Given the higher carrying capacity per bus or train, it would certainly seem that transit could provide some environmental benefits. The problem is the gap between theoretical capacity and actual ridership. Public transit is so inconvenient and unattractive that its actual ridership falls far short of its theoretical capacity. Average load factors of 20 percent are typical.
Figure is for light rail.
Heavy rail would be 3,046 BTUs. If transit doesn't save energy, it can't make much of a contribution to the reduction of urban air pollution. While many are under the impression that urban air quality has been getting worse, objective measures show improvements over the last two decades. In terms of ambient carbon monoxide, parts per million have dropped by about 50 percent since 1975. The improvement made in air quality over the last two decades owes little to public transit.