Dang, caught me sleeping in -- you did! I've mentioned this before, but here goes again. The trail north from Millvale is owned and maintained by Norfolk Southern RR. It parallels the track that you cross/pass pass under as you enter Millvale Riverfront Park from Route 28, and acts as a service road for NS maintenance vehicles.
As I understand it, if a property owner permits free access to or across their property for an extended period of time, to the point where people ASSUME they have a right to be there, the property owner has created an easement, although one that is not protected by any terms or protections. Therefore, NS is being as accommodating as they can be of cyling on that section of trail, while also continuing to assert that these riders are, in fact, trespassing on private property. In so doing, they are protecting their corporate property rights.
I believe that Friends of the Riverfront or other group is in discussions with the railroad to address these issues and perhaps work out an agreement that would extend the trail northward. It may take some time, that's all.
It would be sweet......