I know that a handful of these cars are (maybe?) still used for thing like toilet paper, according to what I've read here. Back when these were mostly used for auto parts, they would not have seen a hump very often. On the SP these and auto racks made up APW's and APE's and loads and empty's in LA originated or terminated from the Gemco and Tweedy and Tweedy GM plants. There is no reason, except maybe with "short' squeezers on the older humps that you couldn't necessarily hump these cars, it just wasn't necessary.

As I recall, these long box cars, mostly carried frames and exterior parts like hoods, fenders, trunk lids, which were spotted and pulled directly from the tracks adjacent to the assembly line, where they were spotted by the parts being used on that section of the line. There never was a reason to "hump" them in LA to make up blocks "classified" them by "destination", and there was no hump at Gemco or Tweedy, so all of these cars were switched.

SPHS&TS Quarterly just had a great little article on Gemco, which might help you answer more questions. I worked mostly out of Tweedy, but earned many an extra days penalty pay for running "hot" cars, from the Shops out to Gemco, even up to the last month I worked. If didn't get all the parts necessary to spot the plant, you'd shut down the line....and hottest trains I've ever run were "shut down" trains. including once with just 3 units, 4 "hot" cars, and a caboose, with an RFE telling me that there were no speed restrictions......, and I made Yuma to Indio in under 2:20, switch to switch.......not very likely something ever said or done in today's safety culture.