The problem with subway systems is that they are great once they have enough reach and stops to reliably and frequently get you were you need to go without needing a car. However, a small subway system with infrequent service and only a few stops isn't all that useful. If we take the claims here at face value (not saying we should) then this is a solution that provides value immediately for people commuting by car, and if the network becomes widespread enough it becomes easier to rely on it as a pedestrian. Essentially it might be a great way to bootstrap a transition to public transport in car-centric systems.

Also note that if you get an increased amount of people commuting in these tunnels without their own cars, new public transportation built by the city becomes a lot more valuable as well, since there's already a lot of people getting around without cars.

That said it is funny how private companies seem to rediscover public transport. Looking forward to Uber Train.