President Trump is “very concerned” about his infrastructure proposal, which was sent to Capitol Hill nearly four months ago, and it remains one of the areas he is “very passionate” about, Transportation Secretary Elaine Chao said Thursday.

The proposal, meant to fulfill one of Trump’s campaign promises, has languished in Congress, where Republicans have balked at funding the 10-year, $200 billion plan. Last year’s GOP-led tax cuts left little fiscal room for the broad rebuilding plan the president has touted repeatedly.

Transportation Secretary Elaine Chao speaks during a Senate Committee on Commerce, Science, & Transportation hearing on infrastructure on Capitol Hill in Washington, Wednesday, March 14, 2018. (AP Photo/Andrew Harnik)

“We want to work with Congress on a bipartisan basis,” Chao said at a Washington Post conference that was largely focused on aviation.

Democrats on the Hill have called for rolling back some tax cuts and spending the money on infrastructure instead, an idea dismissed by GOP members. On Friday, Chao will announce the recipients of more than $2 billion in infrastructure grants, including airports.

Chao also redoubled calls to shift the nation’s air traffic control system out of government hands. Bipartisan objections led one of the proposal’s main congressional backers, Rep. Bill Shuster (R-Pa.), chairman of the House Transportation and Infrastructure Committee, to drop an effort to pass the measure earlier this year.

“The administration’s proposal to take the air traffic control system from [the Federal Aviation Administration] and liberate it from the government shackles of the procurement process which so delays the acquisition of modern, up-to-date” equipment would address frustrations about flight congestion and delays, Chao said.

“Delays mean lost productivity, and also a deterioration in our quality of life. So, again, this idea is going to come back,” she said. “Clearly, we have been unable to get enough votes in the House and the Senate. Until we do, this proposal will not gain greater currency. And so we need to work on that.”

Without citing companies by name, Chao also addressed the tensions raised by recent incidents involving semi-automated and driverless cars, including the self-driving Uber that struck and killed a woman in Tempe, Ariz. in March.

“As we have also seen recently in a number of these accidents, the technology is not fail-safe,” Chao said. “So how do we regulate — as regulators — in a way that will be tech-neutral, that will promote safety without hampering innovation?”

Following her remarks, the National Transportation Safety Board released a preliminary report finding that a Tesla operating in semi-automated “autopilot” mode failed to brake or try an “evasive steering movement” before crashing in California in March. The driver’s hands weren’t detected on the wheel, the agency said. The vehicle also accelerated dramatically seconds before the crash. The driver was killed.

As part of The Washington Post Live session “Taking Flight: Regulating Our Skies,” Sen. Roy Blunt (R-Mo.) pointed to pilot training as a key issue holding up a major aviation bill. Officials and airline executives have raised concerns about what they say is a coming pilot shortage, and there is disagreement about the number of flight hours that should be required for pilots.

“One of the things that’s held the FAA bill back a little bit is trying to reach a conclusion there about how much training and what kind of training is the right training to put a pilot in the air,” said Blunt, who heads a Senate subcommittee on aviation operations, safety and security.

He noted that “the pilots that were trained by the government in World War II, in Korea, in Vietnam are retiring.” He said airlines are “taking more responsibility” in making sure their potential pilots have access to the financing they need to cover training expenses.

Blunt, who also is a member of the Senate Intelligence Committee, said cybersecurity is “probably the thing of greatest concern across the board. Whether it’s the financial structure, the aviation structure, the water infrastructure, so much is dependent now on having a cyber system that works well.”

“It is the quickest way to bring our country to a standstill,” he said, adding that the country needs to sharpen its case to state actors and other adversaries about the consequences of an attack. While the United States “is pretty good at defense, we have no real theory on offense. How do you fight back?”

Blunt said Chao brings “great skills” to the Transportation Department.

“We do need to do a better job of filling the jobs that need to be filled by the president,” Blunt said. Trump has yet to nominate someone to lead the FAA on a permanent basis.

Separately, Chao defended Trump’s nomination of her brother-in-law, Gordon Hartogensis, to head the Pension Benefit Guaranty Corp., saying, “He’s not beholden to the industry.”

Sen. Maria Cantwell (D-Washington), one of Blunt’s aviation subcommittee colleagues, raised concerns about Trump’s recent trade measures.

“Fifty percent of our planes are sold overseas and to overseas markets. You start putting tariffs on steel and aluminum, you start to have an impact,” Cantwell said, referring to Trump’s recent moves imposing such tariffs. Aviation “employs over 100,000 people in the Northwest. . . . We don’t want to see a trade war erupt and make the United States less competitive.”