Combining <i>Ex Post</i> Quantitative Metrics and Case Narratives to Reveal Factors Affecting Cost and Economic Development Outcomes of Transportation Investment Projects in the United States

Whereas some transportation projects are primarily intended to address congestion and capacity needs, others are designed to expand access and enable economic development in target areas. For this latter group, cost-effectiveness depends on achieving desired and predicted costs, access improvements, and economic development outcomes—factors heavily influenced by setting accurate preproject expectations and successfully managing public review and implementation processes. This article demonstrates how the publicly available U.S. national ex post project database of highway and transit projects can be used to (a) evaluate the extent to which intended and anticipated outcomes are realized, and (b) identify planning factors that contribute to under- or overachievement of these results. Using a structured methodology that integrates quantitative pre–post metrics with detailed case narratives, this research illustrates the range of economic development impacts associated with different project types, locations, and supportive planning contexts. These findings underscore the need for multiphase or longitudinal evaluation frameworks when evaluating cost management and the economic benefits for major transportation projects, to fully capture changes in project scope and objectives over time, and account for diverse impact areas and time frames. Ultimately, this research makes a case for the broader adoption of systematic ex post analysis in transportation planning, and shows how this information can be used to better inform public discussion and enhance the accuracy and effectiveness of future infrastructure investments.