Truck MPG

The Obama administration is looking to make the nations trucks more efficient, requiring a 20 percent cut in emissions in model 2018 trucks. (Source: Bloomberg)

The work trucks covered by the proposal make up 4 percent of U.S. vehicles while
accounting for 20 percent of the oil consumed, according to the Union of
Concerned Scientists, a Cambridge, Massachusetts-based environmental group.
Long-haul tractor-trailers get about 6.5 mpg, the group said

MGP measure how FAR a truck can go on a gallon of gas, but a much better metric is how many ton-miles (or how MUCH) a gallon of gas will produce.

This study has the following:

Trucks: 250 Ton Miles
Rail: 437 Ton Miles
Barge: (local waterways) 545 Ton Miles
Ocean Cargo: 574 - 1050 Ton Miles (depending on the size of the ship).

Since trucks account for about 70% of all cargo shipment volume, minor increases to the ton-miles of trucks will greatly reduce oil consumption and CO2 gasses.