Owning a car in a metro area is ~$8,000/year. There's 1.3 cars/household, so we're looking at ~$10,000/year/household.
My metro area's per-household budget is ~$17,000/year. ~$4,000/year on that is spent on transportation, including public transit, roadway, and highway maintenance and construction.
Tripling the transportation budget, at the expense of personal automobiles would absolutely deliver many of those things.
NYC has a crap bus system, because they have to share roadways with automobiles, which are the cause of NYC gridlock. If buses had the right of way, they would work much better. And it doesn't take being Nostradamus to figure out at least a couple of good, new train routes - in any metro area.
I'm sure you could find me some examples of train routes that were built, and then turned out to be under-utilized... But I feel that they would be the exceptions that prove the rule. Every major metro area is seeing population growth, so it's not like people will suddenly move away from the train lines. Not to mention that every line of rail tracks has the throughput of a super-highway[1], at much smaller footprint and cost (If you take into account the full cost of vehicle ownership.)
[1] In Vancouver, any one of the three SkyTrain lines has a throughput of ~14 lanes of highway, during peak hour...