Difficult to implement any kind of useful public transit that would obviate the need to drive everywhere.
For almost 40 years Portland Oregon has been developing light rail all over the metro region. Rail has been extended to the major districts within a 10 to 15 mile radius of downtown. (Which is a good share of the "spread" that the regional urban growth boundary allows.)
MAX and street-car lines are heavily used but there are still many cars and traffic can be terrible. So I guess light rail/public transit are never the whole solution by themselves. Then again, what single modality is ever the "magic bullet" answer to enormously complex problems?
Portland Oregon is a vary low population city .6M in the middle of no where. It would have been fine without any form of public transit. The real issues show up at around 10x the population where sprawl is to low density to support office buildings and people at the edge can't reasonably commute to the center of the city even with public transport.
You don't need to be NY for transit to make a huge difference. Portland is a squarely mid-size American city and its quality transit is a key selling point.
Any way. Nominally DC has a population of 646,449, however the DC metro area is 5.8 million. The Baltimore Metropolitan Area has grown steadily to approximately 2.7 million and has fewer issues with transit, but it's getting steadily worse.
And the NY metro area is 23.5 Million people.