The San Ysidro port of entry is the main border crossing for non-commercial traffic. Crossing times are notoriously slow at San Ysidro, particularly for those entering the U.S. in cars. Given delays frequently experienced upon entry to Mexico, many cross-border travelers choose to cross on foot. Infrastructure on both sides of the border delivers travelers and commuters to border crossings via respective public transportation systems of which includes the San Diego Trolley blue line that runs from downtown San Diego to the border crossing.