You might try printing out some street drains and man hole covers.
You can either take a photo of the real ones or look for on line editions you can copy.
Scale to correct size print on your printer and use thin double sided tape to hold them on.
They really add that finished touch to the streets.
I've made a jig to drill out and shape actual holes for curb drains - I do it after the streets are done and the filler and paint hardened, because I wait until they are done and the crosswalks in, etc., to decide where they will look best. I have all the small plastic manholes covers that came with the Super-EXStreets roadtrack and will just use them, painted rust color - they are smaller than scale - about only 18" wide, but they fit the holes where the screws go .
