advanced rendering for AutoCAD
You can send the model using the Support->Upload a File option above-- this is your best bet. Include instructions for how to reproduce the problem (for example, which view to render.)
If you can't do that, keep in mind that it's almost impossible to answer this intelligently without more information. A picture of what you're getting would probably help.
Just got the model. It's really having fits rendering the roadbed-- AutoCAD is generating lots of really long, skinny triangles. When I erase the road things go much faster. Not sure what to do about this one-- it's a good application for Rhino (you'll get a much better mesh automatically.)
Some other items which will improve things (probably not enough without solving the roadbed problem, though):
- Don't use displacement maps for faraway stuff. Definitely not worth it for the grass in this model.
- Avoid Exterior mode indirect lighting-- use the Path Tracer or Hybrid engines instead.
- Avoid super-high resolutions, the extra processing time is almost never worth it. Up-sample in Photoshop if you must.