Reporting an Unsafe driver to Motor Vehicle
In addition to reporting drivers to law enforcement, you may also be able to report an unsafe driver to your motor vehicle agency.
Many Motor vehicles do have some kind of program for unsafe drivers. They are called Driver Re-evaluation Programs. Most of them are meant more for reporting people that are no longer able to drive due to some kind of medical condition. The DMV may reexamine a driver if there is evidence that suggests they may not be able to drive safely. This could include observations from family, friends, physicians, or law enforcement. It is not necessarily intended for reporting strangers who are caught on dashcam videos observed driving in an unsafe manner. However, there are a few states that do allow you to submit dashcam videos of unsafe drivers to their motor vehicles.
If not the motor vehicle in your state may have an email address for help or general information questions. It might be possible to contact them and report a driver that way.
If you do find someone willing to help, you can ask them to mail the vehicle owner a warning letter or suggest the driver take a safety course.