Your comment about EPA got me speculating about another reason for this. GE/WABTEC and Progress/EMD haven't been building Tier 4 locomotives much, despite the requirement for them having been in effect for several years. Nobody wants them, really; while they work, they're expensive and require new types of maintenance (even if, like GE/WABTEC, they don't require Diesel Exhaust Fluid), and less fuel-efficient than the Tier 3s. Some Tier 3s were actually Tier 3+ (a little better emissions, but not Tier 4), some Tier 3s were placed in service before they were required to be, and some rebuilds have upgraded older Tier 0-2 to Tier 2 or 3, so the locomotive makers racked up (and perhaps purchased, from Tesla and other generating them) emission credits. They've been burning those credits every since, delivering mostly Tier 3s either new or rebuilt. So: if they deliver 2 Tier 3s and a battery model, do the total emissions add up to 3 Tier 4s? Might be some complicated math in there - do we need an accountant to properly cook the books?