Department of Transportation Commissioner Polly Trottenberg is leaving Mayor Bill de Blasio's administration next month, City Hall confirmed Monday.

Trottenberg is the longest-serving commissioner in the agency's history and one of the the longest-serving commissioners in the de Blasio administration. 

Since being appointed to lead the department in January of 2014, Trottenberg oversaw a push to increase speed cameras to 750 zones, helped expand bike and bus lanes and implemented Vision Zero, a program designed to decrease traffic deaths on city streets. 

“We all owe Polly Trottenberg a debt of gratitude for her incredible service to New York City,” de Blasio said in a statement. “She is a tireless and talented public servant who has made our city safer, fairer, and more accessible. I’m proud to have worked so closely with her, and I wish her all the best in whatever comes next.”

The commissioner's departure comes at a critical time for the city, which is struggling as a result of the coronavirus pandemic, but also as the de Blasio administration nears its end. 

Trottenberg has not yet announced her next move, but earlier this month she was tapped to work on the Biden-Harris transition team advising the incoming federal administration on transportation issues. 

In the last few months, the agency has focused part of its work in helping to oversee the expansion of sidewalk cafes, allowing restaurants to offer outdoor service in the wake of the pandemic. 

“I will always be grateful to Mayor de Blasio for the incredible opportunity to serve the city I love so much, and especially for the chance to lead the 5,800 dedicated public servants at DOT,” Trottenberg said in a statement. “I have been honored to work with them and see the passion, creativity and dedication they bring every day to serving New Yorkers, especially during the pandemic of the last eight months.  For now, I just say thank you, one and all.”

Trottenberg's departure comes in the heels of other high profile resignations from the mayor's cabinet and it's likely to give way to other departures. In the past three months, the health commissioner and the sanitation commissioner have left the administration.