U.S. drivers traveled a record more than 3 trillion miles on the nation's roads and highways in 2015, according to statistics from the Department of Transportation.
The agency said Monday it has calculated there were 3.148 trillion miles traveled between January and December of last year. The DOT said the previous record was 3.003 trillion miles traveled in 2007.
The transportation department said the figures demonstrate the need for continued investment in the nation's infrastructure.
"Our current infrastructure has ever increasing demands on it, and investments are needed in both the short and long term. Increased gridlock nationwide can be expected unless these investments are made.
The last mileage figures confirmed an earlier estimate from the transportation department that said that the number of vehicle miles traveled would top 3.1 trillion based on totals that were calculated between January and November.
The number of miles that are traveled on U.S. roads is closely watched because states are beginning to test taxing drivers based on how many miles they travel, instead of how many gallons of gas they buy.
The plan, known in transportation circles as Vehicle Miles Traveled (VMT), faces opposition in Washington, where it has been floated as an alternative to the 18.4 cents per gallon gas tax that is currently used to pay for infrastructure projects.
But Oregon and California are moving ahead with pilot mileage fee programs, and transportation advocates in Washington have suggested moving to a national mileage-based fee system as receipts from the gas tax have dwindled in recent years. But the push has little support in Congress.
The Transportation Department has said that the data on the number of miles that are traveled could be used to inform decisions about future transportation projects, even if Congress does not switch to a mileage fee taxation system to pay for the nation's roads.
"The data from 2015 reaffirm the growing demands challenging the nation’s roads and underscore the value of the recently enacted FAST Act, which will invest $305 billion in America’s surface transportation infrastructure — including $226 billion for roads and bridges — over the next five years," the agency wrote in a recent blog post.
"These new figures confirm the trends identified in our Beyond Traffic report, which projects a 43 percent increase in commercial truck shipments and population growth of 70 million by 2045," the blog post continued. "So, even though we have seen indications that individuals might be driving fewer miles per person, an increasing population with increasing freight demands still leads to more and more total miles traveled and more challenges on the road ahead."
The normal source for transportation projects is revenue collected by the federal gas tax. The tax has not been increased since 1993, however, and the pace of infrastructure expenses is outpacing it, as cars become more fuel efficient.
The federal government typically spends approximately $50 billion per year in road and transit spending, but the gas tax only brings in about $34 billion per year.
The $305 billion transportation bill approved by Congress last year included a package of offsets from other areas of the federal budget that totaled about $70 billion to close the gap long enough to pay for five years' worth of highway and transit projects.
Transportation advocates have suggested a switch to a mileage-based program as an alternative to raising the gas tax, but critics have raised concerns about government officials tracking the movements of drivers.
The Obama administration and Republicans in Congress have in the past distanced themselves from both mileage-based driver fees and an increase in the gas tax. The president and lawmakers have instead talked up using revenue from taxing corporate profits that are stored overseas to pay for roads.
The 2015 highway bill includes a grant program known as the Surface Transportation System Funding Alternatives that provides $95 million to help states like California study alternatives to dwindling gas tax revenues.
Prior to passing the highway bill, Congress had not passed a transportation funding package that lasted longer than two years since 2005, much to the chagrin of infrastructure advocates in Washington.
The transportation department has said the 2015 mileage total shows that the nation can ill-afford future highway bill delays.
"No matter how you slice it, that's a lot of miles ... in terms of absolute value, and also as an indicator of what kind of volume America's roads are bearing," the agency wrote in a January blog post.
"Because each of those miles is wear and tear on the roadway surface. And when combined, those miles represent a significant challenge to our capacity. And that means traffic congestion. Which means lost time, lost money, and increased greenhouse gas emissions," the blog post continued. "So, while we appreciate that our roads made possible those 3+ trillion vehicle miles traveled, we aren't exactly celebrating this new record."