President Biden’s infrastructure plan calls for the federal government to take on a vast new role in funding the nation’s transportation networks, seeking to rebuild roadways and transit while battling climate change, racial injustice and traffic deaths.

The plan, which Biden formally unveiled Wednesday, calls for dramatic spending increases of $621 billion, part of a $2 trillion overall investment in jobs and infrastructure designed to stretch over eight years, according to White House summary documents. Much of the transportation spending would be over a five-year period, an administration official said.

It calls for $85 billion for transit — doubling existing federal spending — and another $80 billion for rail, which historically has received limited federal aid. The money would expand access to bus service and Amtrak, connecting more cities with the aim of reducing road congestion and driving down greenhouse gas emissions.

At the same time, Biden is proposing spending $115 billion to repair about 20,000 miles of roads and 10,000 bridges. The plan emphasizes repairing roads, rather than expanding them.

“These are investments we have to make,” Biden said Wednesday in Pittsburgh. “We can’t afford not to.”

The administration is calling for the money to be layered on top of existing federal spending on roads and transit, which at current levels is about $300 billion over five years. That would equate to $365 billion in highway spending, $189 billion for transit and $94 billion for rail over five years, according to an analysis by Jeff Davis, a senior fellow at the Eno Center for Transportation.

The breadth of the White House plan underscores the scale of challenges facing the nation’s transportation systems and the administration’s willingness to pour federal resources into meeting them. The proposal comes after the federal government took an unprecedented role in funding transportation amid the coronavirus pandemic, pumping tens of billions of dollars into transit agencies and funding airline payrolls.

Yonah Freemark, a senior research associate at the Urban Institute, a left-leaning economic and social policy think tank, said the proposal is the first of its kind to put the environment at its core while emphasizing transit and rail.

“That policy is a dramatic change from the way we have typically invested in surface transportation in the United States,” Freemark said.

Democrats in Congress, who have proposed their own ambitious transportation plans in recent years, generally were enthusiastic about the proposals. But Republicans questioned some aspects, as well as the tax increases proposed to pay for it.

Rep. Sam Graves (Mo.), the top Republican on the House Transportation Committee, said Biden’s plan would struggle to win the support of his party.

“The president’s blueprint is a multi-trillion-dollar partisan shopping list of progressive priorities, all broadly categorized as ‘infrastructure’ and paid for with massive, job-killing tax increases,” he said in a statement.

Neil Bradley, executive vice president at the U.S. Chamber of Commerce, called the proposal “dangerously misguided” for its reliance on broad-based tax increases. He said those who use infrastructure projects should foot the bill for them, as the federal government historically has done through gas and diesel taxes.

But speaking Tuesday in Virginia, Transportation Secretary Pete Buttigieg said the nation had a unique opportunity. Communities across the nation stand to benefit, he said, “if we seize the moment that’s upon us, a once­in-a-century alignment of demonstrated need, bipartisan interest, public impatience and, I can tell you, a very supportive president leading the way.”

How the proposal might move through Congress isn’t clear. Democrats could seek to use the budget reconciliation process — which would avoid needing Republican support in the Senate — but that would place sharp limits on policy changes.

The administration has noted a $1 trillion backlog in transportation funding, which the plan, particularly when combined with state and local government spending, could do much to address. Still, the White House estimates the plan itself would offer only enough money to modernize 20,000 of the 173,000 miles of roads Biden has said need repairs.

An administration official said there is no “one-size-fits-all” answer to when projects would get underway, noting that some measures — such as tax incentives — would come most quickly, while others, such as an ambitious bridge overhaul, would take time.

Jim Tymon, executive director of the American Association of State Highway and Transportation Officials, said the plan is encouraging but that much would depend on what is included in normal transportation funding legislation that Congress will consider this year.

“If it’s laid out over multiple years and is done in conjunction with a long-term surface transportation reauthorization bill, this is a way to deal with the infrastructure investment deficit we’ve been facing,” he said.

The administration also is seeking to tackle a legacy of racist transportation planning, calling out Interstate 81 in Syracuse, N.Y., and the Claiborne Expressway in New Orleans — highways that destroyed predominantly Black neighborhoods. The plan calls for a $20 billion program to reconnect neighborhoods broken apart by such projects, as well as $5 billion in tribal transportation and workforce training.

The White House also framed increased spending for transit as a matter of racial equity, saying it is disproportionately used by people of color.

The plan calls for a $174 billion investment in electric-vehicle manufacturing and charging, establishing grants to build charging points and to electrify school and city buses.

It also seeks to address a rise in pedestrian and cyclist deaths in the past decade by dedicating $20 billion to road safety. Among other things, the money would be used to fund Vision Zero plans, designed to guide city and county efforts to eliminate traffic deaths.

Rep. Peter A. DeFazio (D-Ore.), chairman of the House Transportation Committee, helped craft a similar infrastructure proposal that passed the House last year. He praised Biden’s approach Wednesday, saying it moves “our infrastructure out of the 1950s and into the modern era.”