Get over it. SMART will buy what FRA lets them buy. Whatever it is will probably have to meet heavy rail standards (read Colorado or equivalent DMUs). You still don't want to head-on with a freight train; Newton's r/w law says the passenger train always loses because the freight is bigger. But if it happens (it shouldn't but you have to allow for the Murphy factor) at a reasonably low speed it may be survivable for the majority of occupants with a Real DMU (or most commute trains in push mode, or for that matter an E-Coast EMU like on LIRR where freight & passenger DO mix it up though I don't think it's been tested in recent years thank goodness) but not in a diesel LRV. That's why FRA won't allow LRV (electric or diesel) in situations where heavy & light rail might get together.

BTW, is there anyplace other than LIRR where outside 3rd rail electrification is still used WITHOUT grade separation? Last time I was there I was amazed on the ride into NYC to go thru many grade crossings (yes, the lights and a/c drop out after a few seconds to maybe a minute depending on the equipment) on the outer 1/2 of the line. They don't go to full grade separation until nearly in Queens, and the r/w fences aren't in the best of shape in places (sometimes just rusting barbed wire). Reminded me of some of the pictures of Marin NWP electrics but with stainless steel cars. You probably want to be careful when doing industrial switching (with diesels - forget which shortline has the contract) in electric territory.