Cars drive past construction workers along Interstate Highway 66 in Manassas, Virginia, on August 10, 2021. (Photo Credit: Andrew Caballero-Reynolds/AFP/Getty Images via CNN Newsource)

(CNN) — In the past four years, America’s infrastructure has improved — but just slightly.

A report card released Tuesday by the American Society of Civil Engineers (ASCE) gave the United States an overall grade of C, up from a C- in 2021 and consistent D-ranged grades since the start of testing in 1998.

The ASCE, a 172-year-old group headquartered in Reston, Virginia, examined the conditions of 18 categories such as aviation, bridges, drinking water, public parks, solid waste management and wastewater treatment. The highest grade went to ports, which received a B, while the lowest grade was a D for stormwater utilities and public transit.

An A means “facilities meet modern standards for functionality,” while an F means “in unacceptable condition, with widespread, advanced signs of deterioration,” according to the ASCE.

The ASCE credited improvements made in the last four years to the $1.2 trillion Infrastructure Investment and Jobs Act passed in 2021, which allocates $550 billion over five years to systems including bridges, roads, broadband, water and energy.

“The key is to build on the momentum that we have now. It’s easy to talk about the benefits of infrastructure investment,” Darren Olson, ASCE’s committee chair for the 2025 report, said Monday in a press briefing.

But the United States still faces “a substantial investment gap,” the report noted, and “projects should be modernized or replaced by prioritizing resilience to withstand extreme weather.”

Poor infrastructure costs American households $2,700 a year, Olson said. If current infrastructure funding continues, it could save Americans about $700, he added.

Broadband was added to the 2025 report, adding a category since the 2021 report. Eight of the categories, such as dams, hazardous waste, levees and inland waterways, improved their ratings over the last four years. Nine categories received a D-range grade, down from 11 in 2021.

Two categories saw their grades dip. Energy and rail, which received a D+ and B-, respectively, were downgraded because of “concerns related to capacity, future needs and safety.” The ASCE noted energy concerns because of increased interest in electric vehicles and the influx of data centers, many of which are used for artificial intelligence, will demand 35 gigawatts by 2030.

Passenger rail, such as Amtrak, will need more funding to expand and meet safety requirements as ridership increases, said Kristina Swallow, a current member and former president of ASCE.

An estimated $9.1 trillion would be needed to ensure all 18 categories reach “a state of good repair,” the ASCE noted. In a 2024 report, the ASCE estimated only $5.4 trillion in public and private investments will be made through 2033 if recent congressional funding levels continue, which leaves a $3.7 trillion gap — up from $2.95 trillion estimated in 2021.

Roads ($2.23 trillion), energy ($1.88 trillion) and schools ($1.1 trillion) would need the most funding, according to ASCE’s report.

“This investment is necessary in order to continue to strengthen our nation. It’s a way to bring home-grown jobs and delaying investment in our infrastructure is delaying our well-being,” said ASCE President Feniosky Peña-Mora.

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