> If the US were to invest in running the railroads efficiently, getting a package from NYC to LA in less than 72 hours should be possible

Still need air for every other pair of destinations. And in the meantime, I’d be shocked if that freight leg had enough volume to justify that expense over a couple more planes.

I think freight trains in Europe are much faster than in the US, but also much shorter (though there are plans to make them a little longer) and lighter (no double-stacked containers). So they are more costly but you get stuff from A to B faster.

Electrified locomotives are better than diesel electric (e.g. an electric locomotive has 2x - 3x the power, ~6MW-9MW compared to ~3MW, so you need less locomotives, less moving parts means less maintenance etc.), but while it works in dense Europe, it's too costly to build and maintain cross US.

US freight rail companies have already invested heavily in efficiency and are now pretty much the most efficient in the world. What you seem to be asking for is a reduction in latency. You can't have both high efficiency and low latency: those metrics are in direct conflict with each other.

Trucks with team driving can already run coast to coast in about 3 days. This works fine for somewhat time sensitive loads.

72 hours is too long. You need 48 hours or less for e-commerce or you’ll lose business to Amazon. You could go multiple warehouses but that’s a huge expense with splitting inventory especially if you have lots of low volume skus.