That's a great and practical question! It really depends on the specific design and location of the trash can. In most modern urban settings, especially in public parks, sidewalks, and transit areas, the lids are typically permanently attached by a hinge, chain, or integrated mechanism. This is a standard safety and design feature. Attached lids help control odors, prevent litter from being scattered by wind or animals, and deter people from rummaging through the bin. They are usually made from durable metal or heavy-duty plastic and swing open on a fixed point.
You might find some older models or bins in less formal settings where a lid can be lifted off completely, but this is becoming less common. Municipalities generally prefer attached lids to prevent loss, vandalism, and to maintain a cleaner appearance. So, while you can almost always open the lid to throw something away, you'll rarely find one meant to be carried away separately. The design prioritizes function, hygiene, and durability for public use.