Dear future elbows and anyone else who might be interested,
Just take Shady Grove, Snouffer School Road, and Wightman Road. Stay on the south side of Shady Grove so that you can turn onto Redland Extension Trail without having to cross Shady Grove where there is no light. (You will have to ride on the sidewalk when going to the metro.) More of a straight shot and the roads are better than the route google recommended. Some fast moving traffic and narrow roads but no rude behavior from drivers. And if you can ignore the carpet of invasive stiltgrass, the woods were kind of fun.
I saw a total of 1 bicyclist in the 8 hours I spent in Montgomery County on a pleasant Sunday.