The findings of a new study, co-authored by a University of Colorado professor, suggest that banning cellphone use behind the wheel might not make roadways significantly safer.

The study, published in the August 2014 edition of the journal Transportation Research Part A: Policy and Practice, examined the number of daily car accidents in California in the six months preceding and the six months after the state adopted a ban on the use of handheld cellphones by drivers July 1, 2008.

Flying in the face of prior research that indicated cellphone use behind the wheel impaired drivers nearly as much as drinking did, the study found no evidence the California ban reduced the frequency of traffic accidents.

"I think there is strong interest in improving traffic safety, and it's just one of the areas that's a priority for a lot of policy makers," said Daniel Kaffine, an associate professor of economics at CU and the study's co-author. "The flip side of that is we need to understand what kinds of policies are good at doing that. In our research, there is no evidence (the California law) was an effective policy."

Kaffine, who at the time of the research was on the faculty at the Colorado School of Mines, said he and study partners Nicholas Burger of the RAND Corp. and Bob Yu, also of the School of Mines, went into the project expecting to find something, but after making adjustments to eliminate variables, even modest decreases in the number of accidents were never found.

"A 5, 10 percent reduction in accidents; that's sort of the range we thought we might see," he said. "But the more we looked at it and the more we looked at it, we realized there was no 'there' there. There was no reduction."

Kaffine said the limited observational time frame was chosen to reduce the number of variables that might skew the data. Examples, listed in a CU news release about the study, include the possible introduction of safer cars on the market, additional changes to state traffic laws or an economic recession that would lead to a decrease in driving.

The data set was corrected for rain and other weather events that might increase the number of accidents, as well as holidays during the observation period, as those, too, are often times when accident numbers spike, Kaffine said. The data was also corrected to reflect the impact of fluctuating gas prices on the number of cars on the road.

Kaffine said the study could mean many things — including that people using Bluetooth technology to talk on the phone remained just as distracted as those using handheld cellphones, or that people who drove recklessly while using a cellphone were prone to that behavior and remained distracted without their phone. But Kaffine doesn't want the study interpreted as proof that using a cellphone while driving is safe; it may simply be that prior studies overestimated the danger.

A study by the Pew Research Center last summer showed that, as of May 2013, 91 percent of American adults owned a cellphone, up from 65 percent in November 2004.

The National Highway Traffic Safety Administration recorded at least 34,000 fatal motor vehicle accidents a year on American roadways for 15 consecutive years, peaking at 39,252 in 2005. But between 2009 and 2012, that number never reached 31,000, hitting an 18-year low of 29,867 in 2011.

In Colorado, texting and driving — as well as any cellphone use by a driver under the age of 18 — has been outlawed since 2009. A bill that would have banned handheld mobile phone use while driving was rejected by state lawmakers earlier this year.

Officials from some Boulder County law enforcement agencies said they feel keeping cellphones out of the hands of drivers can only improve roadway safety.

"We would be supportive of legislation that would limit the use of cellular devices while operating a motor vehicle because the ability to safely operate a motor vehicle is impacted whenever a driver divides their attention behind the wheel," said Cmdr. Heidi Prentup, of the Boulder County Sheriff's Office.

Louisville police Chief David Hayes, who has more than 35 years of law enforcement experience, agreed.

"Anything we can do to keep people focused on the road is a good thing," he said. "I know that the fewer things we have drivers doing that don't involve driving, the better."

Boulder Police chief Greg Testa said he feels Colorado's approach — banning texting and driving as well as cellphone use for minors behind the wheel — is a fair one.

He said a cellphone ban could be hard to enforce, and, anecdotally at least, he has not seen any recent increase in the number of accidents in Boulder due to drivers distracted by their phones.

"I think Colorado tried to balance the different perspectives and the needs of different groups," Testa said.

Audio clips of Kaffine discussing the study can be found on CU's website.

Camera Staff Writer Mitchell Byars contributed to this report.

Contact Camera Staff Writer Joe Rubino at 303-473-1328 or rubinoj@dailycamera.com.