I gave up on "on your left, or "passing" and just yell "Behind ya" from way back. If they look sketchy or have kids I just slow way down. Last year 80 yr old women was stuck and killed by a 56 yr old rider on my favorite MUP. A week after that the town Mayor was on the trail and was hit too. Now half the trail has a 10 mph speed limit. If I really want to hammer I ride roads or accept what I am dealt on the MUP.