Fastraks = Pollution Reduction

With 3/4th of Fastracks riders being existing transit riders (that is, moving them from buses onto trains), how is this sort of pollution reduction claim possible?

http://www.denvergov.org/CouncilDistrict12/FasTracksAddressesCongestionAirQuality/tabid/383055/Default.aspx

FasTracks will make it easy for people to come into Denver for work and fun while decreasing pollution. It is estimated that FasTracks would reduce carbon dioxide pollution every year by 1.5 million pounds. We have proven in Denver that if light rail is built, it will be used. Of the three completed rail projects, all have ridership far greater than initial projections.

And to boot, what were those initial projections? My experience in Minneapolis with the Hiawatha line was that in the late 1990s when there was the initial hard push to get that LRT line built, they were using higher projection numbers than they were using in as the funding was finalized. And later when they met those first "initial" projections, they claimed it was doing better than projected when in reality they were at the level that they had first said they would be.