A major traffic artery in San Francisco was closed Sunday, and will remain partially closed on Monday, just as San Francisco Unified students head back to class for the first day of school. The Broadway tunnel near Russian Hill, Nobb Hill and North Beach is undergoing improvements. It was closed since 7 a.m. Sunday. The city says the closures have to do with updates needed to improve earthquake safety at the Chinatown Public Health Center, which sits right on top of it. The full closure is set to end at 5 a.m. Monday, just in time for the morning commute on the first day of school for San Francisco Unified students. But a partial closure will remain in place for much longer. NBC Bay Area Alyssa Goard has more in the video above. ...read more read less