I have two separate N scale train sets.  Both use EZ track and have identical power pack speed controllers.  I'm thinking about combining the two sets into a single larger layout and run both trains [Empire Builder] and [I forget] on the same large layout.
Question:  can I use two rerailer/power packs/speed controllers on a single large layout?  How do I adjust the speed of the two trains so one doesn't overtake the other?
You can see I'm a rookie at this hobby.

Any help would be greatly appreciated.   Thanks,