This month marks the six-year anniversary of California's ban on the use of handheld cell phones by motorists—a regulation that has now spread to 13 states. So, happy birthday, ban. Your present is a fresh scientific debate over the validity of your very existence.
The body of evidence suggests that driving while distracted by talking on a handheld phone is dangerous. An oft-cited study from 1997 found that using a cell phone more than quadruples a driver's chance of having an accident. California commissioned a study by the University of California-Berkeley in 2012 that concluded that deaths blamed on the use of handheld phones by drivers were slashed by nearly half during the two years following the ban (compared with two years before it).
But something isn't adding up.
"It's possible that people who continued to use their cell phones were people who were more inclined to get into accidents anyway."
Researchers from the University of Colorado and RAND Corporation teamed up with a statistics expert from the Colorado School of Mines to crunch numbers from the large and comprehensive databases of daily accidents on freeways throughout 2008 in nine of California's traffic districts. After controlling for covariates, such as rainfall and holidays, the accident rate during the six months that preceded the ban looked awfully similar to the rate during the six months that followed.
"Across various specifications, we find no evidence of a reduction in accidents state-wide due to the ban," the researchers concluded in a paper published recently in Transportation Research Part A.
The authors of the paper say they are "agnostic" about the cause of their surprising finding.
"It's possible that people who continued to use their cell phones were people who were more inclined to get into accidents anyway," says Daniel Kaffine, an associate professor in University of Colorado-Boulder's economics department and one of the three authors of the new paper. "Riskier drivers might have been the ones who said, 'To hell with it; I’m going to use my phone anyway.'"
Kaffine pointed to research published in 2007 that found that drivers who reported using handheld phones while behind the wheel were more likely to crash than other drivers—even when they weren't yammering away on the phone.
"The other side of the coin is just that maybe it’s the case that cell phones aren't as risky as some of these previous studies have suggested," Kaffine says.
The California Office of Traffic Safety welcomed the study about as warmly as someone receiving a speeding ticket. The office's spokesman, Chris Cochran, argued that the single year's worth of data used by the researchers was insufficient.
"The Statewide Integrated Traffic Records System shows figures for 22 primary collision factors alone, not to mention all the contributing factors," Cochran says. "They vary up and down from year to year, but, overall, each has been trending down for the last decade. By saying that since the overall figures did not drop, then laws against one causal factor, out of the dozens possible, must not be working is illogical."