what I'd try is if it's possible to export your data either as shape file (.shp) or openstreetmap (.osm). you'll have to make sure that the width information is stored as actual attributes of the line segments. how you do this specifically in AutoCAD, sadly I don't know ..
maybe someone else knows this ?
otherwise, what you could try is exporting as dxf, 1 file for each street width. after you have imported them into the workspace and then imported into the scene, you'll have n layers. there, you can set the street widths for all elements in the layers. once this is done, merge all layers into 1 layer and run the clean graph too to merge the graphs. with graphs on different layers, blocks will not be created.
let me know if this helps.