Bay Area officials say a critical upgrade to increase BART’s passenger capacity is being held up needlessly in Washington, where a $1.25 billion federal grant application has languished for 18 months.

The issue picked up momentum this month as California’s U.S. senators sent a letter to the U.S. Department of Transportation secretary urging immediate action on the grant application.

On Wednesday, BART officials upped the pressure, saying that a fatal crash on the Bay Bridge, which jammed traffic into the city for hours and brought 10,000 additional passengers to the train system, illustrated the need for improvements.

“Standing still for us is not an option — it’s not an option for the region’s economy, and it’s not an option for BART,” General Manager Grace Crunican told a throng of reporters at the West Oakland Station, as trains rumbled overhead.

“It’s essential that the federal government step up to the plate,” she added.

BART is seeking the grant to buy a new train-control system, new rail cars, a set of storage tracks for its Hayward yard and traction power substations to carry more people through its Transbay Tube. About 27,000 passengers currently move through the tube every hour on 23 trains of varying lengths. The improvements would boost that number to 39,000 people by allowing BART to run 30 10-car trains each hour.

But officials at the Federal Transit Administration let the grant application sit for a year and a half, preventing it from moving to the next phase. A spokeswoman for the administration did not respond immediately on Wednesday.

“We’re running at the limit of what our current train-control system can handle,” said Duncan Watry, project manager for core capacity at BART. He and other transit officials hope to get the application approved by the end of the year so they can award a new train-control contract. The entire project will cost $3.5 billion, but two-thirds of that money will come from state and local funds, including voter-approved Measure RR.

On Wednesday morning, when a box truck collided with a Golden Gate Transit bus on the Bay Bridge, killing one person and causing gridlock throughout the Bay Area, BART officials saw an opening. At a news conference that afternoon they tried to rally support for the federal funds, saying the bridge wreck shows how essential BART is to the region: While traffic crawled for miles along Interstate 80 and spread into residential neighborhoods, the agency boosted service by adding train cars and operators.

If the Transbay Corridor Core Capacity Program grant is postponed into next year, BART will lose money. The agency estimates its costs will rise $10 million for every month that awarding the train-control-system contract is delayed beyond December. And the cost of new rail cars could also escalate, Watry said.

“We’ve been jumping through more and more and more hoops,” said board President Bevan Dufty.

Earlier this month, several Bay Area congressional leaders, including Sens. Kamala Harris and Dianne Feinstein, sent a letter to U.S. Department of Transportation Secretary Elaine Chao, urging her to review and advance the grant application.

“BART’s project is a shining example of the type of infrastructure investment that the Core Capacity program was designed to support,” the letter said. It noted that federal authorities gave the core capacity project application the “highest possible technical grade,” although they left it stuck in administrative limbo since December 2017.

Some observers in the transportation world speculate that BART is being stymied by politics.

“BART’s coming to the federal government with one of the best single projects that you’re going to see,” said Randy Rentschler, legislative director of the Bay Area Metropolitan Transportation Commission.

Yet the transit agency is hitting the headwind of a presidential administration that generally dismisses public transit, Rentschler said. And it’s hitting the tide of partisan politics: BART is a vital link for one of the bluest, most Democrat-leaning areas in the country.

The transit administration’s budget for next year disburses $1.5 billion among mass-transit projects with grant applications approved by the Obama administration, such as Los Angeles’ extension of the Purple Line and the electrification of Caltrain. Most of them lie in blue states.

But the budget also proposed cutting funding for new projects down to $500 million, enough for “zero new projects, ever,” said the D.C.-based transportation industry newsletter, Eno Transportation Weekly.

By contrast, data from the U.S. Department of Transportation show the administration is shifting funds to highways and bridges. The majority of last year’s discretionary transportation grant awards went to rural areas, and the urban grant awards were largely in red states clustered in the South, the Southeast and the Midwest.

One example is a $9 million grant for the Nenana Bridge Project in Nenana, Alaska. It would improve “economic competitiveness and quality of life by providing year-round access to approximately 650,000 acres of developable energy resources,” according to the grant description. Petroleum companies have long eyed the Nenana basin for oil drilling.

So, while the Trump administration is spending money to build bridges in the wilderness, it’s taken “an aggressive stance toward stopping public transit,” which could explain why BART’s plans got stuck, Rentschler said.

To MTC Commissioner Nick Josefowitz, the BART grant delay harks back to President Trump’s decision this month to cancel $1 billion in funds for high-speed rail in California. But whereas bullet trains are still an abstract, far-in-the-future idea, BART’s project is immediate and vital, Josefowitz said.

“It’s going to move way more people” than high-speed rail, Josefowitz said. “And it’s an essential link for one of the most economically productive regions in the country” — and a large tax base to support the federal government.

As the Bay Area’s economy and population boom, demands are piling up on its already-stressed rail system. A new MTC study predicts that San Francisco would add 300,000 jobs by 2040, creating an impossible haul for BART. At that rate, the Transbay Tube would reach capacity by 2027. Officials are looking at design concepts to start building a second tube within the next decade, but they haven’t identified funding.

With such daunting challenges ahead, transit officials hope to stretch their existing infrastructure as far as it will go. But they can’t grind along forever on equipment and technology that dates to 1972.

Rachel Swan is a San Francisco Chronicle staff writer. Email: rswan@sfchronicle.com Twitter: @rachelswan