Complex sentence: Amtrak ordered 15 HHP-8s in 1996, at the same time as the order for the "Acela Express" trainsets; the locomotives have similar external styling as the Acela trainsets, but are designed to operate as true locomotives, hauling conventional passenger rolling stock.
Split into simpler sentences: Amtrak ordered 15 HHP-8s in 1996 at the same time as its "Acela Express" trainsets. The HHP-8s have external styling that is similar to the Acela trainsets, but are designed to operate as independent locomotives, hauling conventional passenger rolling stock.