The Rails to Trails bike paths fall into two categories, what I call "Inner City" and "Country". "Inner city" bike paths are used as much as by walkers as bikers. They are heavily used, I end up tying to avoid them when biking do to the high number of Pedestrians (and when I do bike on them I go slow around any Pedestrians I come across). When possible I bike on nearby roads. These trails tend NOT be be design for HIGH SPEED biking, if you want to go over 10mph you better go by any nearby road then the bike path.
As to "Country" paths, these also tend to be used by hikers, but since the number of people on them is less, a bicyclist can go a faster pace (But must still slow down around people on foot). In the Mountains where I live, the bike trails are the best way to bike through the mountains (The old Railroads tend to go up very gradual grades). These grades tend also to be quite long and thus most people do NOT hike them (Through you still have to watch them). Thus it is possible to go over 10 mph on such "Country" paths, but you have to slow down when you are around other people Even on "Country" Paths.
One last comment, the "country" paths tend to be wider (in my opinion) then the "Inner city'" trails, just na observation. This may be do to the lower volume of people on "Country'" paths as oppose to "inner city" paths, but reinforce the need to go slow when passing other people on the trail.
For more on the Giant "TCR" bikes see:
http://www.giant-bicycles.com/en-US/bikes/road/One last comment, Pennsylvania used to have a Law that if a Bike path was near a road, Cyclist HAD to use it. This was repealed about 15 years ago right after an accident where a high speed cyclist hit and killed a pedestrian on a bike trail (This was NOT a rails to trail line but one built along a road in a Count Park in Allegheny County called "South Park". The trail was design by people who assumed that bikes were low speed vehicles and thus could mix with Pedestrians on a trail with lots of ups and downs as while as curves. It was a bad design for a Bike Trail and ended up getting someone killed. It is now a walking trial with low speed bikes permitted don it, high speed bikes go on the nearby four lane road with the Motor Vehicles.