One would think that with Tier 4 being in place for, what, almost 10 years now for trucks that the basics would be worked out and routine. For light duty diesels (VW notwithstanding, which resembled your description of International's efforts), DEF has been around for a long time and works fine - just refill the tank at each oil change. It's also a mature technology for stationary engines like backup generators.

I can understand the Class 1's not wanting DEF. At best, it's inconvenient to have to use it, and at worst it's a hazmat problem if they would have to do unscheduled refills outside of servicing facilities. GE (WABTEC now) addressed that problem by doing Tier 4 without it, at a cost in complexity and fuel economy; presumably EMD has done the same now. The commuter lines service their fleets at a central location mostly daily anyway, so DEF-based Tier 4 is OK for them and keeps fuel economy in the Tier 3 range; plus, being govt agencies, there's more emphasis on clean (public relations & environmental impact) than on minimum cost. Will be interesting to see how Amtrak deals with the DEF issue in long-distance use of their new Chargers.