Perhaps you have had this unnerving experience. You’re humming along the Maine Turnpike or some other highway, obeying the speed limit or something resembling it, and you suddenly run up on the rear end of a car going 15 or 20 mph slower than other traffic.

Whoa. Tap the brakes.

Maybe an elderly person. Hey, that’s cool. Or, perhaps, a student driver. Completely understandable.

So, you check the mirror, flick on the turn signal and pull into the left-hand lane to pass. As you pull alongside the slower vehicle, you sneak a glance to the right. What the heck! It’s some jerk having a leisurely conversation on his cell phone.

If you thought you were alone in noticing this strange, dangerous, behavior you’re not, according to a study from a psychology professor at the University of Utah.

Study author David Strayer found that motorists yakking on their cell phones drive an average of 2 mph slower than people not on the phone.

Now, the 2 mph that Strayer has discovered is an average. There are probably some cell phone drivers exceeding the speed limit, and there are probably others who are driving 5, 10 or 15 mph under.

Strayer has estimated that cell phone drivers slow the flow of traffic, adding about 20 hours a year to the average commuter’s drive time.

“People kind of get stuck behind that person and it makes everyone pay the price for that distracted driver,” he told the Associated Press.

Overall, he found that cell phone drivers took about 3 percent longer to drive the same traffic-clogged route than people who were not on the phone. So, if only one in every 10 drivers is on the phone (and we think the rate is much higher than that), the delays really add up.

If 10 percent of the drivers are gabbing, Strayer estimates it adds 5 to 10 percent to the typical highway commute.

Strayer did not even study the effect of text-messaging on driving habits. Evidence shows that a small but growing number of drivers are actually tapping out messages on their phones as they drive – an even more frightening practice.

Last week, a 13-year-old Massachusetts boy was killed while riding a bike by a young man who was composing a text message as he drove. The driver was so unaware of his surroundings that he never even saw the boy, later reporting he thought he had clipped a mailbox.

Other studies have found people talking on cell phones have delayed reflexes similar to those of a drunk driver.

A study at the University of North Carolina found cell phone users are twice as likely to rear-end another car as nonusers.

According to Strayer, the brain works like a computer: the more tasks you ask it to handle at one time, the slower it operates.

Every year, it seems, the Maine State Legislature considers another bill to ban cell phone use while driving. And, each year, those bills fail to pass.

At some point, however, the weight of scientific research – and common sense – will prevail.

We hope it doesn’t take a serious accident or death attributed to text message or cell phone use to turn the tide.