Isn’t it the IRT and NRT that use different gauge of track? So, yeah; this is an expensive and unwieldy proposition assuming NOTHING went wrong (something always goes wrong).

because building that much wall for that many stations is a waste of time. Seriously, think of all the outdoor stations. We can usually take care of ourselves...

LOL - how long have you lived in New York? How much do you know about using the 4/5/6 trains at rush hour? It’s almost as if you had no idea how badly we needed a better way to shuttle 30% of the city around. But sure, let’s make this all about Brooklyn’s transportation needs, because now that you can afford a small…