That's an excellent and practical question. There isn't a single universal number, as the ideal count depends on several factors specific to your downtown's layout and usage. A common baseline recommendation from urban planners is 3-5 bins per standard city block. This serves as a starting point, but the real answer comes from asking more questions.
First, consider pedestrian volume and flow. A block with a major transit hub, a popular park, or dense restaurant patios will need bins at both ends and possibly in the middle—potentially 4-6 or more. A quieter, primarily office-based block might manage with 2-3.
Next, think about placement and visibility. Bins should be positioned at natural stopping points: near crosswalks, transit stops, building entrances, and food vendors. The goal is to have a bin in sight when someone needs it, preventing littering. They should be on the path of travel, not hidden in an alcove.
Capacity and maintenance are arguably more critical than the raw number. A single overflowing bin is worse than having one less bin that is emptied regularly. High-traffic areas may need larger capacity or even solar-compacting bins. The schedule must match the generation of waste; evening emptying is crucial in dining and entertainment districts.
Finally, consider bin type and purpose. Separating recycling and organics? That might mean installing dual or triple units at key spots, which counts as multiple "service points."
My final recommendation is this: Start with a pilot of 4 bins per block—one at each corner. Then, monitor them. Are they constantly overflowing? Add one mid-block. Are some consistently half-empty? You might adjust. The data from your own streets will guide you to the perfect, efficient number for a cleaner downtown.