| Summary: | The research set off with the rationale of understanding the cause of the unusually high cost overruns experienced in highway projects, executed in the tropical wetland setting of the Niger Delta region of Nigeria. An expansive range of research from academe, revealed a strong dialectical debate between the theoretical and technical schools of thought, as to what propagates relatively higher cost overruns in public infrastructure projects. The theorists posit that optimism bias and deliberate misrepresentation by project planners, largely accounts for cost overruns in transportation infrastructure projects, and not geology/geotechnical risk as tendered by the technical school. Yet the literature continues to report inadequate geotechnical risk containment resulting in considerable post-contract cost overruns in highway projects. As a result of this contradiction, and the lack of a robust empirical analysis to this effect, this research was carried out to explore the statistical validity of geotechnical risk factors in explaining cost overruns recorded in highway projects executed in the Niger Delta region. Using the case study research strategy, 16 interviews were conducted within the 3 highway agencies in the region, longitudinal cost data was also gathered from 61 completed highway projects, along with geotechnical index data on the engineering properties of sub-grade soils at project locations. These were comprehensively analysed using an innovative multi-method approach: Thematic analysis; Documentary/archival analysis; Spatial analysis of geotechnical data sets, designed to quantitatively converge in a triangulatory log-regression model. The results of regression analysis identified that latent pathogens such as heterogeneous ground conditions and non-adherence to geotechnical best practices, amidst a wide array of unanticipated social constructs, account for the majority of the recorded variance between the initial estimates and the project’s final account. The interplay of the emergent social constructs with the latent pathogens was further cognitively mapped out, using content analysis, to visually conceptualise the relative weightiness of the intricate complexity of the contextual dynamics, driving the unusually high level of cost overruns experienced in highway project delivery in the Niger Delta. The study concluded that the phenomenon of cost overruns in highway projects is multi-hydra headed, driven by a complexity of technical and contextual social variables, and not the simplistic explanations implied by the dichotomous arguments in the literature. It was thus recommended that tackling cost overruns in highway projects require far more than the scientific application of technical risk management tools, and should therefore, further incorporate concerted and specifically targeted efforts at curbing the intrinsic contextual triggers within, and external to highway organisations.
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