As a visitor to Eugene on numerous occasions and from the mountain bike town of Sedona I can give some insight. Eugene's Trail infrastructure is far too small for the number of residents and visitation the town sees especially in comparison to the transportation and commuting infrastructure for bicycles. Increasing the trail opportunities will disperse the users and benefit everyone. In adding to the trail system careful design and construction with good site lines, proper use of in slope and out slope etc. you can mitigate most trail conflicts. That said you can never expect to eliminate the human factor as in there will always be idiots on foot, on bikes and horses. That said the nature that the trails are constructed in Eugene (the few that there) sets the stage for high speed and out of control cyclists. No obstacles, long straight aways, sharp corners and gravel make for higher than normal speeds even for beginners(who you should be worried about). BTW Sedona has close to 300 mi.