As House Democrats prepare to bring back earmarks, billions of dollars tagged for lawmakers’ favored transportation projects before a decade-old ban sits unspent.

Federal Highway Administration records show that as of October 2019, about $2.4 billion in 3,600 earmarks at least 10 years old had yet to be fully spent. Of those, about 300 earmarks worth about $400 million had never been tapped, according to the records.

Supporters of earmarks — pots of money enshrined in law and directed to particular projects — say they are a mechanism for lawmakers to direct money to worthy causes in their districts while helping to build support for infrastructure legislation.

But state transportation officials, who are responsible for spending almost all federal highway funds, point to the unspent money as an example of the system’s inefficiencies, tying up resources they otherwise would have used long ago.

On Wednesday, Rep. Peter A. DeFazio (D-Ore.), chairman of the House Transportation Committee, announced he would allow earmarks in a forthcoming infrastructure funding bill.

“The discretion to fund projects should not be reserved for State or Federal bureaucrats,” DeFazio said in a statement. “Elected representatives know the infrastructure needs of their district and should be allowed to identify projects and advocate on behalf of their constituents in legislation.”

DeFazio’s office set out a process for requesting earmarks designed to ensure projects have backing from local and state governments and sufficient sources of other funding. The move follows a similar announcement Friday by Rep. Rosa L. DeLauro (D-Conn.), chairwoman of the House Appropriations Committee.

Democratic leaders in the Senate have yet to say whether they will follow suit.

Before a ban on earmarks was imposed in 2011, state officials say the amount of earmarked money often was too small to jump-start a project, or was put into the hands of local agencies that didn’t know how to properly spend it. And unlike other federal transportation funding that has to be prioritized in multiyear plans and spent within four years, earmarked money typically doesn’t expire.

Congress recognized the problem in 2015, passing a provision that allows dormant earmarks more than a decade old to be reused on other nearby projects. States have used that process 3,000 times, shaking loose $2.2 billion.

The highway administration annually publishes new lists showing hundreds of millions of dollars in idle funds.

The 2019 records, the most recent the highway administration has compiled, include $13 million for an interchange in Massachusetts, $22 million for a road in Georgia and $21 million for a Nevada bridge.

Last week, before Democrats had confirmed their plans, state officials gathered virtually to discuss the return of earmarks. Susan Howard, program director for finance at the American Association of State Highway and Transportation Officials, called earmarking “disruptive and detrimental” before posing the question: “How can the process be structured to help or at least do no harm to state DOTs?”

Earmarks were a feature of federal spending bills for decades, but their use exploded in the late 1990s. Jeff Davis, a senior fellow at the Eno Center for Transportation, attributed the growth to the availability of spreadsheets that made it easier to track thousands of separate pots of money.

Defense projects accounted for the lion’s share, followed by transportation. A five-year transportation bill passed in 1987 included 152 earmark projects, drawing President Ronald Reagan’s veto as he complained about “lard.”

But Congress overrode the veto and the use of earmarks grew: The 2005 version of the bill featured 5,671 of them.

By 2006, the Transportation Department’s inspector general calculated that earmarked funds accounted for 13 percent of the department’s budget. Because they often went to projects that agency officials scored poorly, the watchdog said they “may not be the most effective or efficient use of funds.”

Highway administration records include earmarks as small as a few thousand dollars. In some cases, the earmarked money was dwarfed by the size of a project it was attached to. Nick Donahue, Virginia’s deputy transportation secretary, described a $20 million earmark for a multibillion-dollar project.

“That clearly I don’t think is a great outcome because the money sits there and we couldn’t move forward just because of the higher cost of the project despite having the earmark in hand,” he said.

After years of trying to tighten up rules and impose transparency, congressional leaders imposed a moratorium on earmarks following an FBI corruption investigation, as well as scrutiny of seemingly wasteful projects such as the Bridge to Nowhere in Alaska.

Some earmarks from the 2005 law are among those that highway administration data lists as unused. One of the largest is $16 million for a highway project in Bartow County, Ga., known at the time as the U.S. 411 Connector.

When the House adopted the 2005 transportation budget bill, then-Rep. Phil Gingrey (R-Ga.) touted the money as “a huge step.” But 16 years later, work on the project has yet to begin in earnest. In 2019, officials told local residents they hoped to finish by 2030.

Peter Olson, the county administrator in Bartow County, said the project will be valuable once complete, helping to connect industrial areas and ease congestion.

Although earmarks might sit untouched, money sometimes can be used for its original purpose. Earmarked funds for the Massachusetts interchange have been tapped and a preconstruction conference is scheduled for this month, said Kristen Pennucci, a spokeswoman for the state transportation department.

Dan Kulin, a spokesman for Clark County, Nev., said bidding for the construction of the Nevada bridge opens next week.

Democrats who control the House say they will set limits on the practice, including banning earmarked funding for private businesses. The Appropriations Committee funds will be disclosed before becoming law and each member will be allowed to make 10 requests.

The Transportation Committee will require members to show they have support from state departments of transportation or local agencies. Lawmakers also will be encouraged to submit requests that further environmental and racial justice goals.