A long exposure works because most people don’t stand in one spot for more than a few seconds, so the camera doesn’t capture them. For them to be captured, they would have to stay in one spot the entire time you are taking the photo. You will notice a little ghosting of people that stood a little longer. If it’s a high traffic area, take a couple of shots and fix it in Photoshop.

Want to learn more? Check out this article, “Easily Remove People from a Photo”