I had occasion to view a couple of Cass Trucking Index graphs, both for shipments (the physical volume) and for expenditures. Interestingly, the number of shipments in 2015 is almost dead flat compared to 1999.
Since US population has increased by over 15% during that time, from 279 Million to 322 Million today, I would have expected a similar rise in shipments.
Of course, 1999 was before the Bubble burst, while today we have anything but a robust Economy. Even so, with our political leaders trumpeting all the strides they have made to get the Economy back on the right track, dead even compared to 15% higher betrays an Economy that still is worse off than 16 years ago.