We started our hike at the winter trailhead and there was no sign of vehicles or vehicle tracks all the way up to the summer TH in Stevens Gulch. It would be impossible to reach the summer TH in a 4x4 because there are sections of the road where it is narrow and there is steep sloping snow. The snow on the rest of the road is icy and deep.
The snow at the summer TH is probably best tackled with snowshoes, else you will expend much more energy with each step.
The road from the summer to winter TH's is still skiiable and there were lots of ski tracks.