Honestly, my short answer is yes—sometimes, and often pretty well—but they're not magic. An ashtray-topped trash can works when it makes the right behavior easier than littering. If someone finishes a cigarette near a bin, they're much more likely to use it if there's a visible, well-marked spot to stub out the butt. That keeps a lot of cigarette ends out of gutters, planters, and ordinary trash compartments, where they can smolder or make a mess.
But the design only does so much. In cities, the biggest problems are maintenance and placement. If the ashtray is full, overflowing, or gross, people stop using it. They either drop the butt or shove it into the regular trash slot, which can create smell and fire risk. So the bin has to be emptied often enough, and the ashtray part needs to be cleaned separately. Rain, wind, and vandalism matter too. Cheap plastic or poorly angled tops can collect water or let butts blow out. A good model has a deep, angled opening, a metal or fire-resistant liner, and a way to empty it without mixing butts with recyclables.
Placement is just as important. These bins work best outside bars, transit stops, office entrances, and smoking areas—places where people naturally pause with a cigarette. Putting one on a quiet residential corner won't do much. Signage helps, too, but it should be simple: a small "butts here" label or a visible stub-out plate is better than a big lecture.
Do they actually work well? Yes, compared with no ashtray at all, they can noticeably reduce cigarette butt litter around the immediate area—if the city services them. When they're ignored, they become another overflowing bin and people lose trust in them. So I'd call them a useful tool, not a standalone solution. They work best as part of a broader approach: frequent cleaning, smart placement, fire-safe design, and maybe public awareness campaigns. In short, an ashtray trash can is only as good as the maintenance behind it.