The law previously required drivers to give a reasonable distance for safety but did not specify what that distance was. The buffer allows bicyclists to safely swerve out of the way of obstructions such as an open car door or a pothole, Prinz said.
If 3 feet is not available, drivers must slow down and wait until they can pass safely. If five cars or more are waiting to pass a bicyclist, the cyclist is required to pull over and allow traffic to pass.
If 3 feet doesn't look like it will be available, such as along narrow rural roads, a driver can slow to a reasonable speed to pass the bicyclist more closely.
Prinz said that most drivers were already giving bicyclists 3 feet or more, but this could help a small portion of drivers better share the road with cyclists.
Bike East Bay is mainly treating this as an opportunity for education and is promoting the law on social media, reaching out to Alameda-Contra Costa Transit drivers and other professional drivers and directing people to the resources on its website, Prinz said.
The law could prove difficult to enforce and will be up to individual police departments on whether to prioritize it.
Prinz said he thinks the law will be more important in collision cases and will allow police to cite drivers who pass too closely and injure bicyclists.
The California Highway Patrol is also strongly promoting the new law.
"The CHP's primary message is to 'Share the Road!' Motorists and cyclists alike have responsibilities to ensure everyone's safety," the CHP's Golden Gate Division said in a statement.
The CHP advises bicyclists to ride with the flow of traffic, obey all traffic laws, be as predictable and visible as possible, and allow other traffic to pass.
Drivers should watch out for bicyclists, give at least 3 feet when passing and should be patient when behind a bicyclist. Cyclists are permitted to ride in the center of a street on narrow roadways.
Prinz said bicyclists and drivers can generally share the road well as long as they practice common courtesy.
"You don't want to antagonize people either behind the wheel or on two wheels," he said. "Using common courtesy can go a long way."