The comments for the 500th post were put into a hat,
My answer to the question was California State Route 1, also known as Pacific Coast Highway, Cabrillo Highway or Shoreline Highway. While most of the route is maintained like any other road; the stretch from Northern San Luis Obispo County to the City of Carmel is under constant maintenance. After each rainy season debris from above comes falling on the road or parts of the road disappear into the ocean. While the original construction costs may not have been large the ongoing maintenance costs are quite large. Most of the terrain in the troublesome stretch looks like this.