In recent years the city government, under Mayor Manny Diaz, has taken an ambitious stance in support of bicycling in Miami for both recreation and commuting. Every month, the city hosts "Bike Miami", where major streets in Downtown and Brickell are closed to automobiles, but left open for pedestrians and bicyclists. The event began in November 2008, and has doubled in popularity from 1,500 participants to about 3,000 in the October 2009 Bike Miami. This is the longest-running such event in the US. In October 2009, the city also approved an extensive 20-year plan for bike routes and paths around the city. The city has begun construction of bike routes as of late 2009, and ordinances requiring bike parking in all future construction in the city became mandatory as of October 2009.

Answer this question, if possible (if impossible, reply "unanswerable"): What cannot travel on Downtown Miami streets during "Bike Miami"?
automobiles