From Jeff Ellerbusch:

This afternoon I went to check on the Cliff Swallow nest on the 287 bridge over the Raritan in Franklin Twp (see the 6/25 post). The nest on the north side of the bridge, the previously active one, was inactive…however the previously empty nest on the south side of the bridge was very active. The pair was constantly in and out of the south side nest- one of them would sit in the nest while the other would occasionally come in to feed it, every once in a while the birds would both go in the nest for a minute or two. The only conclusion I could come up with is that the pair is in the process of making a second brood, which this time will be in the south nest. Every so often a juvenile from the first brood would accompany an adult to the nest and try to get in but would immediately get kicked out, it would then cling to the side of the bridge and wait for an adult to fly off at which point it would follow. The adults paid the juvenile no attention… harsh.

The only practical way to see the south side nest is to park at the lot off Easton Ave and walk the very short walk to the bridge on the towpath (Google Maps) 40.540441,-74.514105

Jeff