Commuters on a Metro train. (Linda Davidson/The Washington Post)

A longtime push to bring Metro to Prince William County, expanding the system’s 117 miles of rail into the Route 1 corridor or farther west to Manassas, faces immense hurdles. Such a massive regional undertaking would have to be approved by Congress and the three jurisdictions served by Metro.

That doesn’t mean that Corey A. Stewart (R-At Large), chairman of Prince William’s Board of County Supervisors, and other elected officials aren’t going to give it a shot. On Tuesday, the board will consider a resolution to support a bill, introduced by Rep. Gerald E. Connolly (D-Va.), that would allow a federally funded feasibility study on expanding Metro to the county. Connolly is seeking to add the board’s approval to a list of supporters that includes the Prince William Chamber of Commerce, the Dale City Civic Association and the town of Dumfries.

But regardless of a potential study’s findings, Metro says it cannot devote resources to expansion until a backlog of core-capacity needs across the system are addressed, including a combined $6 billion in improvements that are not expected to be started until 2025.

Construction, then, would be at least a decade away, Metro Planning Director Shyam Kannan said, and probably further off — 2030. The already crowded Rosslyn Metro station — maxed out by traffic on the Orange, Silver and Blue lines — can’t handle any additional trains, he said, so a new station would have to be built or capacity increased for trains to begin serving residents deeper into Northern Virginia.

“Until our core-capacity issues are resolved, both fully funded and built, there is no room for system expansion at this point,” Kannan told county supervisors. “That would include any jurisdiction, including Prince William.”

Stewart called the presentation a sobering dose of the “cold, stark reality” of bringing Metro to a county — fast approaching a population of nearly 500,000 — whose residents take 10,600 Metrorail trips daily. He admitted that the county does not have the density or scale of development needed to meet Metro’s criteria for expansion but added that it could by the time any track is put down.

For Metro expansion to be feasible, Kannan said, Prince William would need any two of the following criteria: a density of at least 12 to 18 households per acre and 19 to 26 employed residents per acre; a ridership of at least 3,500 to 7,000 per mile; and an environment that is 50 percent to 65 percent developed, by a Washington Metropolitan Area Transit Authority metric.

A federally funded study is the initial hurdle in an extended process that could span several decades, said Supervisor Frank J. Principi (D-Woodbridge), who introduced the resolution supporting Connolly’s bill. The first feasibility study for the Silver Line, he noted, was conducted in 1985. Passengers didn’t board one of its trains until 29 years later.

Principi invited Kannan to a recent meeting to give board members an idea of what the expansion process, familiar to neighboring Fairfax and Loudoun counties, would look like. He said his constituents often ask him about bringing Metro to Prince William, and he acknowledged the challenges of doing so.

“This is not a cakewalk,” he said last week . “This is not going to be simple. Until we get a feasibility study in place and we get to those findings, we’re just not going to be an informed community about what our options are, what our price tag is associated with it.”

In his presentation to supervisors, Kannan said that the Yellow Line bridge, one of Metro’s two Potomac River crossings — the other is the Rosslyn tunnel — is at capacity. To address capacity issues in the system’s core, which handles 80 percent of morning trips, Metro would need to install additional escalators, stairways and mezzanines in 12 core stations, restore rail service to a point of reliability and increase the prevalence of eight-car trains, which make up about 33 percent of the system.

“At Rosslyn, the station now — which hosts Blue, Orange and Silver — we are pushing as many trains through that station as physics will allow,” Kannan said. “Until we have additional capacity through that constrained station, we are unable to add additional train capacity into Virginia.”

Kannan also laid out the costs of taking on such an expansion. Building rails would cost between $100 million and $600 million per mile (with tunneling as the most expensive option), according to Metro’s presentation, while stations would come at a cost of $80 million to $300 million each. Eight-car trains, which would be the standard by the time any such expansion might be undertaken, will cost between $17 million and $22 million each.

The comparable Silver Line, which opened in July 2014, cost about $255 million per mile of track, Kannan said.

Connolly said a Prince William expansion has widespread support among county residents and elected officials, who see the potential for attracting new business and residential growth. Metro’s problems of today, he said, should not be seen as a barrier.

Just last week, the National Transportation Safety Board said Metrorail’s safety problems are so severe and persistent that federal officials should take a much stronger role in monitoring it. In addition to safety problems, Metro has been under increased scrutiny over a multitude of management and financial failures.

“That’s a here-and-now issue,” Connolly said. “We can’t make decisions that are probably 15 and 20 years out based on today’s problems in Metro. Otherwise, we might as well say, ‘Metro is complete, we will never consider another extension because we’ve got problems today.’ This is about the future.”

Stewart, too, said Metro could be a boon to Prince William. But he is realistic about its implications for the county down the line.

“If we did join the Metro path, it would be in­cred­ibly expensive and pretty much devour our transportation programs in Prince William County,” he said. “We’d have no money left for any roads — that’s for sure.”

Connolly said hopes were similarly low for the Silver Line, the massive expansion project he fought for on Capitol Hill. It had basically stalled in the mid-1990s, and it “consumed” 19 years of his career, he said.

“It was dead. Gone. Nobody was going to do it,” he added.

Principi said that regardless of the hurdles, a growing region should look into expanding its transit system.

“We can walk and chew gum at the same time,” he said. “I think we can do both as a region. I mean, this is the nation’s capital. I think we have the capacity, the resources to do this.”