That's a great question that gets into the practical details of urban design! From my experience observing cities, rectangular trash cans often have a slight edge in dense urban environments for a few key reasons.
First, it's about space efficiency. Rectangular bins fit snugly against walls, buildings, or in corners without leaving awkward gaps. This is crucial on crowded sidewalks where every inch counts. A round can, while aesthetically pleasing, always leaves that curved wedge of unused space, which can be a nuisance in tight spots.
Second, consider capacity and collection. The straight sides of a rectangular design typically allow for a larger internal volume compared to a round can of a similar footprint. More importantly, they align with the rectangular compartments of most modern garbage trucks, making mechanized collection faster and more efficient. Workers also find it easier to line up rectangular bags inside them.
Then there's stability and stacking. A rectangular bin with a flat base and sides is inherently less likely to tip over in windy conditions or if bumped. For areas using liner bags, the shape provides a much easier fit. Some modern rectangular models are also designed to be modular, allowing them to be linked together for recycling streams (trash, paper, plastic) in a neat, compact unit.
That said, round bins aren't without merit. They're often perceived as more classic or decorative, work well in open parks or plazas where space isn't a constraint, and have no corners for debris to get trapped in. But for the typical sidewalk, transit stop, or busy street corner, the rectangular design usually offers more practical benefits in terms of fitting into the built environment, maximizing capacity, and streamlining the waste collection workflow. It's a small detail that makes a big difference in keeping our cities clean.