So you want us all to move back into the cities? That is the only way I can see that mass transit would work on a wide scale. The automobile allowed the creation of the suburbs, now the suburbs will make it very hard to get rid of the automobile.
This solution also implies a large investment in the grid to handle vast amounts of power for mass transportation on a grid that is very close to capacity now on very hot or cold days.
Using nuclear energy to create "artificial gasoline" admittedly is not an elegant solution, but it would allow you to put a gasoline generation plant near a nuclear facility and save load on the grid. On the downside, there is zero chance a liberal will ever vote for this.
There are no easy alternatives here.
So you want us all to move back into the cities? That is the only way I can see that mass transit would work on a wide scale.
Our cities are expanding anyway.
Even suburbia is getting more crowded than ever.
Population of the United States
1930 - 122 million
1940 - 132 million
1950 - 150 million
1960 - 179 million
1970 - 203 million
1980 - 226 million
1990 - 248 million
2000 - 281 million
2010 - 309 million (estimate)