We don't really want the trains (because of the way the US developed its cities). Let me give an example. In order to add a few more daily routes from Chicago to Milwaukee on Amtrak, a freight train would have to hold on a holding line for several hours in residential areas to let the Amtrak through. The increase in ridership, not just riders shifting their schedules, would have been at most a few hundred.
So in order to get a few hundred cars off the road, Amtrak would have to build a holding track (carbon cost), add more rolling stock to the route, burn more diesel, and a residential neighborhood full of children would have had diesel trains idling for hours a day.
The total economic and environmental value of the program was negative by most measures.
This seems poorly argued to me. You're making a number of assumptions here which I don't see why they would hold:
1. Amtrak ridership will barely grow, at most by a few hundred riders per day. If you're this bearish on trains then naturally you'll think nobody wants to take the train and you don't think Amtrak should build more trains. You're coming into this assuming that nobody wants to ride the train.
2. Building dedicated track between Chicago and Milwaukee would be cost prohibitive for Amtrak or otherwise infeasible. The majority of the cost for building track comes from acquiring ROW (so purchasing the land), grade separations, and utility relocations needed for laying the track. Chicago to Milwaukee in particular is one of the cases where these costs are probably _lowest_ as much of the ROW is cheap to acquire (outside of the direct Chicagoland area), the land is fairly flat so grade separations are rarely needed and utility relocations are cheap to build.
3. The opportunity cost in carbon for added vehicles on the road would somehow be less than the opportunity cost for rolling stock to idle. Even if freight rail continues to refuse to electrify in perpetuity, the added carbon from private vehicle emissions will quickly dwarf extra carbon emissions from idling freight cars.
I think you're coming at this from a "trains are stupid, here's why" perspective rather than an unbiased cost and carbon perspective. These arguments change in areas where ROW acquisition is expensive or grade separations and utility relocations are difficult, but Chicago to Milwaukee has very few of these problems. In particular the problem in this part of the US is that while rail works to move from city-to-city, most Midwestern cities (other than Chicago) have no actual transit to speak of. Once the Amtrak drops you into Milwaukee, if there's nowhere to go via train, then you're stuck, in which case you may as well drive the whole way. That goes back to the fact that rail/transit in the US has been historically and systematically underfunded, particularly so in the Midwest where Detroit had a lot of negotiation (read: money) leverage in the golden years for American auto companies.
This to me just argues for separate lines for passenger vs freight trains.
Especially if we are talking about installing high speed lines anyways, doesn't make sense to turn a freight line into a high speed line and then share it (other than the fact that you wouldn't need to eminent domain as much).
So in order to get a few hundred cars off the road, Amtrak would have to build a holding track (carbon cost), add more rolling stock to the route, burn more diesel, and a residential neighborhood full of children would have had diesel trains idling for hours a day.
The total economic and environmental value of the program was negative by most measures.