That's a great question about a detail many of us walk past every day! In my experience, it really depends on the specific city and its public works department. Many standard public street bins do not come with permanent, built-in plastic liners like you'd use in a kitchen can. The primary reason is durability and maintenance. These bins are designed for heavy, often rough use, and a fixed liner would tear quickly, creating more waste and requiring constant replacement.
However, that doesn't mean liners are never used. You'll often find heavy-duty plastic bags or liners inside bins in high-traffic, high-waste areas like tourist spots, parks, or outside major venues. These make it drastically faster and cleaner for sanitation crews to empty the bins—they simply pull out the full bag and drop in a new one. Some modern "smart" or solar-compactor bins even use custom-sized liner bags as part of their system.
The alternative in many cities is a regular cleaning schedule. Bins are emptied directly into the truck and then pressure-washed or steam-cleaned on a routine basis to control grime and odor. So, while your kitchen trash can relies on a bag, public bins often rely on robust design and frequent, thorough cleaning. The goal is always the same: keeping our cities cleaner and more hygienic for everyone.