PhotoWe hear all the time about how disastrous distracted driving is, how using a cell phone behind the wheel is like driving drunk. Former Secretary of Transportation Ray LaHood made it a major initiative and spent all kinds of time and money on studies and educational campaigns.

But now a study from Carnegie Mellon University and the London School of Economics and Political Science finds that talking on a phone while driving does not increase the risk of a crash. 

For the study, Carnegie Mellon's Saurabh Bhargava and the London School of Economics and Political Science's Vikram S. Pathania examined calling and crash data from 2002 to 2005, a period when most cell phone carriers offered pricing plans with free calls on weekdays after 9 p.m

No correlation

They compared data from mobile network operators and accident reports and found that there was no direct correlation between the number of phone calls made during a certain time period and the number of crashes during the same time.

"Using a cell phone while driving may be distracting, but it does not lead to higher crash risk in the setting we examined," said Bhargava, who is an assistant professor of social and decision sciences at CMU. "While our findings may strike many as counterintuitive, our results are precise enough to statistically call into question the effects typically found in the academic literature. Our study differs from most prior work in that it leverages a naturally occurring experiment in a real-world context."

Saurabh Bhargava

In the study, the researchers identified drivers as those whose cell phone calls were routed through multiple cellular towers. They first showed that drivers increased call volume by more than 7 percent at 9 p.m., when the calls became free. They then compared the relative crash rate before and after 9 p.m. using data on approximately 8 million crashes across nine states and all fatal crashes across the nation.

They found that the increased cell phone use by drivers at 9 p.m. had no corresponding effect on crash rates.

Additionally, the researchers analyzed the effects of legislation banning cell phone use, enacted in several states, and similarly found that the legislation had no effect on the crash rate.

Drivers may compensate

"One thought is that drivers may compensate for the distraction of cell phone use by selectively deciding when to make a call or consciously driving more carefully during a call," Bhargava said. "This is one of a few explanations that could explain why laboratory studies have shown different results.

"The implications for policymakers considering bans depend on what is actually driving this lack of an effect.  For example, if drivers do compensate for distraction, then penalizing cell phone use as a secondary rather than a primary offense could make sense," he said. "In the least, this study and others like it, suggest we should revisit the presumption that talking on a cell phone while driving is as dangerous as widely perceived."

Pathania, a fellow in the London School of Economics Managerial Economics and Strategy group, added a cautionary note: 

"Our study focused solely on talking on one's cell phone. We did not, for example, analyze the effects of texting or Internet browsing, which has become much more popular in recent years. It is certainly possible that these activities pose a real hazard."

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