THESIS ABSTRACT

Abstract

For a construction project to be successful, it is essential to prepare a realistic contract estimate and assign a practical contract duration. This study aims to perform assessment of the time duration estimation models for Design–Build and Design–Bid–Build procurement methods for bridge construction projects implemented under the Department of Roads. A Sequential Explanatory Mixed Methods Design methodology is adopted using data collected from 40 completed bridge projects executed between Fiscal Year 2018/19 and 2023/24, comprising 20 DB projects and 20 DBB projects. Contract documents, completion reports, Extension of Time (EoT) records, Variation Orders, and Key Informant Interviews with professionals served as data sources for this research. The study employed descriptive statistical analysis, time duration estimation using DoR contract duration estimation guidelines and Bromilow’s Time-Cost modelling of bridge projects procured under DB and DBB approaches. DB projects demonstrated comparatively better schedule and cost performance, with an average time overrun of 41.10% compared to 132.10% for DBB projects. Similarly, DB projects achieved slight cost savings of 0.39%, whereas DBB projects experienced an average cost overrun of 5.33%. Current DoR duration guidelines systematically underestimated completion times for both delivery systems. BTC regression models also yielded low goodness-of-fit and substantial predictive errors; MAPE value for DB and DBB contracts being 39.07% and 49.66% respectively. The regression cost sensitivity coefficient () for DBB contracts was nearly three times that of DB contracts. The results suggested that existing duration estimation guidelines and single-variable models failed to capture the complex risks inherent to bridge construction in Nepal. Replacing cost- only estimation models with Multiple Linear Regression, adopting a structured Procurement Selection Decision Matrix and revision of existing duration estimation models were suggested to improve fast track delivery and efficient resource utilization. Factors beyond procurement method that influence project performance require further research. The findings of this research may assist policymakers, procurement agencies, and construction professionals in selecting appropriate procurement methods for future infrastructure projects.

Keywords

Design–Build, Design–Bid–Build, Time Duration Estimate, DoR Guidelines, BTC Modelling, Bridge Construction, Procurement Practices, Construction Management