Residents of Bogota, Colombia, went to work yesterday by foot, bicycle, in-line skate, and horse, observing a day-long ban on the use of private cars. The ban, imposed by Mayor Enrique Penalosa to foster environmental awareness, was the first of its kind in a developing nation. A number of European cities have instituted similar car-free days in the last two years. Buses, taxis, and delivery trucks still plied Bogota’s streets, but an estimated 700,000 private cars were left at home in this city of 7 million. A festive air prevailed and most residents welcomed the car-free day, perhaps in part because nearly 1,100 people, mostly pedestrians, are killed in traffic accidents in Bogota every year.