Statewide regulations that take effect Tuesday require drivers to stay at least three feet away from cyclists while passing or face a $35 fine.
If a vehicle is in the buffer zone and a collision occurs that injures the cyclist, the driver could face a $220 fee.
More than 150 cyclists were killed in car collisions in California in 2012, according to the California Highway Patrol's most recent data. In Los Angeles County, nearly 5,000 cyclists were killed or injured in traffic accidents that year.
Starting Tuesday, CHP officers will be watching cars and other vehicles to ensure that they are giving cyclists the required space. Patrol officers are taught to gauge distances and speeds by sight during their training at the CHP academy and will be able to tell whether drivers are behaving safely, CHP Officer Edgar Figueroa said.
"If we see something that's unsafe, we really will do whatever we can to enforce that," Figueroa said, adding that officers will consider each case individually when deciding whether to issue a citation.
Cyclists can legally use a full traffic lane on California roads. They are required to follow the same traffic laws as cars, including stopping at stop signs and red lights.
Drivers who aren't sure whether they are more than three feet away should err on the side of caution and give more space than they think is necessary, said Colin Bogart, the programs director for the Los Angeles County Bicycle Coalition, a cycling advocacy organization.
He said he hopes that the law will encourage drivers to take a deep breath and wait before speeding past a cyclist.
"Every cyclist can cite a really harrowing moment where someone came way too close and really spooked us in the process," Bogart said.
California is the 24th state to enact a three-foot passing law, according to the National Conference of State Legislatures. Pennsylvania gives cyclists the biggest buffer, requiring at least four feet between cars and bikes at all times.