Sad if your local police will not be helpful. I have used local PD to get a couple of drivers convicted in a court. It is a 50/50 chance depending what cop gets the initial dispatch.
Maybe try your state police. Colorado State Patrol has a web page to report drivers. About 3 reports and the driver gets a talking from CSP. Have a video and some drivers get ticketed and others arrested.
Mount a camera on your wrist. When someone is approaching close, hold the camera out so the driver can see it. Often gets a quick lane change or hard braking before they reach you.
Check public records information. I can go on a judiciary web page for my state and look up traffic infractions associated with a license plate. Any tickets to that plate # gives the name of the driver and a link to other infractions from that driver. Go to
https://www.familytreenow.com/ and you can often get an address and phone #. I have called a couple of drivers letting them know that I have video and any further harassment or endangerment leads to a police report or civil action.
Some drivers live in my area and I can often cycle by their house. That lets them know I am a nearby neighbor and that I know where they live.
Post bad driver videos on facebook and youtube and include the town name for searches. Pass videos of the worst drivers and facebook/youtube links to your local news. They may run a story for a really good video on a slow news night to fill air time.