Nearly zero of the freight rail network in north America is electrified: https://en.wikipedia.org/wiki/Railroad_electrification_in_th...

Sort of. The locomotives are diesel electric series hybrids. Which means you can make one that can travel anywhere that isn't electrified but add a pantograph to it for minimal additional cost and then stop burning diesel anywhere that is, and electrify the lines piecemeal.

Add a battery car and you only have to electrify a minority of the lines to be off diesel a majority of the time.

Extra points for electrifying steep grades.