My interpretation
We have a man trudging forward on an endless concrete wheel suggesting he's stuck in a rut within his personal life yet the wheel moves in a forward motion with the real world passing by him on the outside. The outside world is just as desolate and grey as his inside stuck-in-rut world which I believe represents how he sees his life as well as the world around him. Very bleak. Very lifeless. Surrounded not by life but by death or the inability to grow and thrive as represented by the lifeless trees.
He feels like his only choice is to move forward because what else is there in this world? The only light inside the moving wheel which he propels is centered around him. Just bright enough to give him hope or purpose against that which tries to bog him down even further (the rain).
The birds flying from beyond and through his personal wheel world represent freedom, hope and purpose but going in a direction which he's not going. If he could only look up and see that he could step outside of the wheel and follow the birds. Not only that but the birds look like seagulls or another type of water oriented bird which suggests that they are flying towards life.
Thanks for this challenge! I look forward to more :)