Roaring Camp is on private property (leased from the heirs of the man who saved the woods over 100 years ago, Joseph Welch). The RC&BT crosses no public roads, and therefore is not under FRA. The standard-gauge SC&BT, however, (if steam were to run) has grade crossings at Graham Hill Road in Felton towards Olympia, as well as Rincon, and the street-running in Santa Cruz (it's been such a long time, I can't remember). There's always been stuff flying around on getting steam on the SC&BT. If John Manley's SP Consolidation (rescued from Santa Cruz by I believe at least two RC crew members) ever steams again, I think that would probably be a nice addition; though I have no idea what his plans are for it. Since he's in the boiler business and a Form 4 is obviously having to be done anyway, would work well!
Back to narrow-gauge...the Yosemite Mtn. Sugar Pine I don't believe is under FRA (only crossing is the entry road if I remember), obviously the GLR, the privately-owned Pacific Coast being developed in California's Central Coast, probably the short 3' line in Nevada City which is rarely used. However, all of these operations have steam locomotives as it is, and are in California.
As for narrow-gauge elsewhere and grade crossings on public roads, I don't know. I'm ashamed to say that I've never visited any other 3' narrow-gauge operations outside of California, Florida, and Connecticut!
-Ed Kelley