Be very careful when you are on Market Street and Powell Street in San Francisco. These areas are the heart of cable car routes and feel very seedy especially after hours. I have found, however, that if you walk with a purpose (and preferably with a group) people don't bother you. Make absolutely certain that you know exactly where you need to go (such as the Powell Street BART station) BEFORE you leave wherever you are leaving from. USE COMMON SENSE!