1.Remember setting System Unit Scale to “Meters” or “Feet” in [System Unit setup],and modeling with real size.For example,if the real size of road width is 20 meters,then the amount of road width should be 20 in 3ds max,but not 20000 or other number.
2.To use TerrainAxe,convert your object to Editable poly.this is because most of the tools is for poly,and note that this tools is invalid to EditPoly modifier.
3.Remember that the farther the object is away from orign,the bigger the error become. the center of scene must not be too far away from orign,otherwise the verts position on the object is not correct,for example ,verts of splines from AutoCAD is become jagging.