Funny, the "Heritage" sleepers were classified as lightweights when they first came out. I think a heritage sleeper weighs about 60 to 65 tons each (somebody correct me if that is wrong) and the older standardweights that preceeded them tipped the scales at something north of 80 tons, and usually, always I think, rode on six axles instead of four.
The heritage sleepers were built from the mid 30's to the end of any purchases of passenger equipment by the railroads, which was about 1964. The older heavy weights were mostly built in the 20's or somewhat earlier, back to the time of the ending of consruction of wooden passenger cars. I do not know when that was.
Yes, 1000% as Mr. Harris says, heritage cars were, indeed lightweight cars. They were also called "streamlined" cars.
To find true heavy weights you have to go to the generations preceding that. the last heavyweight cars were constructed in the mid-40's and just a few at that. I think just one railroad ordered about 15 heavyweight coaches or maybe it ws sleepers after WW2 and I do not remember who that was. By that time, everything else was being ore ordered as streamliined. There was a small overlap between the beginning of lightweight construction and the curtailing of heavyweight. Amtrak has never even touched, even looked at a car which was not lightweight. It never had heavyweight cars.
To try to picture heavyweight cars, think about, maybe, the Polar Express (look at the roof) . Think also of old western movies with steam engines, the cars they were pulling were examples of heavyweight --not anything Amtrak has ever, ever owned. Even heavy cars like The old Santa Fe hi-level cars and Amtrak superliners are still considered lightweight, yard per yard, due to their lightweight construction, their obvious bigness notwithstanding.
In fact, lightweight cars were usually stronger than heavyweight, esp. if bult of stainless steel. Stainless steel was most often how lightweight streamlined cars were built. Some were painted, some were left as silver. Stainless steel is less corrosive, also. Some streamlined cars were built of aluminum alloy.
The superiority of lightweight streamlined over heavyweight is sort of like the comparison between steam and diesel. Steam makes all the noise, got the publicity etc but diesel is quiet and efficient.
In fact, diesel power and streamlinng(i.e. lightweight construction) sort of came along at close to the same time, late 30's early 40's. Construction was halted during WW11, but then diesels started growing on trees thereafter and many lightweight streamlined cars built also. (though streamlining never became as prevalent as dieselization).The electric locos of the northeast are separate from a discussion of steam vs. diesel.
Amtrak has always wanted to convey a contemporary/modern image--not a nostolgic trip. Amtrak would not have bought heavywieght cars any more than it would have bought steam engines!!
Llast but not least, the stainless steel equipment on the Canadian is indeed lightweight and streamlined- as well.