AFAIK it’s illegal for a neighbor to change to flow of water to cause it to come onto your property. I’m guessing that a “road association” is some sort of quasi-governmental agency on the order of a homeowner’s association. Even so it may be illegal for them to “take” your property in this way. Last week’s Supreme Court ruling notwithstanding.
You need to trot down to the (city? county? township?) surveyor’s or code enforcement office and find out who put that culvert in.
We recently had our lot surveyed in North Conway, New Hampshire. The surveyor concluded that “there is a culvert that has been recently installed which is causing an extraordinary amount of drainage onto your lot. This drainage makes it tight to put a septic system on the lot while adgering to NHDES setbacks from property lines and water courses”. Also, a Wetland Scientist has now deemed the lot wetlands and “unbuildable”. If this culvert was put in place by the road association or perhaps by a neighboring lot, is it legal to direct that water source onto our property?