The Trump administration promises to pump $1 trillion into improving the country’s crumbling infrastructure, but a benchmark report says it will take almost $4.6 trillion over the next eight years to bring all those systems up to an acceptable standard.

The price tag for redemption has grown steadily for 15 years while an expanding country has focused on building new infrastructure rather than maintaining existing systems that were nearing the end of their natural life.

Since 2001, the cost of repairing those systems has mushroomed from $1.3 trillion to the current figure, more than three times as high, according to an assessment released Thursday by the American Society of Civil Engineers (ASCE). The report comes out every four years.

It gave the U.S. infrastructure an overall grade of D-plus, the same grade it received in 2013, “suggesting only incremental progress was made over the last four years.”

“President Trump is on to something when he calls for a national rebuilding,” ASCE President Norma Jean Mattei said in presenting the study. “But Congress and the American people have to pay for it.”

She said lawmakers should raise the federal gas tax by 25 cents and index it to inflation.

Trump reiterated campaign promises on infrastructure in his inaugural address and in his recent address to Congress, but the only supporting detail for that pledge thus far has been an 11-page white paper issued in October. In that document, Trump said the money would be raised by granting private investors an 82 percent tax credit that would encourage them to pump money into infrastructure projects.

[Trump promised $1 trillion for roads, bridges. The trick is finding the cash.]

“We can use private financing for the major things, but it’s a slice of investment,” said former Pennsylvania governor Ed Rendell (D), who now co-chairs the advocacy group Building America’s Future. “You can’t do it on the cheap. It’s time for Congress to suck it up and vote for real [federal] investment.”

Rendell said the “fix it first” approach that Trump espouses — repairing needy infrastructure before launching new projects — is not likely to draw private investors.

Congressional leaders and state and local officials have made clear that while private investors might put money into select projects in urban areas from which they can expect a return, they would shy away from investment in rural areas and would rather build new infrastructure than repair systems that have deteriorated.

“I think the federal government has to play a larger role,” said Connecticut Gov. Dan Malloy (D).

Infrastructure underpins everyday life in the United States, covering far more than the roads and bridges commonly thought of when the word comes to mind. It includes a vast network of other systems that most people take for granted, including drinking water and sewer service, the delivery of electricity, as well as railroads, transit systems and ports.

The ASCE has been chronicling the decline of infrastructure category by category since 1998, when it took over the task that had been handled for a decade by the National Council on Public Works Improvement.

In recent years, most of the 14 categories the ASCE has assessed have received a D, and hardly any has moved by more than a fraction of a grade. For example, inland waterways were judged to improve from a D-minus to a D, while transit systems declined from a grade of D to a D-minus.

The commentary provided with each grade was revealing:

Airports (D): Congestion at airports is growing, with 24 of the big airports expected to achieve “Thanksgiving-peak traffic volume” at least one day each week.

Bridges (C-plus): Four in 10 of the country’s 614,387 bridges are more than 50 years old and near the end of their designed life span. Nearly 59,000 are structurally deficient.

[Nearly 59,000 bridges in U.S. are structurally deficient]

Dams (D): An estimated 2,170 of the country’s 90,580 dams are considered as “high-hazard potential” because of failed upkeep.

Drinking water (D): There are 240,000 water-main breaks each year, wasting 2 trillion gallons of water.

Electricity (D-plus): Most electrical transmission lines were built in the 1950s and 1960s with a 50-year life expectancy, and they are running at maximum capacity everywhere but Alaska and Hawaii.

Ports (C-plus): Mega-ships now arriving from the Far East and able to transit the newly expanded Panama Canal can call on very few of the 926 U.S. ports unless channels are dredged to accommodate their deeper drafts.

Railroads (B): The private freight railroads that own most U.S. rail track invested $27.1 billion to upgrade systems in 2015 and continue that investment.

Roads (D): Traffic backups cost $160 billion in wasted time and fuel in 2014, and about 20 percent of highway pavement is in poor condition.

Transit systems (D-minus): Though they carried 10.5 billion trips in 2015, chronic underfunding and aging infrastructure have led to a $90 billion repair bill.

ASCE Executive Director Thomas W. Smith III cited an urgent need for the White House to deliver a comprehensive plan for infrastructure restoration.

“Our nation’s infrastructure is making headlines for all the wrong reasons,” Smith said. “While we haven’t seen action [from the White House], we have to hold feet to the fire.”