Prospect Park is typically filled with runners and bikers. Starting Tuesday, the park is officially car-free. The car ban in Brooklyn's backyard is years in the making. The park's West Drive has been closed to traffic since 2015. Before Jan. 2, 2018, the park's East Drive was open to traffic on weekdays during morning rush hours. But the city said that walkers, runners, and cyclists outnumbered cars more than three to one.