Accuracy in cost estimating under conditions of uncertainty, as is typical of most construction\ud
projects, is an issue of immense concern for clients, project managers, contractors, and all other\ud
stakeholders in construction works. It is an issue of continuing interest and has attracted a lot\ud
of scholarly attention from researchers and innovators. Accurate cost estimates are needed for\ud
planning and budgetary phases of road projects by highway agencies.\ud
Highway projects have historically experienced significant cost overruns often rooted at the\ud
point of the decision to build. However the basis for assessing the level of cost overruns\ud
continues to elicit diverse opinions and has become a debatable issue in the literature, with\ud
some authors alluding to the estimate developed at the detailed design stage as opposed to the\ud
preliminary conceptual estimate as the true benchmark to be used in quantifying the level of\ud
cost overrun.\ud
A survey of literature sources principally from scholarly articles and research programs\ud
undertaken by various highway agencies is carried out, with a view to identifying and defining\ud
the critical phase of development which should constitute the basis upon which investment\ud
estimates are to be predicated. This paper thus evaluates and synthesizes the theoretical basis\ud
of accuracy in estimating, outlines the nomenclature of the developmental phases of highway\ud
projects as evident in the literature and builds upon the argument raised by earlier authors:\ud
Wachs (1989); Simon (1991) and Flyvbjerg et al (2002).\ud
Keywords:\ud
Accuracy of Estimates, Conceptual Estimates, Cost Overrun