This chapter first discusses the work done in the past on the effect of tunnel length, tunnel diameter, geology, type of tunnel, and environment on the construction cost. The scatter between dependent and independent variables shows the complexity of predicting the tunnel construction cost and the choice between conventional and mechanized tunneling methods. A comparative cost analysis is made for drill and blast and mechanized tunnelling methods for a given geology and tunnel diameter to make the solution to the problem more comprehensive. The initial cost investment for both methods presented in Chap. 6 is used in the comparative study.