Automobiles are easier to scale until you hit a brick wall. Subways and trains can transport a lot more people than roads. A subway line with modern signalling can have a train every 45 seconds or so. It's impossible to match that with normal roads. Dense cities can't function without trains. Imagine London, Tokyo, or New York without the subway.

1. Yes trains in very dense areas or connecting dense areas make sense - that's why my comment says "nearly all" trains

2. Everywhere else, even in dense cities, cars are very good at delivering people from where they are to where they want to go, without a large investment in single-purpose facilities like passenger railroads.

Especially in the US, it makes almost no sense to send passengers on rail when it would be more time efficient to fly between dense areas, and use the railroads for transporting freight - a task where they excel.

I'd argue that in dense cities cars are about the worst mode of transport for able-bodied people. For almost all trips a combination of a bicycle and a train is faster. Cars are expensive. Cars pollute. Car infrastructure, especially parking, consumes valuable living space. Cars cause deadly accidents.

All those things are true, but you must balance the bad against the huge good - cars are effective at moving people around the city and to the suburbs.

Is there a source on that? I would expect an electrically propelled train to be extremely efficient from an emissions standpoint and to have far far lower emissions when occupied, enough to offset running a few empty ones.

If you look at the operational emissions, this is true. Infrastructure does however play a role. Planes have high operational emissions but require little infrastructure. Trains have little emissions but require enormous infrastructure.

It's however completely unclear to me which CO2-calculators account the infrastructure, and which do not.

The cost of infrastructure is extremely hard to quantify. Roads aren't free either, and parking in cities makes them less dense and hence increases the distances people need to travel.

Where does the CO2 cost of the infrastructure come in? Is that just in construction or do rails somehow emit CO2? Or are you just saying that rails take up space and that's an environmental impact too?

I feel like I'm missing something.

I’m guessing it is in the production and transportation of materials to the site. Subway stations require a lot of material to build, so you’d have the CO2 cost of the concrete, rebar, etc... rail lines don’t have much material, but producing steel does take a lot of energy. And if the line is between large metro areas, the rails would need to be transported to (potentially) remote areas.

But I’m guessing that in terms of CO2 impact, these are fixed costs. So, it would seem reasonable to me to assume the operating CO2 costs would dramatically outpace the fixed initial costs, hence why it would be ignored.

Or potentially, when comparing two systems, the initial building/infrastructure CO2 costs may be assumed to be roughly equal, so are factored out.

The German newspaper article names construction and operation of railway stations, and the construction of the infrastructure itself.

My main point is: there seems to be a non-neligible impact, and CO2 calculators don't help me grasp that.

Is the German newspaper also considering the infrastructural costs of road construction, expansion and maintenance (particularly maintenance costs incurred by shipping freight on those roads instead of rails)?

Forget newspapers. Here's an IRU study about combined rail/road freight transport accounting for costs and emissions.

"There is no such thing as a truly environment friendly means of transport. Combined transport is not inherently superior to pure road transport in terms of environmental impact, as measured by energy consumptionand CO2 emissions."

https://www.iru.org/apps/cms-filesystem-action?file=PPP/en_C...

This “study” is literally from an organisation dedicated to keeping freight transport on roads, it’s hardly unbiased, and is actually of very poor quality - I’d expect to see, for example, an explanation of how the routes involved were chosen for the study. Additionally, if the study said anything other than “road freight is good”, it just wouldn’t have been published by this organisation!

Here's the best source I have found for back-of-the-envelope calculations for energy use: http://www.withouthotair.com/c20/page_121.shtml Calculating emissions from energy depends on the local mix of power plants.