Trucking serves as a barometer of the U.S. economy, representing 67.2% of tonnage carried by all modes of domestic freight transportation, including manufactured and retail goods. Trucks hauled 9 billion tons of freight in 2010. Motor carriers collected $563.4 billion, or 81.2% of total revenue earned by all transport modes.Said another way... trucking has inferior margins to the other modes of shipping (unless their profit margins are significantly better, and that is not the case), or costs the shipper more... which likely means that the shipper had no other choice... it then follows that "peak trucking" means "peak tonnage shipped".
It would seem to me that with the advancements in computer processing over the past several decades that the watered down version of the "traveling salesman problem" that comes part and parcel to the shipping (trucking) industry has been improved mightily over the past several decades, and that most of the inefficiencies that existed prior to said improved technology have been wrung from the system. The low hanging fruit has already been picked.
It will be interesting to see how that market rations available trucking tonnage with each passing year of decreasing availability.