I don't think gmaps actually does that. We have a 20 meter stretch of road near our house that connects two other roads. Google, for at least the last five years, has refused to believe that this road can be traveled, having everyone take a detour. Hundreds of cars are taking this non-existing road every day, but Google still hasn't taken the hint. (Probably preventing quite a bit of through-traffic in our neighborhood, so we're actually rather happy about this. :-))