how busy was the lehigh valley route that went to niagara falls?
Depends on what era you are thinking of.
Towards the end of the LVRR there were two trains/day, one east (COJ-32) and one west (NE-1).
On Tues-Thurs-Sat there was also the Tift Terminal-Suspension Bridge local, commonly referred to as the "Crosstown Pickup" (TTN-2 & NTT-1) which was a turnaround job.