Heath Hall, who became the Federal Railroad Administration's acting chief in June, resigned Saturday after a Politico report raised questions about whether he was simultaneously working another job.
NPR has confirmed the resignation with the Department of Transportation.
"DOT was unaware of the information that is being reported regarding outside work Heath Hall took on during his time at FRA, but those allegations, if true, are troubling," DOT said in a statement Saturday.
Hall had been on leave since early January for what the Department is calling a "family matter."
"Attempts to reach Hall were unsuccessful," Politico also reported Saturday.
According to Politico, after he became acting chief of an agency with a $1.7 billion dollar budget, he may have also been working as a public relations consultant in Mississippi:
"He subsequently appeared at least twice in local media reports last summer as a sheriff's spokesman in Madison County, Miss., where he has long run a public relations and political consulting firm."
"The firm also continued to receive payments from the county for its services from July through December, despite Hall's pledge in a federal ethics form that the business would be "dormant" while he worked at DOT. And Tiffany Lindemann, a former FRA public affairs official who left the agency in September, told POLITICO this week that she had fielded at least three requests from a Mississippi television journalist seeking to speak with Hall during the summer.
This was during a period when Hall was in charge of an agency with a $1.7 billion budget, overseeing the safety of 760 railroads, a multibillion-dollar freight rail industry and the safety of millions of passengers."
As Politico notes, it's not an ideal time for another leadership shake-up at the agency; last year marked the deadliest year in terms of railroad deaths nationwide in at least a decade.
In just the past two weeks, a train carrying House and Senate Republicans to their annual retreat struck a garbage truck, killing one person, and a train collision in South Carolina killed two and injured more than 100 more. In December, an Amtrak passenger train derailed and plummeted off an overpass in Washington state, killing three people.
The FRA hasn't had a permanent leader in more than a year, as Senate Democrats have blocked the confirmation of former railroad executive Ron Batory, who is President Trump's nominee for the position.
Juan Reyes, a New York attorney and the FRA's chief counsel, took over the acting administrator role when Hall went on leave, and he continues to lead the agency now.
NPR's Amy Held contributed to this report.