Bicyclists are encouraged to use the *CSP hotline to report aggressive drivers to the Colorado State Police (just dial *277 on your mobile). You must obtain the license plate of the vehicle and describe the aggressive behavior. Location, direction of travel, and a driver description are good too, but not mandatory. After 3 reports of the same vehicle, the registered owner gets a warning letter. Subsequent reports will result in a state trooper visiting them in person and taking “appropriate enforcement action”, whatever that means. If you’re not on a state highway, make sure you get them to enter the info into the database before you’re transferred to local law enforcement to make a report. Hopefully they’ll make some kind of annual report as to what actions this system has actually resulted in.