If distracted drivers and icy sidewalks weren't enough, researchers at the University of Maryland have tracked a new danger for pedestrians: wearing headphones.
Closed off to the warning sounds around them, the number of walkers killed or badly injured in crashes in the US tripled from 16 in 2004 to 47 in 2011. It's a small sample, but suggests strolling to your favorite artist's rhythm is unsafe.
In a number of the 116 crashes reviewed, motorists blared their car horns as a warning.
The web site Healthjockey.com analyzed the important factors at play: distraction and sensory deprivation. Walkers with headphones create an attention deficit.
It's reasonable to think that runners and bicyclists create the same hazzard when they are tuned in and tuned out.