Assessment of Procurement Methods and Their Impact on Bridge Construction Outcomes in Kwara State

The choice of procurement method for bridge construction projects significantly influences project performance, quality outcomes, and the achievement of public value in infrastructure delivery. This study assesses the impact of different procurement methods on bridge construction outcomes in twelve projects executed in Kwara State in the North Central geopolitical zone over a six-year period. Projects procured through open competitive tendering, restricted tendering, direct labour, and design-and-build arrangements were compared across outcome metrics including cost performance, schedule adherence, technical quality, and post-construction maintenance demand. Project documentation was reviewed and interviews conducted with engineers in the Kwara State Ministry of Works, resident engineers, and consultants involved in project delivery. Cost and schedule performance indices were calculated for each project. Results indicate that design-and-build projects achieved the best schedule performance, completing on average 12 percent ahead of open tendering equivalents, attributable to the integration of design and construction responsibility enabling concurrent engineering. However, design-and-build projects showed lower technical quality scores in bridge deck detailing and drainage design, reflecting client-side capacity limitations in reviewing contractor-led design submissions. Direct labour projects demonstrated the worst cost performance, with overruns averaging 58 percent due to plant and material management inefficiencies. Open competitive tendering combined with a detailed employer's requirements specification and independent supervision produced the best overall quality outcomes. The study advocates for procurement method selection guidance documents for state ministries of works and capacity building for client-side design review in design-and-build contracts. Keywords: procurement methods, bridge construction, Kwara State, project performance, design-and-build.