US on-highway diesel has pushed past $6 a gallon, and the reason matters more than the number. This is not a crude-led move: it is a distillate move. Houthi control of the Red Sea corridor has pushed Gulf and Indian diesel cargoes onto the long route around Africa, the drone strike that shut a Saudi pipeline removed the one route designed to bypass Hormuz, and Russian refining remains impaired. Distillate, not crude, is the scarce barrel, and distillate is what moves American freight.
The freight consequence is a shift in a threshold that most people treat as fixed. Intermodal carries a structural penalty that rail line-haul does not: a truck drayage move at each end, a transload, and an extra day of transit. That penalty is roughly constant in dollars regardless of distance. The fuel saving, by contrast, scales with distance, because a train moves a ton of freight about four times further per gallon than a truck does. So the crossover distance at which intermodal beats truckload is a function of the diesel price. At $2.50 diesel the crossover sits somewhere around 700 to 800 miles, which is why US domestic intermodal is essentially a transcontinental and Chicago-to-Southeast business. At $6 diesel the same arithmetic drags the crossover toward 500 miles, and that is precisely where the densest American freight lanes live: Chicago to the Southeast, the Ohio Valley to the Northeast, the Southeast to Texas. The addressable market for intermodal does not grow linearly with diesel. It steps.