Does the trail continue after the 31st st. bridge north?
Yes, it continues "officially" as a temporary trail from the 31st Street Bridge to the Three Rivers Rowing Association building in Millvale Riverside Park. In this rather short segment, there is some loose gravel in certain areas but it is adequately packed down in most places. After heavy rains there are muddy areas but they have done a decent job filling them in rather quickly. If you have very skinny tires you probably don’t want to ride this section.
The trail continues from the Three Rivers Rowing Association to about a quarter mile north of Millvale Riverside Park. This segment of the trail is in great condition.
The trail then comes to an end and merges with the railroad access road and becomes the “unofficial” trail. This “unofficial” trail goes all the way to First Street underneath the 62nd Street Bridge. This section has varying conditions consisting of hard pack, loose gravel and some heavy gravel. You do not want to be on this section with skinny tires. This section frequently has railroad workers but the access road is more than wide enough to stay clear. I wave to them every day and have never experienced any problems.
Can I get to the Highland Park Bridge?
Yes - Once you get to the 62nd Street Bridge the "unofficial" trail ends and you can take Main Street to the Highland Park Bridge.
FYI - I ride from Sharpsburg to Gateway Center every day using the above route. My mountain bike does not have fat tires but they aren’t skinny either (more skinny than fat - not sure of the size) and I have no problems.