Why Do Sidewalks Have Built-In Cracks in New York?

https://kingspavers.com/why-do-sidewalks-have-built-in-cracks-new-york/

If you've ever looked down at the sidewalk in front of your building and noticed a series of straight lines running across it every few feet, you may have wondered whether the concrete is falling apart. It usually isn't. In most cases, what you're looking at is a control joint, a groove intentionally cut or formed into the concrete. So to answer the question directly: why do sidewalks have built-in cracks? They don't, technically. What looks like a crack is almost always a planned joint, placed there specifically so the concrete has somewhere to move without breaking apart on its own terms.