The great thing about headphones is they allow you to tune out the rest of the world. And the worst thing about headphones is that they allow you to tune out the rest of the world.

Too many headphone-wearing pedestrians -- most of them kids and young adults -- forget the rest of the world even exists once their music starts playing, and it's leading to some terrible tragedies.

The number of people struck by cars, trains, trucks or buses and killed or seriously injured has tripled in just six years -- and, to the surprise of no one, more than two-thirds of the victims were under 30 years old.

The overall numbers aren't that eye-popping: Just 16 injuries and deaths in 2004-2005, growing to 47 by 2010-2011, or 116 in total over those six years, according to the research published in Injury Prevention.

But that's not the complete picture -- just what researchers were able to come up with by scouring Google News and a couple of federal injury databases.

I'd bet the true numbers are higher -- much higher, and in the coming years distracted walking might turn into as big an issue as distracted driving, especially in pedestrian-crowded cities.

After all, the new study looked at just music players and headphones -- but plenty of other people talk, text and/or e-mail while walking, leading to even more serious injuries.

One recent study found more than 1,000 walkers -- again, mostly younger people -- sent to emergency rooms for trips, tumbles and other accidents that happened while they were talking or texting in 2008.

That was double the number of injuries from the previous year... which was almost double the number of injuries from the year before that -- and we're not talking stubbed toes and bruised bottoms here: Distracted walking has been causing concussions, sprains and fractures.

And, as the newest study shows all too well, death.

You're probably too smart to try to text, listen to music and cross the street at the same time. But your kids and grandkids may not be getting the message.

Be sure to let them know -- even if you have to text them to get their attention.