I love that you used a block representative of his name-Clays Choice! My first thought since you mentioned "
make sashing that would resemble intersections of roads" was to quilt white or yellow center lines like in a road way( you could also use some fabric paint and a foam brush to paint the strips and quilt on each side of them). Then reading through the posts I also like the idea of quilting road sign and stop sign shapes in the intersections.
Maybe also quilting a few car shapes along some of the road. If you like the suggestion of the clay's blocks looking like propellers you could do some cloud shapes in some areas of the blocks. Also like the other suggestions for the alternate blocks-echo or crosshatching.
I'm sure everyone is right He will LOVE it because it is for him from you. 