Nearly three months after President Joe Biden signed a roughly $1.2 trillion infrastructure bill into law, federal transportation officials say much of their work is on hold - stuck in limbo as a result of an unresolved congressional fight over federal spending.

The result is billions of dollars unable to be spent, blunting the immediate impact of one of President Biden's signature accomplishments.

"A significant portion of our highway, transit and safety programs are limited" by caps in the existing federal budget, said Carlos Monje Jr., the Transportation Department's third-highest-ranking official. "Without congressional actions, we aren't going to be able to move on many of the new programs funded in the bill."

Among them is $1.2 billion to help reduce carbon emissions and $1.4 billion to protect roads and bridges against the effects of climate change. And while the Federal Railroad Administration is in line to receive $66 billion in the next five years, Monje said the agency can't hire the staff it needs to manage the significant infusion of money.

Some states, meanwhile, are putting off projects until Congress approves $9 billion in additional highway money.

The issues stem from what Monje called a "wonderful dance" between lawmakers who authorize federal spending and those who appropriate the money. The infrastructure bill authorized the money to be spent, but in many cases, it still needs a second round of approval in the form of an appropriation. Congress hasn't been able to agree on spending for the budget year that began in October, and instead has been rolling forward last year's appropriations. That approach does not include the increase in transportation spending.

The Transportation Department's budget is not being held up over any dispute tied to the agency's funding, and with promised money on hold, frustration is rising among lawmakers who helped shape the infrastructure package, federal officials and groups representing segments of the transportation industry. A Friday bridge collapse in Pittsburgh served to heighten the urgency of restoring the nation's infrastructure.

The delay, a coalition of more than 60 transportation industry groups wrote to congressional leaders Monday, is "wholly unacceptable and will cause significant project disruptions, reduced construction and manufacturing employment, and delays in delivering critical transportation infrastructure improvements - just when Americans were promised the most ambitious infrastructure package of our time."

There is a race against the clock on Capitol Hill because the existing federal spending agreement is set to expire Feb. 18. By that point, lawmakers must pass another short-term measure, known as a continuing resolution, or come to a deal on a larger plan. If they don't, the U.S. government - public-works projects and all - would come to a halt.

Democrats and Republicans in the House and Senate began talks at the end of last year, hoping to finance federal operations perhaps until the end of the fiscal year, which concludes Sept. 30. Both sides have expressed a desire to reach a deal and avert a showdown.

Yet lawmakers long have been divided over the specifics of the budget. Democrats hope to approve massive boosts to federal domestic agencies, no longer capped by a law that limited such spending for a decade. To that end, Rep. Rosa DeLauro. D-Conn., the House's top appropriator, led her party toward approving about a dozen spending bills that financed Biden's proposals to expand federal health care, education and science programs.

But the appropriations process became bogged down in the evenly divided Senate. Republicans, led by Sen. Richard Shelby, R-Ala., have rejected the scope of Democrats' spending plans, opposed some of Democrats' policy priorities and sought, instead, to boost the budget at the Pentagon.

Talks between the two sides have continued into this year, according to congressional aides, who in recent days have expressed optimism about a deal. Absent an agreement, Congress would need to adopt another short-term measure - further delaying parts of the infrastructure law.

Rep. David Price, D-N.C., the top Democrat on the House's transportation-focused appropriations committee, said the effects of the delay have been "significant."

"The infrastructure initiative is greatly hampered by the failure to pass a regular appropriations bill," he said.

A top aide to Sen. Patrick J. Leahy, D-Vt., the leader of the Senate Appropriations Committee, pointed to the potential for disruption as the reason the senator has been seeking a full-year budget since May. The official, who spoke on the condition of anonymity to describe the panel's discussions, said Leahy hopes to strike a deal by Feb. 18 so infrastructure work can move forward.

Given the political stakes, transportation industry leaders say it's a matter of when, not if, a deal will be reached and money will flow.

Jim Tymon, executive director of the American Association of State Highway and Transportation Officials, said inaction hurts what should be one of Congress's and the Biden administration's signature accomplishments.

"If they're not able to make good on the promises ... then that no longer is an accomplishment," he said.

If lawmakers can't agree on a year of spending, transportation groups are urging Congress to include special provisions to unlock the infrastructure money as part of any short-term deal.

Mollie Timmons, a spokeswoman for Sen. Rob Portman, R-Ohio, one of the leaders of a group of senators who crafted the infrastructure deal, said he was continuing to work with colleagues "since completion of the appropriations process is critical in order to fully implement the infrastructure law."

But Rep. Peter A. DeFazio, chairman of the House Transportation Committee, laid blame for the holdup on Republicans, noting that only 13 GOP members in the House backed the bill.

For Democratic congressional leaders and the White House, the situation is a delicate one. Monje, who spoke at a virtual meeting to relaunch a left-leaning future-of-transportation caucus in the House, said officials have not spoken much in public about the challenges.

"We have the Congress and we have the presidency," he said. "And so this is our challenge to work together on."

The infrastructure bill draws on several sources of funding for transportation. In an unusual step, lawmakers appropriated billions of dollars upfront, allowing the administration to begin work on some of the signature programs in the law. That includes a $27 billion investment in bridges that Biden announced this month.

Asked about the constraints Thursday as he announced new road safety initiatives that will be bolstered by money in the package, Transportation Secretary Pete Buttigieg there was still much his department is moving forward on.

"Every operation of government, including ours, does best, of course, when we have the certainty of a full budget and normal appropriations," he said. "But I can also tell you there is so much going on and so much on our plate right now that we are keeping very busy delivering on the resources that are actionable in the moment."

But many programs still require the second round of approval. The infrastructure law pumped $118 billion into the Highway Trust Fund, which can no longer cover expenses from gas tax revenue. That money is ready to be spent, but under the terms of the continuing resolution, it is available only at levels that have been rolled forward from 2020 - a gap of about $9 billion this year for roads and $3 billion for transit.

Tymon said that means some state transportation departments, which are responsible for determining how much of the money is spent, are delaying plans at a time when they could have been seeking bids on projects. That translates into construction firms hiring more slowly and putting off other investments.

"This time of year is when state DOTs are laying the foundation to be able to put shovels in the ground," Tymon said. "With the uncertainty at the federal level, it's really causing some states to have to push that schedule back."

At a meeting of the Transportation Research Board this month, the heads of federal highway, railroad and transit agencies said they were limited in what they could do until a full year of appropriations is in place.

Like state transportation departments, Ward McCarragher, vice president for government affairs and advocacy at the American Public Transportation Association, said transit agencies are in a wait-and-see mode as the construction season looms, reluctant to finalize plans.

"These are public entities that are very conservative in their approach," he said.

The programs affected most are those that weren't provided with money upfront and aren't included in the existing budget. That includes funds for some of the administration's top priorities on the environment, safety and racial justice.

“A lot of people have been celebrating the fact that this bill is going to make real progress in addressing climate change, yet we’re not able to move forward,” Tymon said.