Safety activists in Massachusetts and around the country are rallying to pass laws that would require drivers to use headsets or speaker phones when they make telephone calls from their cars.
But an expanding body of research suggests that the laws will not prevent crashes as long as drivers are allowed to chat on their phones while driving, with or without a headset.
"Conversations are the problem, not the phone," said Bryan Reimer, a research engineer at MIT's Age Lab who studies driver distractions.
Dialing from the car and searching for those little earpieces when the phone rings take drivers' eyes off the road. And the act of talking on a cellphone, even hands-free, can put drivers in a mental fog that is more distracting than a conversation with passengers in the car, some research has shown.
The Massachusetts bill, passed by the House on Jan. 23, would impose fines for adult drivers who make cellphone calls without a hands-free device. It would ban drivers under 18 from making cellphone calls in the car and would prohibit drivers from sending text messages and e-mails while driving.
The bill has not yet been considered in the Senate, where it faces some opposition from legislators who say police already have discretion to ticket distracted drivers and that a law singling out cellphones would put more surcharges on drivers' insurance bills.
At least two Massachusetts teenagers died in recent crashes blamed on sending or receiving text messages.
Few researchers or politicians dispute the value of banning young drivers from making all forms of calls and prohibiting text messaging behind the wheel. It is the third piece, banning handheld cellphone calls for adults, that has proven most divisive.
Five states plus the District of Columbia have passed hands-free requirements. Those who favor the requirement call it a partial measure, acknowledging that a total ban would be politically impossible.
Most drivers use phones now, and at any given time at least 1 in 20 is engaged in a phone conversation, according to a federal estimate gathered by observers stationed at random street corners. The number is probably conservative because many hands-free calls go undetected.
"Nobody will get rid of cellphones altogether," said Richard Roy, a Connecticut legislator who sponsored that state’s law. "But I think that by passing a law, by having regular news stories about it...it makes people think more about what they’re doing behind the wheel."
Opponents of regulation do not like singling out cellphones, but research indicates that they are the biggest driver distraction.
The most comprehensive study of driver distraction, which tracked 100 cars for more than a year under real road conditions, found that the act of dialing a cellphone increased the risk of a crash by 300 percent.
"There's very little difference between hand-held and handsfree," said Charlie Klauer, a Virginia Tech researcher who worked on the study with the National Highway Traffic Safety Administration.
Klauer believes that dialing and answering calls is the biggest hazard, and that only built-in systems like the OnStar system in some General Motors cars - voice-activated with no buttons to push - can reduce the hazard. Another national study, conducted on a test track, showed that handsfree systems can sometimes distract drivers longer than handheld phones because motorists needed more attempts to dial the right phone number.
Then there is the act of talking, which, according to a study conducted by the University of Utah in 2007, can "induce a form of inattention blindness in which drivers fail to see objects in their driving environment." Even when drivers in the study appeared to be looking at the road, their attention was directed elsewhere, the researchers concluded.
And it is that talking, which few can resist engaging in, that is more problematic than listening.
"It seems there's something really special about our desire to generate speech," said David Strayer, a psychology professor who led the 2007 cellphone study. Strayer has found that speech is more mentally distracting than the relatively passive act of listening, which, he said, seems to require less cognitive energy.
Whether the type or the length of a conversation can affect the level of distraction is a matter of debate. Some researchers insist that any conversation increases the risk of a crash, while others say a short, nonstressful discussion can be relatively safe.
"Million-dollar business decisions are going to be more likely to impact somebody's driving," said Reimer. "Hi honey, I’m on my way home" is less likely to cause a danger.
How is talking on a cellphone any worse than conversing with a passenger? People who sit in the car with the driver are aware of the road environment and will instinctively adapt their discussion to the driving conditions. But a disconnected voice on the other end of the telephone will keep right on gabbing and asking questions, even if the driver gets cut off or has to figure out how to merge into a rotary.
Designers and engineers working on the next wave of driving gadgets are trying to take all of that into account in addressing the symptoms of distracted driving.
A computer installed in the vehicle would detect when drivers take their eyes off the road and then alert them with a beep or a light, hopefully before they hit something.
"Technology now makes it possible to monitor the driver’s condition or state and have some remedial steps so that you can have a more refined response," said Mary Stearns, acting chief of advanced vehicle safety technology at the Volpe Center, a US Department of Transportation research facility in Cambridge, which is involved in developing the technology.
Noah Bierman can be reached at nbierman@globe.com.
