If lawmakers enact the $550 billion bipartisan infrastructure bill now before the House, state and local officials will have to decide which projects to spend money on. But researchers have found that transportation planners frequently expect more people to use their road and transit projects than ultimately do so. Yet those optimistic forecasts become part of the justification for spending millions or billions of dollars on such projects.
"The implication is rather stark: It’s wasting resources," said Robert Bain, a traffic consultant who has studied toll-road forecasts. "We may be focusing resources and focusing investment in areas that are not as productive as other ones."
The infrastructure bill includes a provision requiring the U.S. Transportation Department to assess travel forecasts’ accuracy and to help state and local governments come up with better models.
Compounding their challenge is the Covid-19 pandemic, which has changed commuting habits and clouded expectations for how people will travel in the future.
Many workers have spent more than a year working remotely at least part of the time, and it isn’t clear when or whether they’ll return to their old patterns, making future demand for roads, buses, subways, airports and other infrastructure difficult to gauge.
"What we need to demonstrate to the decision makers is that we’re helping them make good decisions and giving them good answers and good numbers," said Dave Schmitt, a travel forecaster with Connetics Transportation Group, a consulting firm. "The big wrinkle is Covid."
A Federal Transit Administration survey of 27 recent public-transit projects that opened between 2007 and 2015 found that the average one overestimated ridership by about 21% two years after opening. That was an improvement over previous years. Projects that opened between 1990 and 2002 overestimated ridership by an average 77%, the FTA found.
"There’s an enormous temptation to use ridership projections to present the project in the best possible light," said Carole Voulgaris, a professor of urban planning at Harvard University.
Before the pandemic, ridership of an extension of the Washington, D.C., region’s subway system that opened in 2014 was roughly half of what had been forecast before it opened, according to the FTA. Those forecasts were completed before the 2007-09 recession, which limited development and population growth along the route, the agency said.
Public road projects overestimated use by about 6%, according to a study of roughly 1,300 projects by the National Academies of Sciences, Engineering and Medicine that was conducted before the pandemic. And traffic counts on a sample of toll roads around the world were roughly 77% of what had been forecast, according to Mr. Bain’s research.
"This is probably one of the biggest failures of the industry, and not just in the U.S. It’s an international issue," he said.
The prospect of a windfall in new money from the infrastructure bill "very much highlights that we need to get it correct," said Gregory Erhardt, an engineering professor at the University of Kentucky and an author of the National Academies report.
"There is some incentive for forecasts to be high if they make [a project] more likely to get built," he said. "If we were to systematically evaluate every forecast we do and issue a report and say, ‘This is how accurate we were after the fact,’ it takes away that incentive."
To produce a forecast, planners look at an area’s population predictions and employment figures as well as the number of cars and licensed drivers in each household. They study existing roads and transit networks and estimate how often and how far people go when they commute to work or make other trips.
A big unknown in any travel forecast is how the economy will evolve. A recession can sharply reduce the number of trips people make if they no longer have jobs. That, in turn, can contribute to inaccuracies in travel forecasts.
"Whatever the economic conditions were when the model was calibrated, we assume that those economic conditions hold true," said Mr. Schmitt, who also co-wrote the National Academies study.
In some cases, the forecasts can be controversial. In Ohio, for instance, the state’s transportation officials plan to widen 9 miles of I-77 near Akron from four lanes to six at a cost of $125 million. At one point on the stretch, the department sees average traffic rising to 71,890 vehicles a day in 2040 from 66,093 in 2019, the last year before the pandemic, according to a 2016 forecast. At another point, the agency forecasts traffic reaching 63,360, up from 52,366.
Matt Bruning, a spokesman for the Ohio Department of Transportation, said the forecasts account for future residential and commercial development in the area.
"Because of Ohio’s location within a day’s drive of 60% of the U.S. and Canadian population, we continue to see a steady increase in freight traffic," he said.
Jason Segedy, planning director for the city of Akron, questioned those figures.
"I’m fairly skeptical that the projections that are being made now are going to come to pass," he said. "I think the state still often relies on travel models that forecast that there’s going to be continued growth in traffic."
The Akron metropolitan area lost about 0.14% of its population between 2010 and 2020, according to the Census Bureau.
"Our money could be better spent fixing the roads that we already have, or have the state maybe take a more active role in urban revitalization," Mr. Segedy said.
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