David Strickland, chief of the National Highway Traffic Safety Administration for the past three years, is stepping down, the agency confirmed.

Strickland’s acting successor will be Deputy Administrator David Friedman.

This is the second top personnel move at the Transportation Department resignation this week. Deputy Transportation Secretary John Porcari’s planned departure was announced Wednesday.

Strickland headed NHTSA during implementation of a national fuel efficiency program and a number of safety initiatives, including efforts to combat distracted driving and test vehicle-to-vehicle communications.

Also during Strickland’s tenure, the agency has worked on rules that would require electronic stability control systems and speed limiters on heavy-duty trucks. Both rules are scheduled to be finished next year.