That's a great and practical question! It really gets into the details of urban design that most of us don't think about. So, is the interior of the average city trash can smooth? The short answer is: ideally, yes, but it's not always perfect.
In modern public waste management, the goal is absolutely to use materials and designs that are easy to clean and maintain. Most contemporary public trash bins, especially the larger, stationary ones you see on sidewalks, are made from molded plastics like polyethylene or from coated metals. These materials inherently create a relatively non-porous, smooth interior surface. The reason is straightforward: a smooth surface prevents waste, particularly liquids and sticky substances, from adhering easily. It allows for quicker hosing down, scrubbing, and disinfecting by sanitation crews, which is crucial for controlling odors, pests, and bacteria.
However, it's not always a flawless, glass-like finish. Some bins might have textured surfaces for added structural strength or to hide scratches. Older metal bins, if the coating is chipped, can have rough, rusty spots. The very act of people throwing in bags with sharp edges can create grooves and scratches over time where grime can build up.
So, while the design principle strongly favors smooth interiors for hygiene and maintenance, the real-world condition can vary. A brand-new bin in a well-funded district will likely have a perfectly smooth interior. An older, heavily used bin might be more challenging. The focus for cities is on choosing materials that start smooth and are durable enough to stay that way, making the crucial job of cleaning as efficient as possible for public health.