If you think longer-term, electric trains are realistic. If batteries are cheaper than Diesel, you could just put 2x20ft container at the front with batteries.

If you think longer-term, electric trains are realistic. If batteries are cheaper than Diesel, you could just put 2x20ft container at the front with batteries. They can be swapped en-route and used as battery storage when not in use. As far as I know, most newer freight trains are diesel-electric anyway so not sure if you couldn't just feed the electric engine directly from a battery without buying new engines. Currently not feasible because of high battery prices but realistic in 1-2 decades. And losses are lower than for electrified rail. Busy routes are still better electrified but the huge US freight rail network would likely be cheaper to convert that way.