What are the rights regarding those who use a public road that resides on private property?

This just happened. A police officer came to my parents house about a speed bump that is on a public road on a neighbor’s private property. We live in a heavily wooded valley in Washington state. The speed bump was made by that neighbor because of one family that lives around us that drives really fast.You are supposed to go about 10 mph due to children, animals, etc.

Essentially what happened is that after three years of having a gradual ease into the speed bump using gravel that neighbor has decided to take out all the of gravel leaving a high and sharp bump. My dad has been putting the gravel back in because it hurts the neck and back when you go over it at any speed. He’s done this three times and this time they called the cops on him. There is an issue with harassment with this particular family. A very long history and we don’t provoke them in any way. We just stay away from them. What is need to know is if there is any actual legality behind this and if there is any law that I can look to. I’m only looking to protect myself, not start any fights.