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Driving while texting, amusingly dubbed DWT, has a more profound effect on reaction times than drivers realize, a new road test shows.

A road test run by Car & Driver magazine showed dramatically slower reaction times by two test drivers who tried to brake while reading and, separately, writing text messages. Previous studies on DWT have typically been run in car simulators. The magazine believes its study may be the first conducted in a real vehicle on a stretch of road.

To cover different age ranges, two separate tests were set up on a road course--one with 22-year-old Jordan Brown, a Car & Driver intern, the other with the magazine's 37-year-old editor-in-chief, Eddie Alterman.

Using a Honda Pilot as the test vehicle, both drivers first drove a straight line and were told to hit the brake in response to a light that flashed on the dashboard. That measured their baseline reaction time. The second test had the drivers read a text message while driving; the third asked them to type a message while behind the wheel.

An additional test also compared the effects of DWT with driving while intoxicated, on the same day under the same road conditions. After downing enough alcohol to become legally drunk, the test subjects took to the road again.

The results showed that at 35 mph, it took a sober Brown an extra 21 feet to hit the brake while reading a text message, and an extra 16 feet while typing a message.

At 70 mph, it took him 30 extra feet to jam on the brake while reading a text, and an extra 31 feet while composing.

Those figures compared with an extra 7 feet at 35 mph and an extra 15 feet at 70 mph while intoxicated. However, in his drunken condition, Brown had to be told twice which lane to drive in--a dangerous scenario if he had been in actual traffic.

At 35 mph, a sober Alterman took an extra 188 feet to step on the brake while reading a text, and an extra 90 feet while typing a message.

At 70 mph, he took an extra 129 feet to hit the brake while reading a message, and an additional 319 feet while writing one.

While intoxicated, it took him at extra 7 feet at 35 mph and an extra 15 feet at 70 mph.

The impact of texting on driving.

(Credit: Car & Driver)

"In our test, neither of us had any idea texting would slow down our reaction time so much," said Alterman. "Like most folks, we believe we are good drivers, but the real key to driving safely is keeping your eyes and your mind on the road. Text messaging distracts any driver from those primary tasks."

Car & Driver also noted the relatively safe conditions of its test, compared with driving in the real world. The two subjects drove down a straight line without other cars, signals, or pedestrians.

The full story can be read in Car & Driver's June issue.

Previous studies have also confirmed the dangers of DWT. A recent survey by Vlingo found more than a quarter of respondents admitted to texting while driving.