The California High-Speed Rail authority is seeking fresh federal money for its Central Valley project, months after the Trump administration pulled $4bn in previously committed federal funds from the programme.

The withdrawal, executed by the US Department of Transportation under President Donald Trump, reversed funding that had been directed to the planned San Francisco–Los Angeles rail line, and left the state authority carrying the full cost of ongoing construction in the San Joaquin Valley.

Despite the loss of federal support, the authority has continued to advance construction on the approximately 300 km Central Valley segment between Madera and Bakersfield, working from a mix of state cap-and-trade revenue and previously obligated federal grants. The new funding request signals that Sacramento intends to return to Washington for money rather than rely exclusively on state sources.

The $4bn clawback is the largest single federal withdrawal from the programme to date, and it follows years of political conflict over the project between California's Democratic leadership and Republican administrations in Washington. The authority's decision to seek new federal money sets up a fresh test of whether the project can attract federal partners in the current political climate.

California's high-speed rail programme has been under construction since 2015, when work began on the Fresno River viaduct near Madera. The authority has repeatedly revised its cost estimates and schedule, and the current scope calls for an initial operating segment in the Central Valley, with electrified track, trainsets and stations.

The funding dispute is only the latest chapter in a long-running disagreement over federal support for the project. During his first term, Trump threatened to cancel a $929m federal grant before leaving office; the Biden administration subsequently restored and expanded federal support, including the funds now withdrawn.

For the authority, the stakes are operational as well as financial. Every dollar shifted from federal to state sources constrains the timeline for tracklaying, electrification and systems work on the Central Valley segment, which represents the only portion of the network where construction is underway.

California Governor Gavin Newsom's administration has defended the project as essential infrastructure for the state's transportation capacity, while federal critics have labelled it wasteful and poorly managed. The authority's own estimates put total programme costs well above the figure voters approved in 2008, when Proposition 1A authorised $9bn in state bonds for the system.

The request for new federal money comes as the authority continues to report progress on construction packages across the valley, including viaducts, grade separations and station sites in Fresno, Hanford and Bakersfield. Whether Washington re-engages financially will determine the pace at which those packages convert into operable infrastructure.

The authority has not publicly detailed the size of the new federal request or the programmes it intends to target. Its next federal funding conversations will take place against the backdrop of a divided government in which high-speed rail has few committed champions outside California.

The outcome will shape not only the Central Valley segment's completion date but also the prospects for extending the system toward the Bay Area and Los Angeles, extensions that remain unfunded and unscheduled.