The tunnel was fully closed Sunday for 24 hours, marking the start of a 14-month project tied to seismic upgrades at the Chinatown Public Health Center, which sits above the tunnel's eastern entrance.
While the closure is temporary, traffic changes associated with the project are expected to impact commuters for months. Beginning Monday morning, the tunnel's westbound bore will reopen and carry traffic in both directions for the next seven months while work continues.
Some business owners say they understand the need for the upgrades.
RELATED: SF's Broadway Tunnel to be shut down Sunday for about 24 hours as crews begin 14-month project
"I think it's OK, because they have to get it done and do what they have to do," said Abby Huang of the Chinatown Merchants United Association and owner of House of Dim Sum.
Huang says the community will need to adjust as construction moves forward.
"I think what we need to do now is be patient when they're doing the construction," she said.
Sunday's closure forced drivers onto a detour around the tunnel. During a test run, ABC7 Eyewitness News' van took about seven extra minutes to travel from Larkin Street and Broadway to Chinatown.
Not all merchants are optimistic about the impact on neighborhood businesses.
"I just think it's going to be bad for business in Chinatown, because it's really hard to get a place to park," said Jimmy Chen, owner of Duck Hing Express. "I think people will just avoid it. If there's going to be a lot of traffic, there's no point."
The traffic changes also coincide with the first day of classes for students in the San Francisco Unified School District. Superintendent Dr. Maria Su urged families to plan ahead and expect delays.
"We're asking families to have a little extra patience and spend a little extra time to get to school," Su said.
Residents who regularly use the tunnel are also concerned about spillover traffic on nearby streets.
"I honestly think it's going to cause a lot more traffic," said Larkin Street resident Baani Sharma.
Sharma worries drivers trying to avoid congestion inside the tunnel will divert onto neighborhood streets.
"I feel like with one lane closure, all the back streets to get to the Financial District will get a lot worse. A seven-minute commute could take 40 minutes now," she said.
SFMTA says digital message signs will be posted to alert drivers to changing traffic conditions and alternate routes. Transportation officials are encouraging commuters to allow extra travel time and consider taking public transit whenever possible as construction continues.