Early cost estimation models based on multiple regression analysis for road and railway tunnel projects

Abstract

Estimates of a tunnel construction cost are among the most critical tasks during the planning stage of both road and railway projects to justify the project and allow a valid comparison between alternative solutions and perform reliable “what if” scenarios relative to the tunnel diameter and length. Numerous factors influence the tunnel construction cost, and very little information on these factors is available at the early stage of project planning. Developing an accurate cost estimate is therefore very difficult at this stage, and thus, a very limited number of cost models are available for this purpose. This paper develops early parametric cost estimating models for road and railway tunnels in the planning stage of a project based upon the application of multiple regression analysis on 25 constructed projects located in Western European countries. The developed models incorporate not only tunnel length and diameter but also the type of tunneling methods (mechanized and conventional), which are largely affected by geological conditions. The results showed high correlation coefficients (R²) of 0.968 and 0.79 for mechanized and conventional tunneling models respectively. In addition, the results of the developed models were compared against actual costs to assess their accuracy and robustness. The developed models achieved cost estimation accuracy over 75%, indicating that the models fit for their purpose and lead to fairly accurate cost estimates of road and railway tunnels.