The THORNBROUGH Interchange demo has been around since 1981 (or earlier).
Many of the examples in the MX / MOSS manual actually refer to this design.
I would suggest you execute the example attached, and then see how the design is created via input file (by looking at the manual).
(I hope my file upload is successful - if not, ask an Administrator to e-mail thor105.inp to you).
PS Read this thread:
communities.bentley.com/.../54464
(Please visit the site to view this file)