I remember, several years ago, while riding a rail-trail (ironically-in PA), my wife and I noticed 2 males on bikes which didn't fit them at all, riding a short distance behind, but not overtaking, an attractive female runner. We turned around and followed the 2 on bikes. We stayed far enough behind, but close enough so they knew we were there. We rode along behind them until the runner got into her car on a lot along the way. Bad intentions?-we'll never know, but we do know the runner ended up safe. You just never know. I would imagine now that most ride with a cell phone-so if something looks out of place, it can be reported, should you see it coming.