The most interesting developments in technology are never the gadgets themselves. It's how they impact society.

Even decades into the cell-phone revolution, for example, we're still trying to figure out how to fit them into our lives. What are the rules for making phone calls in public places? For e-mail during meals? And above all, for using them in cars?

Recently I wrote about Motorola's new Moto-X cell phone. Like most smartphones today, you can control it by voice: have it read new text messages aloud (and dictate replies), check your e-mail, dial a number for you. But this phone goes a step further: to indicate that you're about to issue a spoken command, you don't even have to press a button. You just say, “Okay, Google Now.” The phone is always listening. You never have to touch it or even look at it.

Clearly, that's a step toward greater safety, I concluded. You can leave the phone in your car's cup holder—never take your hands off the wheel, never take your eyes off the road.

Many readers, however, were aghast. “You're promoting the fallacy that when driving, speaking to a cell phone is safer than having to use a hand to manipulate it,” wrote a typical one. “Studies tell us that hands or no hands, eyes on the screen or on the road, using a cell phone while driving causes more accidents than does the abuse of alcohol or drugs. What were you thinking?!”

I was thinking that it must be safer to send texts hands-free. After all, you have to look at the screen to type. If you're looking down at your phone, you're driving a two-ton projectile, blind, at 65 miles an hour.

Besides, the studies referred to by my readers examined talking on the phone—hands-on or hands-free. As we now know, those two methods are equally dangerous. It's not holding the phone that causes accidents—it's mental distraction. (In that regard, the 11 states with hands-free laws are wasting their time.)

But these studies do not address the subject at hand here: the safety of voice texting versus manual texting.

Clearly, people will still text behind the wheel, no matter how much we preach against it, no matter how many states ban it (41 so far). It's like the programs that distribute condoms to teenagers or clean needles to drug addicts: yes, we'd like it better if teenagers didn't have sex or addicts didn't shoot up. But some will anyway. So isn't it better to make their unfortunate activities as safe as possible?

And then something happened that changed my mind. For the first time, researchers finally compared hands-free texting with hands-on texting.

The Texas A&M Transportation Institute studied people driving a closed course under three conditions: while texting by hand, while texting by voice (using Siri for iPhone and Vlingo for Android), and without texting at all.

The results surprised me—and troubled me. Turns out it makes absolutely no difference whether you text hands-free or by voice. “Response times were significantly delayed no matter which texting method was used,” the study says. In each case, drivers who were texting took about twice as long to react as they did otherwise. Incredibly, they also spent less time watching the road, even when they were texting by voice.

It doesn't make intuitive sense. It seems as though texting by voice should be safer than looking at your phone. And to be sure, this was only a single study, involving only 43 subjects.

But if this study's results reflect reality, I'll say it right here in print: I was wrong.

We already knew that hands-free phone conversations are just as dangerous as hands-on, and now we know the same thing about texting by voice. You shouldn't text at all while driving. Your teenagers shouldn't. I shouldn't.

And I've endorsed voice-activated texting for the last time.

SCIENTIFIC AMERICAN ONLINE

More on the science of driver distraction: ScientificAmerican.com/nov2013/pogue