It's Thanksgiving weekend, and today is "black Friday", and there is a normal seasonal cycle of import peaks and valley's, as Christmas comes at the same time every year, and summer/fall is still the predominant harvest season, so the need for things like stacks also varies by season.

This quarter and the last saw bigger of volumes imports, because of tariff threats, folks like those who import consumer products, or production inputs, from Model RR distributors, to auto manufacturers have been on a buying binge. This, has had the effect of pushing up imports and the import deficit over exports, to beat this "tax increase" on those imported goods, while tariff threats and the imposition of "real" tariffs, and retaliatory tariffs have tanked demand for US agriculture exports, for the last year.

I would worry more about low labor productivity growth, and the significant total Investment in the US economy, which is down significantly, with direct foreign investment down nearly 80% in two years. GDP=C+I+G.... C=total consumption, I=total investment, G=government spending. A fall in I reduces short term GDP due to less investment in plant and equipment (which uses labor and output from other sectors). but which reduces future growth rates, as well. It is a sort of "two-fer" economic negative, especially when we have such low labor productivity growth.

The best example of the economics of car storage are in tank cars and fracking sand hoppers.
Oil at $75 a barrel=lots of cars in use, oil at $45 a barrel=lots of cars in storage, as many may have noted over the last two years.

You may be seeing empties headed to storage simply because it is the end of the peak demand period.

Here is what you really need to look at:

AAR Carload Data Charts