Construction of a bridge in downtown Miami. Credit: CHUYN via istock/Getty Images Plus.

Infrastructure Investment: Appraisal, Biases, and Politics

By José Gómez-Ibáñez, Zhi Liu, Agosto 17, 2022


Given the high cost of infrastructure investments, picking the right projects is important. Three chapters in the Lincoln Institute book Infrastructure Economics and Policy: International Perspectives describe how cost-benefit analysis has come to be almost universally applied by governments and international financial institutions for evaluating infrastructure projects, despite some notable limitations—and how investment decisions are affected by biases and politics. 

The Development of Cost-Benefit Analysis 

Don Pickrell, chief economist at the U.S. Department of Transportation’s Volpe National Transportation Systems Center, describes the evolution and methodological challenges of cost-benefit analysis in a chapter on economic evaluation. As he explains, a mid-nineteenth-century French engineer, Jules Dupuit, is widely credited as the originator of cost-benefit analysis. Dupuit’s main concern was to determine whether the investment in a new infrastructure facility, such as a bridge, was worthwhile; he proposed that the test should be whether the benefits to the bridge’s direct users—for example, savings in time, labor, fuel, and other areas—exceeded the cost of building and maintaining the bridge. 

This focus on direct user benefits has long been criticized by some for ignoring the wider economic impacts of infrastructure. Proponents of the wider impact approach argue that the time savings and other benefits to direct users may be passed on to downstream firms, allowing them to implement further productivity improvements. They argue that ignoring these impacts will understate the benefits of the project to society as a whole. Pickrell explains that over the years, researchers have attempted to measure these wider economic impacts by building models of the entire economy that include estimates of the effects of changes in the productivity of infrastructure on the productivity of other sectors  

This approach—building models to estimate both the direct and wider economic impacts of a project—did not prove popular with researchers or governments until the last decade, when several researchers returned to the topic. Pickrell speculates that the use of these economy-wide models was discouraged in part by the need to estimate, or assume, so many parameters. The models are also less suitable for choosing from a number of individual infrastructure projects—the task officials were typically charged with—than for evaluating economy-wide reforms. 

Skeptics of the approach also argued that the wider economic impacts identified were often not new and additional impacts, but rather transfers of impacts from the direct users to other parties. The opening of a new bridge, for example, usually stimulates an uptick in property values and the construction of new housing or other developments nearby. Land values and housing increase primarily because the bridge makes travel faster; to count the property value or new housing as benefits along with the travel time savings to the direct users would be to count the same benefit twice. 

In practice, a consensus has emerged that wider economic impacts can be included without double-counting if they involve the correction of inefficiencies in the affected downstream markets. Examples include environmental costs and benefits imposed on third parties, the general improvements in productivity caused by the growth of urban agglomerations, or reductions in prices caused by an increase in competition from the breakup of a monopoly.  

The development of cost-benefit analysis into a tool used almost universally by governments and international financial institutions to evaluate major public infrastructure projects is remarkable. The practice has been encouraged in large part, Pickrell explains, because it has become increasingly sophisticated over the last century.  

Despite the value of cost-benefit analysis, the relatively few studies of its influence on the actual choices of government produced discouraging results: the highest-ranked projects are rarely selected, the research shows. Defenders of cost-benefit analysis argue, however, that the real advantage of this approach is unlikely to be the selection of the best project over the second-best alternative, but rather the elimination of some of the worst from consideration. 

Optimism Bias 

Cost-benefit analysis is not perfect. A careful analysis in chapter 7 by Professor Bent Flyvbjerg of Oxford University and statistician Dirk Bester reveals overwhelming statistical evidence that costs tend to be strongly underestimated, while benefits are strongly overestimated. Their amazing dataset includes 2,062 infrastructure projects representing six investment types in 104 developed and developing countries, which were put in service between 1927 and 2011. 

Forecasting errors are often blamed on proximate changes in project design or environment, such as unforeseen increases in scope or complexity, higher than expected inflation, lower than expected competition, and various similar factors. But Flyvbjerg and Bester argue that the root causes of the errors are well-known behavioral limitations, especially optimism bias and overconfidence bias. This observation suggests that improving forecasting will be difficult because the problems are so deeply ingrained in human nature. Flyvbjerg and Bester make specific recommendations for reforming cost-benefit analysis, such as debiasing and giving consultants a financial stake in the accuracy of their forecasts. 

Politics of Excess or Shortfall 

In chapter 8, John Donahue of Harvard’s Kennedy School describes the political forces that lead to excesses or shortfalls of public spending for infrastructure. Donahue explores the school of public choice economics, whose theoreticians assume that individuals rationally pursue their self-interest in a democratic society governed by voting rules of various kinds. 

Not surprisingly, the answer to the question of whether this pursuit will result in excess or shortfall depends on one’s assumptions about how well informed the voters are as well as the voting rules. For example, one famous public choice scholar, Anthony Downs, argues that spending will be less than optimal mostly because voters tend to underestimate benefits more than they underestimate costs. Another scholar, Mancur Olson, argues that spending on public goods is driven by coalitions, which are often most effective when they are small, or when they can devise perks—e.g., roadside assistance from the American Automobile Association—for those who join them. Finally, Gordon Tullock demonstrates how majority voting to determine whether to fund similar projects would lead to overspending, because the proponents of each project have incentives to exchange support with the proponents of the other projects (a practice known as log rolling). 

All three chapters inform the reader about the strengths and weakness of cost-benefit analysis, the existence of optimism biases driven by human nature, and how public choices influence the level of public spending for infrastructure. Knowing more about these factors can help improve decision making for public infrastructure investments. 



José A. Gómez-Ibáñez is the Derek C. Bok Professor Emeritus of Urban Planning and Public Policy at Harvard University. Zhi Liu is senior fellow and director of China Program at the Lincoln Institute of Land Policy. They are the editors of Infrastructure Economics and Policy: International Perspectives

Image: Construction of a bridge in downtown Miami. Credit: CHUYN via istock/Getty Images Plus.