Do you mean cargo and passenger on the same track?

I have just pushed a change that will allow this - there is a new small button that allows you to select various overrides in the train panel. Allowing this for the cargo routes should be fine, they will just share the tracks as normal. (Note that only double tracks are considered where routes do not share a station). Enabling it for the passenger routes may have unexpected results because the logic was written assuming trains always terminate at stations, so bear in mind if you want to have a play :)