Sidewalk or Bike Trail?

Anybody who's ever listened to me rant long enough knows that I'm a huge proponent of side walks, but what I noticed this morning has me slightly confused.

For starters, my passion concerning sidewalks goes wwwaaayyy back.  I remember jumping double dutch on the sidewalk as a child, riding my big wheel and then my bike on the sidewalk.  It kept us from playing in the street.  In addition, we walked most places within a mile radius.  That minimized the amount of road construction needed because fewer vehicles were on the road unnecessarily.

In addition, with Alabama having some of the highest obesity rates in the nation, we need as many sidewalks as we can get.  I believe more people would walk to close destinations of walking was made safer.

Well, this morning, on my way into work, I actually paid attention to the sidewalk that now runs down McFarland Blvd and under the viaduct of I-20/59.

I've seen a number of pedestrians walking there but never really paid attention to the sidewalk itself.  Now, I'm slightly confused. I've never seen lines running down a sidewalk.  Is this a sidewalk or a bike trail?