Transportation Secretary Elaine Chao is resigning from her office, effective Jan. 11.

Chao alerted colleagues Thursday, writing that she was "deeply troubled" by the mob attack at the U.S. Capitol Wednesday, which was incited by President Donald Trump. NBC News reported Wednesday that Chao was considering resignation, and the Washington Post first reported the news Thursday of Chao stepping down.

It has been the honor of a lifetime to serve the U.S. Department of Transportation. pic.twitter.com/rFxPsBoh6t

— Sec. Elaine Chao (@SecElaineChao) January 7, 2021

Chao's resignation will leave the Department of Transportation without a permanent secretary starting Monday. According to agency process, if the secretary leaves office, the deputy secretary is next in the line of succession. That permanent position is currently vacant; DOT General Counsel Steven Bradbury performs the functions and duties of the deputy secretary. 

Chao said in her statement she would help President-elect Joe Biden's DOT secretary pick, Pete Buttigieg, assume the role. Buttigieg still needs Senate confirmation, but the newly won Democratic majority paves an easier path — one that could be traversed this month.

The last time the presidential administration changed from Republican to Democratic, in 2009, Ray LaHood was confirmed as DOT Secretary two days after inauguration.

Under Chao, the DOT prioritized deregulation and collaboration with private entities, evident in the agency's National Freight Strategic Plan, released in September. Subagency officials have lauded her leadership, as those priorities trickled down. 

"As Secretary Chao says, 'We are one DOT,' and multimodal collaboration and cooperation are critical to that effort," James Owens, the deputy administrator of the National Highway Traffic Safety Administration, said during a webinar in August 2020.

Along with releasing the HOS final rule, the FMCSA has floated ideas granting trucking more flexibility, including pausing the 14-hour driving window and allowing drivers under the age of 21 to operate trucks across state lines.

"She has been a champion of infrastructure and transportation safety, effectively leading the Department over the last four years," Rep. Sam Graves, a Republican from Missouri and ranking member of the Committee on Transportation and Infrastructure, said of Chao in a statement.