It's not just unpaved roads. I also find that "private" roads (inside gated communities) around me are often extremely far off in terms of speed limit. There are private roads around here with speed limits of 45+ MPH that Google seems to calculate as 15-25MPH. It really throws off the time estimates if you're coming from or going to one of those neighborhoods. And it's been like that for YEARS. If they were using user-generated data, I'd expect that it would eventually get better, but I've seen no evidence of it. Waze does a better job at this.