Oldcat:
First, I think you meant 16" rather than 18" as 16" and 21" are the only diameters that have been produced by Kline, Lionel or Bachmann.
And yes, those 16" curves were made to "nest" inside the 21" diameter curves without any overlap or space between them. However, you have to be careful what you run as some vehicles will overhang on the inner curves and sideswipe a vehicle on the outer curve when they are both in the curves at the same time. If you are only running short automobiles it may not be a problem but if you wanted to run trolleys or tractor trailers you will have problem.
The next issue is you will need more than 21" of table width as a 21" 'Streets circle measures 21½" in diameter from outside-edge to outside-edge.
When you buy your track make sure to buy enough "curve-to-straight" sections. These are the 2½" long straight transition sections which are needed when connecting a straight section of track to a curved section. The grooves on the curve-to-straight sections taper down from the wide groove of the adjoining curve section to the narrow groove of the adjoining straight section. You will need one such section at each end of a transition from curved to straight otherwise your vehicle will derail.
Lee Willis, who used to post on here, wrote two eBooks on using super/e-z streets several years ago. You might check the archives as he had made them available for downloading by OGR members.
HTH,
Bill
