The challenge is met nicely with this photo... I particularly liked some of the images in this challenge that took alternative paths from the 'normal' modes of transportation that everyone would normally think about.
I think you did a good job of composing the legs/feet on the right hand side of the frame... that definitely works better than centering in a horizontal frame. I think this photo could also potentially be strong with centered legs/feet in a vertical frame, allowing the feet to fall on the bottom horizontal third line...
I think this composition could use a little color also... The skin tone of the legs stand out nicely, but if there was some other element of color here, i think it would benefit the image. Maybe some colored socks or something would create that little surprise element that makes the photo really jump.
I also think the shoe may be a little close to the bottom of the frame for comfort... A little extra breathing room there could strengthen the composition as well...
Nice composition - 3 levels of gray, with a tiny corner of green! And walking right down the line are a very interesting pair of shoes. Wish the shoes were completely sharp.