miles of track per square mile, or alternatively, miles of track per square mile of population above N-per-unit-area would be a much more meaningful statistic.

I'm not sure population is too important here, that stat would just make dense countries look 'better'. In reality if you want to ship something from California to DC by Rail, it really doesn't matter that 95% of those 3000 miles have almost no one living nearby.

We're talking about Semi Trucks here, so clearly this conversation is in regards to cargo.

Hence my second proposed statistic.

"3000 miles of track to service land holding 60 million people" vs. "100,000 miles of track to service land holding 50 million people".

(the numbers are invented, not real)

Hence my first proposed comment, "that stat would just make dense countries look 'better'".

The U.S has a lot of empty land, so this would just be a manufactured stat with arguable meaning.

No, it wouldn't because the only land that would "count" would have more than N people per square mile. So in the US, North Dakota would barely count for anything.