Sign says, "Street Legal Motorcycles Beyond This Point Only Vehicle Code Enforced" This road is is poor conditions but I have driven it in my Honda Civic, though I would not recommend it. While on this road a dump truck, a water truck, and a large service pickup type vehicle passed me. There are structures on the grade that need to be serviced so vehicles are necessary. Certainly a 4-wheel and bikes can go up this road (saw some bicycle riders ascending while I was there. I have seen road vehicles up here before. The terrain rating is based on the walk though by-in-large, it is not a bad hike up here. First part is the steepest.