Short answer: yes—it changes a few dimensions, but not every part of the bench has to be redesigned.
A typical street bench might have a seat height around 18–20 inches and a seat depth of 16–18 inches. For an ADA-compliant bench, the seat top should be 17–19 inches above the ground. That is the first dimension to check.
Seat depth is usually the bigger change. ADA bench guidelines call for a seat depth of at least 20 inches and no more than 24 inches. If your current bench is shallower than 20 inches, you will need to deepen it. If it is already in that range, you are fine.
Length also matters: the seat should be at least 42 inches long. Most full-size street benches are already longer than that, but small decorative benches may need to be scaled up.
If you add a backrest, make it at least 42 inches long and at least 18 inches tall above the seat. A backrest is not mandatory for every accessible bench, but it helps people with balance or fatigue.
Armrests are not required by ADA for all benches, though they are helpful. What matters beyond size is placement: put the bench on a firm, level surface next to an accessible route, and do not let it narrow the clear path.
So a safe target for an ADA-compliant street bench is: seat height 17–19 inches, seat depth 20–24 inches, seat length 42 inches minimum, and backrest height at least 18 inches above the seat if you include one. Local accessibility codes can be stricter, so use this as your baseline.