I don't know about the laws in Portland, but in South Carolina a citizen can swear out a warrant on a driver who commits the infractions you have described. Depending on the jurisdiction, the local, county or state police will serve the warrant and bring the offender to trial. Of course, the citizen will be required to testify.

Before you go that far, you may want to talk to a police supervisor in your precinct. Ask for his or her oipinion before you decide what you want to do. My experience has been that the officers are usually aware of the troublemakers in their area. Cops tend to dislike people who behave in this manner on THEIR streets. They also tend to stand up for the underdog.

If this guy is already problematic, it may give the officers the PC (probable cause) they need to bust him. Further, if he has a criminal record or... even better... he is on probation for a previous offense, he could get in real trouble and you could pat yourself on the back for making the streets safer in your community.

It is unfortunate that we have to contend with people like this, especially when we're just trying to enjoy a nice, peaceful ride. However, it is always important for good people to stand up for what is right. We're not only protecting ourselves, but others who follow in our path.