I just found this video of a pedal/push powered grader on Facebook. I am posting it here as a Facebook link because I can't find it anywhere else yet. Hope this is the right place to put this and it works.
It seems like the bulldozer could be made more effective with a spring mechanism, whereby one could shift from 'propulsion' to 'parked power storage', tightening a spring of some sort to supply a great deal more power over a short time than human legs can provide.
Might be ideal to rig this power storage mode to be charged from the outside of the machine, so one could use steps and their bodyweight rather than try to charge it with pure pedaling.