I've been told time and time again that they weren't, that they could only be grandfathered on the same route as used before. So I am of the belief that they are not legal. However they are in use...

I don't recall seeing any FRA waiver posted in the Federal Register.

So if they are legal, somehow TriMet is dodging the question as to why it didn't buy RDCs in the first place, when TriMet could have had their hands on at least seven RDCs already in the state of Oregon (which is exactly seven more than ever operated in the RDCs' heyday), three of which owned by ODOT at the time (now owned by the Wallowa-Union Railroad Authority and once again for sale) which also owns the WES right-of-way south of Tigard (and continuing all the way to Quinaby). At least the three ODOT units could have been purchased for $250,000; instead TriMet spent over $10 million, PLUS took over Colorado Railcar and was effectively running the company for several months in order to deliver its last two cars, plus one car each for the Alaska Railroad and South Florida RTA, after which the company died and was liquidated.

Plus the Port of Tillamook Bay, which was a recipient of ODOT funds when it purchased SP's Tillamook Branch, has two more RDCs; the Pacific Northwest Chapter NRHS owns two RDC-9s that are rusting away behind warehouses in Tigard, not much more than a stone's throw away from the WES route. So today there are NINE RDCs in Oregon, when the first known use of the RDC in Oregon was on the Oregon, Pacific & Eastern Railway in the 1970s (the former SP #10, now sitting derelict in Galveston, Texas suffering from hurricane/flood damage). Although I have seen a picture of two Western Pacific RDCs passing through Union Station en route to their new owners, the Northern Pacific.

I will say that right before the RDCs came into operation I noticed a couple of brand new main track derails installed in Beaverton and Wilsonville...so maybe if the RDC is in use, those derails have to be opened up which would then comply (except for the mixed operation of the RDC and the DMUs) with FRA regulations?