What I did not see in your comparison were: cost savings of not moving all of the diesel prime mover, fuel tanks, generator(alternator?) etc dead weight. You are certainly correct that the capital expense of installing the catenary and all of the substations and accessories, is huge. As to emissions,I tend to believe that it is easier to "police" emissions at large single points--generating stations--rather than multiple moving targets. And, of course, long before the current order of trainsets are worn out, we will have far more renewable electrical generation than present.