I doubt steepness (or traction) currently is the issue (no snow or ice, from the report you got). For us, the concern was rocks/obstacles in the road, and pits/gullies, particularly at one turn. It is a dirt jeep road that sees some big weather. So what is nice to have is clearance (more than 4wd) once the snow clears.
We did it in a Volvo station wagon, slowly and carefully, in August 2010. We also saw everything from Honda Civics to true SUVs (it was open house at the lab).
My understanding, which could be faulty, is that the lab (rather than the county) maintains the road and that maintenance/regrading is required from time to time, particularly after the winter. So the fact that the road was relatively driveable in a sedan in August 2010, for example, does not mean it is as drivable now. That is why it is probably best to check with the lab.
Btw, while we drove this road in a station wagon, we kind of wished we had more clearance in a few places, as the drive would have been easier. We got through, as did all the other vehicles we saw, but still.
