Discussion on NBC the first night mentioned the speed limits, and that the limit increases to 100 just north of the curve. It wasn't clear whether the 80 mph limit was all the way from Zoo or whether it was a step-down limit from a higher one further south. Again, we need an equivalent to a AP timetable for that line - anybody have one? Here's the only halfway decent reference I could find in my collection:

Trains did an extensive article on the NEC in April 2014. According to their map on p.29, the limits north of Philly are 60 or less for a while, then 80 for a short distance, then 110 & 125 between Frankford Jct. and Trenton. Their diagram, of course, is too small to show tighter limits at curves and interlockings. The ride-along (on an Acela, not a Regional) story in the article mentions a 30 mph limit until through Zoo, then 65 until 5 miles out of Philly, and 110 not starting until 7.5 miles out of Philly. Basically, nothing above 80 between Philly and the curve where the wreck happened.

Amtrak shares with both SEPTA and NJT in the segment between Philly and Frankford Jct., and with Conrail (?? in 2014? Maybe a Shared Assets area).