With the new year a new law went into effect in California that lets drivers send and receive text messages or emails so long as they communicate through a hands-free or voice-operated system. Dictating an outgoing message or listening to an incoming one while behind the wheel is now fair game. When the bill first passed its author, then-Assemblyman Jeff Miller of Orange County, said it allowed Californians to text and drive "safely and responsibly."
The evidence from behavioral science begs to differ. Years of work by psychologists, most notably David Strayer of the University of Utah, has demonstrated that people suffer significant impairment when they use a cell phone while driving. But the public's desire to do both things at once is so great that many are willing to overlook the evidence. A last-ditch plea by the National Safety Council for California to repeal the law — citing the "overwhelming amount of research" questioning the safety of hands-free technology — fell on deaf Bluetooths.
A few years ago, in a groundbreaking study, Strayer and colleagues compared the performance of cell phone users to drunks in a driving simulator [PDF]. Study participants talking on a cell phone — handheld and hands-free alike — had slower brake times and were involved in more simulated accidents than when they weren't chatting. Their cognitive impairment was roughly as great as that of participants who got in the simulator after drinking enough screwdrivers to register a .08 percent blood-alcohol content.
More recent evidence, focusing on texting, has made similar conclusions. In one study published last year, a team of researchers at the Virginia Tech Transportation Institute evaluated the performance of drivers texting on a closed road. Some texted from their handheld device, which previous research had already concluded was dangerous, while others texted through an in-vehicle system connected to Bluetooth.
No surprise that drivers who texted by hand drove very poorly: they reported greater mental demand during the drive, took longer glances away from the roadway, and steered worse compared to baseline driving performance. Those who used the in-vehicle system did a little better. They didn't have much problem receiving text messages through the in-car system, but sending them posed a problem.
Even sending a voice text as simple as "I'm stuck in traffic" led drivers in the study to glance off the road more often and longer than usual, and they too reported a higher mental demand during this part of the test:
A common response to the hands-free communication evidence is that drivers talk to passengers all the time without a problem. Actually, from a psychological standpoint, the two tasks are very different. Strayer's research, in particular, has shown that the impairment of cell phone use on the road is not just physical (as in the act of texting or dialing or activating the hands-free system) — it's also cognitive.
Strayer and colleagues have found that drivers engaged in hands-free communication create weak memories of objects in the driving environment, suggesting a great deal of attention is drawn away from the road [PDF]. In contrast, conversations with passengers in the car often incorporate traffic into the discussion or shift depending on the complexity of the driving situation — "thereby mitigating the potential negative effects" [PDF]. A doctor discussing the topic in the New England Journal of Medicine in 2010 said she makes the point to her own patients like this:
When patients aren't convinced, I ask them, “How would you feel if the surgeon removing your appendix talked on the phone — hands free, of course — while operating?” This hypothetical captures the essence of the problem — the challenge of concentrating fully on the task at hand while engaged in a phone conversation.
The auto industry probably has invested too much in vehicle communication systems to go back, and to be fair, using these systems to talk or text seems measurably safer than the "old" way of doing so by hand. At the same time, the risk is there. Lawmakers aren't doing the public any favors when they pretend it's not.
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