There are plenty of Map tools worth exploring (remember Civil 3D is built on Map), this is one that I have been using a lot over the past few days. It is similar to the EXTRIM command, but it does a much more complete job and has a few more options.Â
 
When you are prepping data for Map Topologies, Civil 3D parcels, or just cleaning up a site plan, use MAPTRIM and MAPBREAK to “cookie cutter” your linework.
Hi Dana,
Just a reminder for everyone wanting to use these great tools, that they will NOT work with Civil 3D objects (unless you explode them first, and that’s EVIL). They will only work on basic AutoCAD entities.