Driving too fast in the park

How do you prevent people from driving too fast in the park? My manager says he has talked to people until he is blue in the face. We have gravel roads. Driving fast cause ruts which erode the road. I suppose we could hand out violation notices but I’d have to evict half the park. Charge a fine or “repair bill”? Most will ignore a $10 fine and just pay their rent. Has anyone seen removable speed bumps that don’t tear up a gravel road? Would have to take the bumps out for plowing in the winter.