The law, which went into effect on July 1, 2008, prohibits the use of talking or sending text messages on a handheld cell phone while driving.
When the law was first enacted, officers gave numerous warnings and made education efforts about the safe and legal way to use a phone while driving, police said. Drivers are allowed to use cell phones as long as they are connected to a hands-free device.
In the last six months of 2008, Petaluma police issued 156 citations for breaking the cell phone law.
After launching an aggressive enforcement campaign in July, police issued 483 citations in the last six months of 2009. Officers issued more than 840 citations for breaking the cell phone law during the entire year of 2009, according to police.
"We have tried with patience and understanding to allow people time to understand the law and purchase hands-free devices," Petaluma police Lt. Tim Lyons said in a statement.
"The only way we are going to change the behavior of the motoring public on this issue now is aggressive and proactive enforcement through the issuance of citations to those who chose to ignore the law and the dangers associated with these violations," Lyons said.