With the low rolling resistance of a steel wheel on rail, rail transit has the potential for conserving energy. Energy will be saved IF rail transit
While all of these "ifs" should be satisfied, rail transit projects satisfy none of them. The most flagrant violation is that creating a new rail transit system encourages more travel, thereby wiping out any possible gains in energy use due to possibly higher energy efficiency.
A new rail transit system today generates additional passenger-miles of travel. The fast comfortable ride on it encourages people to use it for long trips, such as commuting to work. If it didn't exist, such trips might not be made. Also, since many of the new transit riders formerly drove, highways become less congested, enticing more autos to use highways.
How can this be avoided? There are many ways to help do this. To say that many of them are controversial is an understatement.