AFAICT, the majority (60%) of funding for roads doesn't come from direct user charges...
Roads are subsidized, free parking (and generally a lot of paid parking) is subsidized, and the sprawl encouraged by car dependence combined with the resulting infrastructure costs has and will continue to bankrupt cities.
I don't think we should "just only have trains", but the current US transit landscape is absurdly stupid and inefficient.
Vigorous activity is defined as something like > 75-80% max heart rate, or > 6.0 METS, not as an absolute, all out sprint. It's actually quite far from what you expect
The 2019 physical activity guidelines for Americans include consensus recommendations including the evidence and some good graphs to visualize the "bang for buck"
For those curious, those (weekly) recommendations are: twice weekly resistance training, and 150-300min moderate intensity aerobic activity, or 75-150min vigorous aerobic activity.
If you want a program to just give you a starting point, I highly recommend Barbell Medicine's (free) "Beginner Prescription"