Getting the roads and cars is easy. Select all your streets and apply the "modern streets" rules from the "rules folder in the Modern streets example. Then go through and set the correct start rules (sidewalk, street, criossing, etc.) and generate. Depending on the size of city, t might be easier to select "by start rule" and replace the rule file for each group.  I have done it a few times, it works quite well. Don't forget to set "highLOD", otherwise the cars and people, etc will not show up.

The billboards are more complicated because they are a sub rule. I'll have a look and see if I can come up with a simple setup that I can post here.

Ciao

TD