Fastracks : More Pollution?

As expected, the FasTracks line from Denver to Boulder to Longmont, the Northwest Rail Corridor, will be using diesel to power it's trains. In a way I'm amazed that it's taken this long to officially declare it to be the case. It's simply not safe to run light rail trains with freight and would be very expensive to set up the LRT well enough so that would not be an issue. The question is, with these trains powered by diesel will they be producing more pollution than if it's riders were in buses? Their own cars?