Effect of inadequate design on cost and time overrun of road construction projects in Tanzania: a case study of central corridor road upgrading projects

Completing road construction projects within budget and time has been a problem for TANROADS and the major problem highlighted in all projects is inadequate design. However, the extent to which inadequate design contributes to both time and cost overruns as well as its causes have remained under-studied. The objective of this study was therefore to determine the extent, the causes as well as the ways to alleviate the problem. The methodology used to accomplish the study objectives included identifying recently completed central corridor road upgrading projects, reviewing their project completion reports and holding roundtable discussions with consultants and TANROADS officials of the design section. Cost and time overruns on seven projects reviewed averaged 44% and 26% respectively. Similarly, the extents to which inadequate design contributes as a percentage of all cost and time overruns are 61% and 85% on average respectively. These overruns were predominantly related to problems that occurred during design process prior to construction, including: errors and omissions of some works and key costs in the BoQ during design, poor topographical survey, inadequate geotechnical/materials investigation and poor determination of the size and/or number of drainage facilities. In order to eliminate/reduce the problem, it has been recommended to TANROADS to properly manage design projects, enhance the review process of design reports, adhere to the state-of-the-art especially to introduce RSA during design, have a road geometric design manual and review the staffing level to match with the available work-load.