Addressing the chronic underestimation of capital and operating costs in urban transportation projects, this book provides a detailed analysis of the cost estimating process using case studies from three US cities and outlines a practical framework for this process. The work goes beyond a simple quantitative approach to explaining cost underestimation and looks at the planning process as a tool for both argumentation and structuring the argumentation. This approach highlights the difficulties in several components of the estimating process and suggests specific and practical actions to address these problems. The proposed framework will strengthen the estimating function and the link between analysis and decision in urban transportation planning.