CA Gov't Code Section 37356

When the legislative body determines that the public interest or convenience requires the construction and maintenance of passageways or other structures under or over any public alley in the city, to connect buildings located on abutting property and facilitate the public use of the streets, it may grant revocable permits for their construction and maintenance. They shall be constructed and maintained so as not to interfere with public traffic on the alley. The city may regulate the use of such passageways or structures.