Polly Trottenberg, under secretary of transpor­tation for policy at DOT, has been nominated New York City transportation commissioner by new Mayor Bill de Blasio. She earlier served DOT as assistant secretary.

Trottenberg also was the inaugural executive director of Building America’s Future, a bipartisan nonprofit organization supporting increased investment in infrastructure and major transportation policy reform.

The new mayor supports expanding bus rapid transit in the outer boroughs, increasing bicycling, reducing traffic ­fatalities, and boosting the efficiency of city streets.