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Anyone who has ever used a cellphone from a driver's seat has to admit that the things are distracting. You have to root for the phone in your purse on the passenger seat when it rings. You have to pull your eyes from the road to make even a simple speed dial. If you're holding the thing to your ear, by definition you can't have two hands on the wheel.

And so banning cellphones while driving should, in theory, cut down on distraction, further reducing the things we do when we're distracted — like getting into car wrecks. Right?

A number of studies, though, including a recent one from economists at the RAND Corporation, the University of Colorado Boulder and the Colorado School of Mines, suggest that cellphone bans haven't necessarily led to fewer car crashes. It's a counter-intuitive result that raises some messy questions for policy about human behavior, and exactly what we're doing in our cars.

"It took a long time for us to convince ourselves that this is what was going on, because we were so sure that this policy must have reduced accidents," says Daniel Kaffine, an economist at the University of Colorado Boulder who worked on the latest research, with Nicholas Burger and Bob Yu.

Their study, published in the journal Transportation Research Part A, looked at about half a million incidents recorded by the California Highway Patrol in nine locations around the state during 2008. That July, a new California law went into effect banning hand-held cellphone use (but not texting) while driving. Kaffine and colleagues focused on the six months before and after the law went into effect, a narrow window that helped eliminate other longer-running changes that might influence crash trends, like improvements in car safety.

Their analysis controlled for additional factors like rainfall, or gas prices (which influence how much people drive). But however they sliced the data, their result was the same: They found no evidence that a ban on cellphone use in the most heavily traveled state in the country led to any reduction in traffic collisions.

How's that possible? The most obvious explanation is that Californians simply weren't following the law. But given the hundreds of thousands of accidents in the state, and the millions of miles traveled there every year, we might expect that even incremental compliance with the law would have had some effect. "Reductions of 5-10 percent, or something like that, would not have surprised us," Kaffine says.

Other explanations are more intriguing: Perhaps people were substituting the risky behavior of using a handheld cellphone for a behavior that may be just as risky, like talking on a Bluetooth. Some evidence suggests that it's the conversation — not the technology — that really distracts us. Or maybe drivers whose hands were freed up by the ban took the opportunity to pick up other distractions instead? CDs? Sandwiches? Lipstick?

Or here's another idea: Maybe the kind of drivers who would comply with a cellphone ban aren't the ones who were causing collisions in the first place.

"Flaunting the law is risky," Kaffine says. "So a driver who regularly behaves in risky ways in their car may just simply ignore the ban. We could see compliance going up — but it’s compliance by people who are already low-risk drivers."

Maybe talking on the phone in a car is a symptom of riskiness, not the risky behavior itself. Simulated driving studies dispute this explanation. But those same simulation-based studies suggested that states would see a much larger reduction in collisions than they have so far.

None of this means that driving while using a phone isn't dangerous, nor that bans on such multi-tasking are bad policy. But something may be happening in between the theory behind these laws and the real-world implementation of them. Maybe the fines needs to be higher and the enforcement stronger? Or we need to figure out who's really complying here.

"I wouldn’t necessarily want to conclude that the implication is that we shouldn't have these bans in place," Kaffine says. "The implication is that we should think harder about these things, and collect more data."