis.rnAnalysis using both linear and multiple regression technique was performed between projectrnduration (i.e., time), project cost, project length and type of construction (asphalt concrete,rndouble surface treatment, and gravel surface). The analysis results indicated that the abovernprinciple is valid to IC projects and is invalid to DC projects based on T – test. Though thernBromilow’s principle has been found to invalid for DC projects, the relationship betweenrncontract Time and length has been developed. In addition the research has developed a costrnprediction model for IC projects.rnBased on the Graphical Model, the time – cost relationship has been reviewed by using therncumulative time – cost curve(S – curve) concept and the earned value managementrntechniques (EVM). The applicability of this curve was tested by using two case studyrnprojects. The test for smoothness of the curve was carried out by testing the reliability indexrnusing Weibull probability functions. In addition to that EVM techniques like SchedulernVariance, Schedule Performance Index and Estimate to Completion were used to view theirrnapplicability. The analysis results clearly indicated that the S- curve concept is not applicablernto the case study projects and the tools of EVM technique are better indicators of thernperformance than the S – curve.rnKey Words: Construction Management; Time - Cost relationship; Bromilow’s Principle; SCurve;rnEarned Value Management.

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