When planning an urban bench, the most important clearance is right next to it. I usually recommend leaving a clear, level space of at least 30 inches wide by 48 inches deep beside one end or along one side of the bench. This is the standard wheelchair space dimension used in ADA guidance, and it lets a wheelchair user pull completely out of the walking path while sitting beside a companion.
Don’t forget the path itself. An accessible route should be at least 36 inches wide, so if the bench sits along a walkway, keep that 36-inch clear width behind or in front of the bench. A bench placed too close to a curb, planter, or railing can force wheelchairs into traffic or rough ground.
If your site allows it, try to include a 60-inch diameter turning area nearby, or a T-shaped turning space. That makes it easier for someone to approach, turn, and leave without reversing long distances. The surface under and around the bench should also be firm, stable, and slip resistant—pavers or concrete are usually fine; loose gravel or heavily sloped ground can make access difficult.
In short, aim for a 30-by-48-inch clear companion space at the bench, keep 36 inches of accessible path clear, and add a turning area when you can. Those numbers cover most urban bench installations and make the space feel welcoming rather than tight.