Indeed a great system, but oh so expensive...

There's a train line close to me which runs on tracks parallel to a freight line.

The company maintaining the latter was asked several times if their infrastructure could be used, but they refused each time, so the passenger line, which was always there, just in a state of disrepair, had to be refurbished at great expense.

I'm happy with the result though because like in every track having just one line, the trains are amazingly punctual.

And if you’re going to pick one, there are plenty of reasons to pick freight. A single freight train might have 70-200 cars, each of which can carry 1-2 full-size intermodal containers (if not a comparably massive tanker car or something). Trains are more efficient than road vehicles in terms of energy consumption, wear and tear on the road (or railroad), and labor cost, but these efficiencies scale up considerably based on vehicle weight, and the weight of a few hundred loaded intermodal containers is a very high number indeed. Not to mention that intermodal containers are a lot less fussy about hospitality than passengers!