The horizons are good for 125mph operation and have been used on NEC trains. They were axle counts cars needed for the test since one Viewliner and one ALP had the trucks cut out (meaning no brakes on that truck) because they had the instrumented wheel set taking measurements. The 54557 didn't even have HEP. They just used it because there are a few PTC test trains roaming around as well. Plus, the ACS test train is floating around as well as a few training trains.
This is off topic, but I have no real place to stick it and it ties into the lack of equipment. If you live along the NEC, be advised the yearly Conrail excursion with the E-8s that crisscrosses NJ is operating this Saturday. It will be on the NEC between PHL and NWK early in in the day. It will then back to the Lehigh Line and plod around such places as Croxton, the old Chemical Coast District, Amboy Secondary, Freehold. The highlight in my opinion is the journey down the old Chemical Coast district to Wood interlocking on NJT's NJCL, where it will operate across the Raritan River Swing Bridge. There are 4 Amfleets tagging along with their usual compliment of cars in the old Pennsylvania railroad varnish.