My stoker and I spent the weekend in Milwaukee (Brookfield, actually) and rode 20+ miles on both Saturday on Sunday, primarily on local bike trails. Lots of paved trails in the area. Sunday rode to Port Washington on Lake Michigan.
Note: Found out that it is possible to average 27mpg over almost 500 miles with a tandem bike on a roof rack. Saw no other cars on our trip with a bike on the roof.