I don't think the table would include tonnage of empty cars. When one talks of "number of carloads" a line hauls, it is loaded cars, empties don't count.
If the Grande could divert all the traffic to Motorway trucks, they would do so. But they had only so many trucks.
Lumber was sizable commodity late in the game. There were mills in Durango, Juanita & Chama. In the last months of 1967, there were a few trains that went from Alamosa to Chama and back. There was no traffic west of Chama. There was a spell when no trains went to Durango for a month.