(Portland, OR)  --  It appears most charges of evading fares aboard TriMet transports won't be enforced.  Prosecutors in the TriMet service region are citing a Portland State University study that found minorities are disproportionately affected.  According to "The Portland Tribune," a ridership survey found minorities were more likely to ride without tickets, and were punished at a higher rate.  District attorneys say they'll no longer prosecute Interfering with Public Transportation cases, except for those that involve physical and other threats.