As I've written before and other people have noted before me, Mass transit fights global warming in two ways:
1) When population density is high enough to make the use of mass transit efficient, a bus burns less gas than the cars the passengers would take if the bus were not available.
2) Mass transit encourages and enables a population density greater than would be reasonable without it. And a greater population density means a lower carbon footprint per capita.
Thus, one of the most effective things that politicians -- federal and state -- can do to reduce the carbon footprint is to encourage and subsidize mass transit where it is effective.
The problem is that it is effective in only a few areas. And, with the possible exception of New York City in its state, those areas do not have the population to have the representation to get those appropriations. So the good-government choice of encouraging mass transit where it is effective conflicts with the political choice of shipping those appropriations to my district.
That leaves us with several unpalatable options.
1) Fund mass transit where it wastes gas until most politicians get a little of the pie.
2) Leave mass transit to be funded out of passengers and local governments, which means leaving it ill-funded and underperforming.
3) Put it in a group-centered log-rolling pool: "We are all agreed, if your group votes to fund mass transit, our group will fund agricultural subsidies."
Concrete examples of # 1 after the jump
When, at one time, the federal government was funding transit in as broad a sweep as it could, Holland Michigan, which is nobody's idea of a population base to support a transit system, got a subsidy. They invented Dial a Ride. This involves calling a central location to tell them where you were and where you wanted to go. A van and driver would show up soon to take you to your destination. This differed from a taxi in three ways:
1) On the odd and unlikely chance that somebody else in your area called up at almost the same time with a destination which could be worked into yours, you had to share the ride. It must have happened, but my family's stories of Dial a Ride never involved such events.
2) The van was much larger than the average US taxicab.
3) Because of the federal subsidy, it was much cheaper.
During another of the federal government's rare excursions into subsidizing mass transit, they decreed that transit should be regional. They wouldn't fund anything local. Although the Chicago Transit Authority already serviced several close-in suburbs (and although Chicago has a larger population than several states do), that wasn't good enough. The other suburbs said to Chicago "Well, you want this subsidy, and we don't really care. We've got along without buses this long." The final deal was that the money in the fare box would be divided to Chicago's disadvantage, but there would be a Regional Transit Authority. This would get enough federal subsidy that the CTA would still get more money than it would otherwise have gotten, even though the suburban buses -- now PACE -- would get a bigger share. We still have a Regional Transit Authority. PACE still gets a more generous share. The federal operating subsidy is a faint, although fond, memory. The suburbs are now quite pleased with their service from PACE.