At one time, both of the locomotives shown here were the top of the line passenger locomotives for their respective railroads. But like many technological advancements - they too get replaced. For the PRR 3750, its passenger hauling days were toppled by the arrival of the first generation E and F units on the Pennsylvania Railroad. For the Amtrak E60 #603, it was the locomotives inability to be as universal as engines such as the AEM-7 and HHP-8. Today, they stand as relics to a by-gone era in railroading. Perhaps in due time - they'll be joined by more 'technological marvels'.