Short answer: yes, most well-made urban benches are both sanded smooth and sealed—but that doesn't mean every bench you pass is safe. The finish can wear down, weather can lift the grain, and older or low-budget benches may not get the same care as a park centerpiece.
When a wooden bench is built for public use, the slats are usually planed and sanded in stages, often up to 150 or 180 grit on seating surfaces. That removes loose fibers and rounds the edges enough to prevent most splinters. After sanding, the wood is typically sealed with a protective coating. Common options include polyurethane, spar varnish, exterior-grade paint, or penetrating oil. These sealants lock down surface fibers and add a weather-resistant layer.
That said, real-world conditions matter more than the original workshop finish. Sun, rain, freeze-thaw cycles, and heavy use slowly degrade the sealant. Once the coating cracks or wears thin, moisture gets in and the wood grain can swell, split, or become fuzzy. That's when splinters become a real risk. Benches made from softwoods like pine or fir are more likely to develop rough spots than dense hardwoods like oak, teak, or ipe.
So how do you check before you sit? Run the back of your hand lightly over the seat if you're unsure—your knuckles are more sensitive to rough fibers than your palm. Look for a continuous, intact finish, not flaking or chalky patches. If the wood appears gray, cracked, or fuzzy, treat it as unsealed and sit with a layer between you and the bench, or choose another spot. A quick visual check is usually enough: smooth, satin or glossy slats are generally fine; dull, splintered, or raised grain is not.
For city managers and designers, the safer long-term strategy is to use naturally smooth hardwoods, add regular sanding and resealing to the maintenance schedule, and consider recycled lumber or metal slats in high-wear areas. But for everyday use, the answer to your question is reassuring: a properly maintained urban bench should not splinter because it has been sanded smooth and sealed. The key word is "maintained."