A recent study did not find evidence that a California ban on hand-held cell phones while driving decreased the amount of accidents. 

The findings, published in the journal Transportation Research Part A: Policy and Practice, are inconsistent with past research suggesting driving while talking on the phone is dangerous, the University of Colorado at Boulder reported. 

"If it's really that dangerous, and if even just a fraction of people stop using their phones, we would expect to find some decrease in accidents," said Daniel Kaffine, an associate professor of economics at CU-Boulder and an author of the study. "But we didn't find any statistical evidence of a reduction."

The California ban was enacted on July 1 2008. To make their findings the researchers compared the number of accidents that occurred in the six months leading up to the ban with crash data from the six months after. They corrected their data to take into account precipitation, gas prices (which affect number of cars on the road), and other accident-causing factors. 

The study did not determine why accidents failed to decrease, but it may have been because people simply switched to hands-free devices which can be equally distracting. There is also the possibility that many people were not complying with the new law. 

Another explanation is the type of people who are more likely to talk on the phone while driving may also be more susceptible to distracted driving in general; they could be causing accidents by using devices such as CD players and GPS systems. 

"Disentangling these effects will be useful for policymakers in other states who are considering policies to address distracted driving," Kaffine said. "However, our results suggest that simply banning hand-held cellphone use may not produce the desired increase in traffic safety."