Have the trash can in sections that raise up and spin a quarter turn to lock in place. There are three sections, each about a foot and a half high. the bottom section is non moving, while the other two rings lift up and twist, locking the second ring, then the outer ring lifts and twists making a full size garbage can. When the trash is emptied, the garbage man could easily just spin the top of the can and it would collapse, leaving a small, more aerodynamic trash can. Maybe if the garbage man spinning it doesn't work out, maybe it could work on the pressure of the garbage pushing out on the walls to lock them in place so when its empty it falls. Also, it would allow for the trashcan to be lower profile while it has small amounts of trash in it. There could be a way to lock down the rings to the base and then the cans to each other (stacked and locked) so you could pull both cans with one handle.