If a route doesn't have quick drives you can add your own through the build menu. There are various tutorials on You Tube showing how to do it and the process is relatively quick and easy. Adding extra moving AI traffic is more complicated. There are different ways of adding your own consists but I have found using TS Tools to be the easiest option.
A Quick Drive scenario is Unique to a Route You have to designate the start, intermediate and end locations. https://steamcommunity.com/sharedfiles/filedetails/?id=2222378782