The Office of Traffic Safety and the California Highway Patrol say a new study shows more than 9 percent of drivers were observed using a cell phone while driving compared to about 6.5 percent in 2014.
The study showed the highest use was among 16 to 24-year-old drivers.
CHP Officer Martin Oliveros says even using a cell phone hands-free can be distracting.
"We're just so much dependent on technology and we don't know when to put it down, as in, when we get behind the wheel, we got to realize that, it can be very dangerous," says Oliveros.
The data show 73 percent of people using cell phones while driving were alone. More people use cell phones while driving in suburban areas, fewer in rural areas.
The National Highway Traffic Safety Administration says 80 percent of vehicle crashes involve some sort of driver inattention.
Just last weekend, a man and his son biking in a bicycle lane in Sacramento County were struck by a car.
Sacramento County Sheriff's deputies said the driver was looking down at a text on his cell phone.
The man was killed, his son is in critical condition.
Chris Cochran with the Office of Traffic Safety says some drivers are too addicted to put down their cell phones when they drive.
"Many more smartphones than ever,” says Cochran. “Almost everybody has a smartphone. Those smartphones have many more ways that you can use them, more apps, more ways that you can communicate and tap things out on them."
The Office of Traffic Safety and UC Berkeley researchers recorded 5,400 observations in 17 counties selected for the study.