The city shares a 15-mile (24 km) border with Mexico that includes <answer>two</answer> border crossings. San Diego hosts the busiest international border crossing in the world, in the San Ysidro neighborhood at the San Ysidro Port of Entry. A second, primarily commercial border crossing operates in the Otay Mesa area; it is the largest commercial crossing on the California-Baja California border and handles the third-highest volume of trucks and dollar value of trade among all United States-Mexico land crossings.
How many border crossings does San Diego share with Mexico?
two