That's a really interesting and practical question about urban waste management. The idea of making trash bin openings smaller to limit what gets thrown in is something many cities have considered, especially to combat litter and improper disposal. The primary goal is to prevent people from tossing in oversized bags, bulky items, or non-compliant waste that can overflow the bin or contaminate recycling streams.
In practice, yes, openings can be designed smaller. You often see this with specialized bins for bottles/cans or paper. A smaller aperture acts as a physical prompt, guiding users to dispose of only certain items. For general waste, however, it's a balance. While it might deter some large litter, it could also lead to more trash being left beside or on top of the bin if people find the opening too inconvenient. This can ironically worsen street cleanliness.
The effectiveness depends heavily on the local context—public education, the types of waste commonly generated in the area, and the frequency of bin emptying. A holistic approach combining thoughtful bin design, clear signage, and public awareness campaigns often works better than relying on opening size alone. It's about designing for desired behavior while maintaining user-friendliness.