An earlier version of this story misstated the rate at which drivers’ licenses were declining for males. It has been corrected.

Millennials have received a bad rap for everything from selfishness to technology addiction. Now they can add failing infrastructure to that list.

Millennial driving and vehicle purchasing habits—or lack thereof—greatly contribute to the decreased collection of the federal highway gas tax, which is used to fund transportation and water infrastructure projects, according to a report released Monday by Standard & Poor’s Ratings Services. “There’s been a pullback in vehicle miles traveled, and much more so among the younger generation,” says Beth Ann Bovino, U.S. chief economist for S&P. “It probably will continue if you look at the number of driver’s licenses being issued. The younger population isn’t commuting by car.”

The number of males between the ages of 16 and 28 with drivers’ licenses declined to 80% in 2009 from 86% in 2001, according to the report. Licensing rates for females in the same age group remained stable at 82%, though Bovino says the overall rates are likely to decline further over time. And while the national average of vehicle miles traveled has remained relatively stable since 2002, public transportation ridership increased 36% between 1996 and 2014.

Despite the growing preference for public transportation, millennials are still buying cars, but prefer fuel-efficient vehicles. The report states that young households account for a significant amount of overall car sales—one of every four cars sold in the U.S. so far this year—though most of them were compact vehicles, according to data from vehicle market research company J.D. Power. Millennial buyers made up 30% of compact car sales and 25% of small car sales between 2010 and 2014. Fuel-efficient cars do little to ease the strain on funds collected via gas taxes.

However, their environmental and financial benefits may outweigh the decrease in tax revenue. Vehicles with improved fuel efficiency conserve oil, reduce carbon pollution and save drivers money on fuel costs, according to the EPA.

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And the proportion of environmentally friendly cars sold isn’t likely to change, either. The Environmental Protection Agency is requiring that all passenger cars, light-duty trucks and medium-duty passenger vehicles achieve a fuel efficiency of 54.5 miles per gallon by model year 2025.

As a result of decreased reliance on gasoline, Bovino says that public spending on infrastructure for transportation and water has dropped about 20% from 1996 to 2013. “State and local governments are kind of in a bind,” she says. “States are either canceling projects or have to turn to the bond market.” “Getting more mileage per gallon is a good thing,” Bovino says. “The question is if the gas tax, as created, might not fit current needs.”

Not everyone blames millennials. The increased number of miles traveled between gas station fill-ups has been a major problem for funding, says Doug Hecox, a spokesman for the Federal Highway Administration, but the agency hasn’t associated the problem with millennial consumer behavior. “The Highway Trust Fund has been starving because of improved fuel economy,” Hecox says.

The most effective solution to infrastructure funding would come from Congress, Bovino says, but due to its current deadlock, states have been left to figure out funding strategies on their own, with little success. The Massachusetts state government attempted to raise the gas tax in a 2013 transportation law, but the measure was thrown out the following year by voter referendum.

“It’s not just the younger generation that’s driving less, it’s just more so true for the younger population,” Bovino says. “If this is the road that transportation is heading down, then it seems like regulation needs to catch up.”