There's zero reason to say that a ring line must through low density areas. You can place the ring (or partial ring) underground at a variety of locations that

There's zero reason to say that a ring line must through low density areas. You can place the ring (or partial ring) underground at a variety of locations that would be higher density, you could have it be further out from downtown as a mix of above and below ground, it's just about what we are willing to pay. Obviously, an all-above-ground follows-the-beltway route would be pretty low density. As you know, the DC Metro has several U shaped lines. It takes a ridiculously long time to get from say, College Park to Dupont Circle. Or from the stadium to Silver Spring. A few linker lines would make the downtown system far quicker internally and also accelerate those kinds of trips, even if it doesn't create a full ring. The goal should be much like the NY system: I can get anywhere in DC relatively easily using only the Metro. I think the way you've phrased the cost-benefit is exceedingly narrow. Operating a train is a fixed cost, if it's highly utilized the cost goes down. As such, making the service more useful can shift the cost-benefit. Also, there are benefits (for example fewer cars on the road) which don't seem to be taken into account. Finally a key assumption here is that Uber's price is real. I personally don't think Uber's current prices are sustainable. They are either 1.) subsidized by investor capital or 2.) dependent on paying drivers essentially minimum wage (maybe even less) or 3.) both. If you didn't have Uber around would your analysis shift? (genuine question) In the past I doubt we'd have said, "Taxis are a replacement for public transit." We should be careful of making a similar argument today. Re. low wage workers, it's a concern. You make some good points, but I'm not sure I buy that the answer is Uber or leasing EVs. How many have access to a charger for that EV? How many can get a driver's license? The poor often live precariously, they may not be able to park that car a month or two from now, or who knows what other problems might come up. In short, I think focusing on top line cost-per-ride is a very incomplete way to look at infrastructure. p.s. $40 from downtown DC to Annapolis, wow Uber is cheaper out there than here in the bay area.