On the country's busiest MUP, the West Side Greenway, there are sections too crowded to ride fast with too many road crossings, and sections that are straight and less crowded. But this is NYC in general. And does the type of trail matter in how many miles you ride? In fact I do a large percentage of my miles in Prospect Park, which has 3 lanes all closed to traffic. Is this now a MUP because there are no cars? The speed limit is 25 but other than the small downhill you won't exceed that anyway. Nah, it doesn't matter where I'm riding. If I'm riding my road bike they are road miles. If I'm on my commuter they aren't road miles, but they are still miles. If I'm out with my wife and/or family, it is a slow meandering ride but they are still miles.