Leif Dormsjo, the director of the District Department of Transportation, will resign from his post, effective Aug. 11.

In a letter to his staff sent Tuesday afternoon, Dormsjo said that “it has been an honor to serve Mayor Muriel Bowser and the citizens of the District of Columbia.” He will be entering the private sector and taking a job at the engineering form Louis Berger, where he will be working on infrastructure asset management.

Dormsjo will also resign from his spot as an alternate member of the Metro board of directors — the third vacancy to be announced in a week. Dormsjo was selected to serve on the 16-person board in March 2015, shortly after he was appointed by District Mayor Muriel E. Bowser (D) to head the Department of Transportation.

In an interview Tuesday night, Dormsjo said he informed Bowser of his decision last week, and though she tried to talk him out of it, he said, “I’d made up my mind.”

“I just decided that I wanted to begin the next stage of my career,” Dormsjo said. “It’s never a perfect time to transition, but we’ve accomplished a lot at DDOT over the last few years.”

Dormsjo, a former top Maryland Department of Transportation official, was hired by Bowser in part for his much-needed transit expertise after years in which the city’s effort to build and run the D.C. Streetcar was hampered by a shortage of people with such experience.

Under his watch, the city finally launched the long-delayed and much-maligned streetcar project.

Dormsjo was also instrumental in creating the city’s Vision Zero plan, which aims to eliminate traffic fatalities by 2024. As part of the initiative, the city has began to adopt new strategies for enforcement, public education and street engineering, and also is expected to expand the city’s sidewalk and bicycle network.

During his tenure, Dormsjo pushed for higher traffic fines, including a failed attempt to introduce a $1,000 ticket for “super speeders.” Though the plan was widely criticized, Dormsjo defended it, saying the higher penalties were intended to deter dangerous behaviors responsible for many of the city’s traffic fatalities. Upping traffic fines, Dormsjo said, was key to leveling the playing field in a region where the District’s “fine regime is the weakest.”

Under his watch, DDOT has been building a transit division capable of running its own bus system. This month, DDOT said it is moving toward taking over the management of the troubled D.C. Circulator from Metro. DDOT pays for the service, but Metro manages the contract.

Still, Dormsjo will leave a bus system that is at its lowest levels of reliability. The D.C. Circulator has been struggling with frequent breakdowns of buses, resulting in interrupted service and long waits for passengers. Many of the problems stem from years of maintenance neglect, which were spelled out in multiple audits commissioned by Dormsjo.

In his letter, Dormsjo said he was “very proud of the work we have done together as a team,” and credited Bowser with much of his success.

“Throughout my tenure at DDOT, Mayor Bowser has been a constant and engaged supporter of the agency’s mission to improve safety, deliver vital infrastructure and protect the most vulnerable transportation users,” Dormsjo said. “In every instance, her leadership has been essential to our success.”

Jack Evans, a D.C. Council Member for Ward 2 and chairman of the Metro board, called Dormsjo “one of the best DDOT directors I’ve ever worked with” and praised his performance on the Metro board, where he was known for his pointed questioning and his ability to intensely grill safety officials.

In particular, Evans remembered how Dormsjo derided former Metro safety head James Dougherty’s department as a “paper tiger” — following repeated safety lapses, including a derailment — in a heated exchange in summer 2015 that preceded Dougherty’s resignation the same day.

“It seems to me, by your own testimony today, you’ve got no information about what goes on at WMATA operationally,” Dormsjo said at the time. “What’s the point of having a safety department if you’re not deeply embedded in the organization’s operations?”

Evans praised Dormsjo for “seeing it was necessary back then to shake this place up.”

In a statement Tuesday night, Bowser praised on the departing director’s tenure, saying his leadership made the District a “a more livable, walkable, and bike- and transit-friendly city.”

“Whether it was by moving stalled projects like the DC Streetcar forward or working with WMATA to enhance the safety and security of the Metro system, Leif is someone who could look at and plan for the big picture while taking care of the day-to-day issues like potholes and alley repairs,” she said. “He instilled a data-driven, community-oriented culture at DDOT and led with a real sense of urgency around making DC safer and more efficient for residents in all eight wards.”

The mayor’s office did not immediately respond to questions concerning the circumstances of Dormsjo’s resignation or whom his replacement would be.

Mary Hui also contributed to this story.