WASHINGTON - Dueling proposals to fund the nation's ailing infrastructure network follow decades of timidity in Washington - a period that has seen roads crumble and a warming climate threaten investments of the past.

A line of presidents couldn't make transformational investments in infrastructure, despite big promises and yawning national needs. For those in the trenches, the question in 2021 is whether the nation still can make good on its aspirations - from upkeep of its physical foundations to meeting the challenges experts say will intensify with a changing planet.

"NASA just landed on Mars and we had a big vaccine," said Costa Samaras, who worked as a transportation engineer in New York City and now studies infrastructure resilience at Carnegie Mellon University. "We can do big things - but we should be doing big things in infrastructure, right?"

Biden and his supporters have echoed those appeals in seeking to build support for a $2.3 trillion infrastructure and jobs proposal, which Republicans have knocked as too sprawling and expensive. Biden also set a goal of halving U.S. greenhouse gas emissions by 2030, work that would be spurred by his infrastructure plan.

But experts say achieving those ambitions would take a level of creativity and perseverance that have failed a generation of leaders in Washington.

Standing at a union shop floor in Pittsburgh to unveil his proposal, Biden invoked the collective accomplishments of the 20th century as a national muse, citing World War II, the build-out of interstate highways and the space race against the Soviets as inspirations for his approach.

He called for modernizing transportation networks while battling climate change through a vast addition of new jobs targeting both priorities. "A blue-collar blueprint to build America," he called in a joint address to Congress.

Republicans have seized on his broad definition of infrastructure - which includes racial justice issues, worker rights and community colleges - to dismiss Biden's plan as a grab bag stuffed with liberal priorities, backed by job-killing tax hikes.

Both parties say they want action on infrastructure. That's where the consensus starts to fray, as it has many times before. Communities across the nation are looking to Washington's leaders, wondering whether the outcome in this time will be different.

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The broader ambitions of Biden's plan reflect those of some local leaders, transportation experts and environmental advocates outside Washington who have spent decades pushing for aggressive action on infrastructure.

After Biden won the election, Pittsburgh joined cities in Ohio, West Virginia and Kentucky in calling for hundreds of billions in federal dollars for electric cars and trucks, efficient buildings, clean energy and job training.

Elsewhere, expansive plans would stretch transit lines through traffic-choked Los Angeles, electrify passenger ferries in Washington state and dig a new train tunnel into Manhattan. A partner in the nation's capital could fuel major accomplishments, advocates say, with some calling it an Eisenhower-esque opportunity.

Transportation experts, mindful of the interstate highway system's launch in the 1950s, are calling for undoing the polluting and community-bulldozing practices of that earlier national push, ideas embraced by Biden and his team.

"It won't have that same kind of concrete quality, so to speak, of something like the interstate highway network," Transportation Secretary Pete Buttigieg said in an interview with The Washington Post. "It's got a different shape because the investments are distributed. So this is often playing out one community at a time."

As the biggest source of U.S. emissions, transportation is at the center of Biden's climate plans. For many, the challenge is clear: how to cut the annual tally of more than 1.9 billion metric tons of emissions from the transportation sector to zero, improving quality of life and helping to stave off severe environmental consequences.

The scope of the endeavor is significant.

Samaras compared the scale of improvements needed to address climate change in the infrastructure realm to the equivalent of building Boston's Big Dig in nearly every American community. That massive and disruptive tunnel-and-bridge project took a quarter-century and cost nearly $15 billion.

Reflecting a view shared by many climate and infrastructure experts, Samaras urged a shift from gasoline and diesel to electric vehicles, and a vast expansion of public transit. He also called for redesigning roads to make them safe for widespread biking and walking. And, he said, that must be done while rejecting racist development practices of the past, such as routing highways through Black neighborhoods.

Biden's plan calls for spending $115 billion to rebuild highways and bridges, reduce congestion and cut emissions, but even more - $174 billion - to spur electric vehicles. Tens of billions more would support clean energy and climate research.

"We're in a crunch here. We've got to reduce emissions and we need to do it quickly," said Robbie Orvis, a modeling expert at San Francisco-based Energy Innovation, which advises policymakers on climate efforts and helps tally the effects of potential policies.

During the campaign, Biden set a goal of reaching net-zero emissions from all sources by 2050, and his targets at an April climate summit would be a major step along that path. His infrastructure plan embraces some of the policies experts say are needed to get there, but do not go far enough to meet the most ambitious goals.

It makes sweeping commitments, promising that "every dollar" spent on rebuilding infrastructure "will be used to prevent, reduce and withstand the impacts of the climate crisis." And 40% of the benefits of that spending will go toward disadvantaged communities, according to his plan.

Although efforts to calculate the effects of Biden's proposed policies are ongoing, Orvis said the president's push for installing 500,000 charging stations, offering rebates for electric vehicles and doubling federal transit investments would cut emissions. But the part of the plan that could have the biggest effect on transportation-related emissions is the proposed clean energy standard, which would require utilities to transition from fossil fuels to clean technologies.

"The more you decarbonize the grid, the more benefit you get from moving to (electric vehicles),"Orvis said. "They're all part of the same story."

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Regardless of efforts to shape emissions, highway construction will be a significant part of any infrastructure package that passes Congress. An existing highway and transit funding bill is set to expire this fall.

Biden has decried research showing 1 in 5 miles of highways and major roads are in poor condition, and he points to tens of thousands of bridges that need work. His plan would modernize 20,000 miles of road, take on 10 of the nation's biggest bridge-reconstruction projects and repair 10,000 smaller bridges.

Republicans say the focus should be on conventional ideas of infrastructure. Dismissing Biden's plan as an "expansion of the welfare state," Senate Republicans offered a $568 billion alternative that prioritizes roads, but also includes spending on broadband and water projects. The Republican plan is hundreds of billions of dollars smaller than Biden's and does not call for raising corporate taxes.

"This needs to be about roads and bridges," Rep. Sam Graves of Missouri, the top Republican on the House Transportation Committee, said at a hearing with Buttigieg. "A transportation bill needs to be a transportation bill," not a catchall or environmental wish list, he said.

Despite calls for shifting priorities, the bulk of government transportation spending in the United States goes toward roads.

According to the Bureau of Transportation Statistics, in 2018, the federal government spent about $98 billion on transportation, with state and local governments spending another $273 billion. About two-thirds was used for highways, one-fifth for transit and rail, and 13% for aviation.

The need for more funding is great, according to the American Society of Civil Engineers, which routinely surveys the nation's infrastructure needs. Its most recent report card, issued in March, pegged the level of spending needed to bring the nation's transportation networks into a state of good repair by 2029 at $3.1 trillion.

Local leaders also have a vast appetite for money.

A team at Rice University's Kinder Institute surveyed the nation's 100 largest metropolitan areas last year, developing a list of 1,800 proposed infrastructure projects that local officials identified as top priorities. More than a third were transportation projects.

They included a $1 billion investment in the Port of New Orleans and $56 billion for high-speed rail in Texas. But others were far more modest, such as $500,000 for bicycle and pedestrian projects in the Tampa area.

The federal government needs a clear vision for the future it's trying to create, said Adie Tomer, who leads the metropolitan infrastructure initiative at the Brookings Institution, a nonpartisan think tank. For Tomer, that means abandoning the expanding patterns of development that have shaped the nation since its founding.

Meeting the kinds of environmental and social goals the Biden administration has prioritized means looking inward, he said.

"The United States has enough financial resources to invest in infrastructure at any scale that we need to remake the country," Tomer said.

The House last year passed a five-year road, rail and transit funding bill that was designed to get states - which are responsible for spending highway funds - to fix existing roads before building new ones, and to get officials to factor climate change in their planning.

Rep. Peter DeFazio, D-Ore., chairman of the House Transportation Committee and the bill's architect, said any new transportation funding legislation can't simply be an extension of policies crafted in the 1950s.

"The Eisenhower program was 'let's link the country with what he saw - the autobahn in Germany,' " he said. "That was a plan for its time and we were the envy of the world for a while."

DeFazio said it's time to move on: "I'm not going to Eisenhower 8.0. That's not how we deal with our problems of the 21st century in addition to dealing with climate change."

Debate over the 2020 bill was bitter, with Republicans accusing DeFazio of upending the committee's bipartisan approach.

Biden returned to the swing state of his birth for his own infrastructure launch. Pittsburgh's riverside steel plants, fueled by coal, helped build the nation but left the City of Bridges thick with pollution as it hemorrhaged jobs and people. Civic leaders have since sought to tap innovations in transportation and energy to make it a model for cleaner growth and new technology jobs.

Biden said his proposed infusion of federal dollars, paid for by partially undoing Trump-era corporate tax cuts and raising other taxes, would be the biggest American jobs investment since World War II. The plan would dig out and replace all lead drinking water pipes, strengthen American manufacturing and spend hundreds of billions of dollars caring for seniors and people with disabilities, part of what his plan calls "care infrastructure."

About $600 billion would go toward transportation, according to the White House.

Sen. Shelley Moore Capito of West Virginia, the top Republican on the Environment and Public Works Committee, said in an interview before Biden announced his plan that the GOP is open to problem-solving on emissions and building on efforts by automakers to embrace electric vehicles. "There's definitely a willingness to engage," she said.

But in a statement after Biden's announcement, she was sharply critical, calling Biden's plan "a partisan proposal that goes far beyond" the traditional notions of infrastructure and undermines West Virginia's fossil fuel economy.

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The nation is saddled with outdated and, at times, vulnerable infrastructure.

Samaras, an associate professor at Carnegie Mellon, and other researchers calculated that 97% of the interstate highway system was built before 2004 - the year the National Oceanic and Atmospheric Administration started to update rainfall information used to design infrastructure.

"All of those roads were designed for the weather of the 1950s and '60s," Samaras said. If taxpayers are funding new road work, "we need to ensure that the vehicles on that roadway are zero-emissions, and that the infrastructure is built to last so we're not on the hook to rebuild it before we planned."

Tomer said different approaches to overhauling transportation will work best in different parts of the country.

Cities that developed in the 19th century can more easily emphasize bikes and pedestrians. But in large Western cities, the challenge is greater and probably involves promoting denser development, he said.

"No reasonable amount of transit construction can overtake what the built environment tells people to do," Tomer said. "In Dallas - and most of the country looks like Dallas - we have to drive."

In Los Angeles, leaders are bumping up against the limits of car-based development.

LA Metro, the region's transit operator and transportation planning agency, in the fall adopted a $400 billion, 30-year plan to overhaul how the 10 million residents of Los Angeles County get around. The plan aims to more than double the number of daily transit trips to 2.5 million by expanding the rail system and dedicated bus routes. It also calls for 100 miles of new transit lines, nearly doubling the size of the system.

The proposal is explicit about its aim to reduce the number of car trips, but at the same time it would invest billions in highways to try to relieve congestion.

"We are not the enemy of automobiles," said Phillip Washington, chief executive of LA Metro. "What we're saying is you can use both."

Washington served as the leader of the Biden administration's Transportation Department transition team. He said he has briefed Buttigieg on the Los Angeles plan.

The plan is funded, in large part, by local sales taxes, which voters agreed to raise in 2016. Washington said that means his "basket is at least half full" but added that help from the federal government is vital.

The proposal in the nation's second-largest city pays particular attention to what it calls "equity focus communities," those with a large number of lower-income or non-White residents, or where car ownership is low. That work is also a priority of the Biden plan.

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Buttigieg said he thinks of the opportunity to remake infrastructure not only in terms of Eisenhower but also President Abraham Lincoln, who established the nationwide train network. When it came time to engineer a highway system, the process did not abolish trains but recognized a more important role for cars, Buttigieg said.

"We're recognizing a new reality, which is that policy shouldn't revolve around the vehicle, it should revolve around the human being," he said. "Sometimes that human being is in a car, sometimes on a train, sometimes on foot or two wheels, sometimes flying - and all of that needs to be incorporated into our vision."

Walking and cycling have not been a focus of federal transportation policy. Road funding has been routed primarily through state transportation departments, which emphasize large projects for drivers.

Karina Ricks, director of Pittsburgh's Department of Mobility and Infrastructure, said the agency identified gaps in the city's sidewalk network that it wants to fill in to benefit transit users and pedestrians.

But using federal money to build a sidewalk in the city means undertaking a lengthy and expensive review process the state designed with major road projects in mind. Unlocking $1 million could cost $300,000 in planning and turn a four-month project into an 18-month project, she said.

"There is not a different process for those six feet of sidewalk than there is for a six-lane freeway," Ricks said. "It is not logical."

Buttigieg said road-building should be shaped by lessons learned over decades.

"There was a period when we didn't know any better, when we thought that if you had a congested road, you just made it bigger," he said. "And it turns out that sometimes that works, sometimes that just gets more people to drive and the road gets that much more congested."

Rail is among the alternatives being pushed by Biden, a longtime Amtrak rider. His administration has thrown support behind the Gateway Program, which would stretch a new train tunnel under the Hudson River, connecting New Jersey and Penn Station. As a young engineer, Samaras helped on the initial route planning and environmental work for an earlier version of the project, and had sent a set of plans by FedEx to the World Trade Center on Sept. 10, 2001.

They didn't make it, and were returned after the towers fell. The effort languished for years, over politics and resources.

"That's just a couple of tunnels. And it's now 20 years later. Imagine what it's going to look like when we need to build massive amounts of clean and resilient infrastructure for climate change," Samaras said.

He sees this moment as an urgent challenge.

"It's like, are we're going to do this or not?" Samaras asked. "Are we going to basically live off of the successes of the space race and the Cold War through the 2050s? Why don't we build our own successes right now?"