Multiple trains on one track.

Using 2 PS2 or PS3 engines in DCS Command control (TIU & Remote), it is simple to run 2 trains on the same track.

Mixing with standard trains is more difficult but has been done with limited success.

To do so you must have a heavy enough load on the conventional engine to slow it below the speed the DCS engine & train can run with the applied voltage on the track.

It is far simpler to run a pair of trains under DCS and keep a separate loop for a single conventional train.

DCS allows this easily on any track as you have 2 Variable channels controlled by the remote. They vary the voltage on the rails to control the older engines. AND you can switch the loop to full command control simply by pressing a button.

This lets you run any train on any combo of 2 loops.

I do it regularly.

BUT: I suspect you will find as I did that you run the older trains less and less over time and run the Command control equipment more.

The newer ones have incredible sounds and capabilities the older ones cannot match. Like backing a train onto a siding anywhere and disconnecting the engine by remote control to go pull a different train. No Uncoupling track section needed !!!

If you want uncoupler sections for your older trains they too can be under command control by connecting up an AIU to DCS. Each AIU can control 10 switches and 10 single action accessories. And you can daisy chain up to 5 AIU's per TIU.

I am up to 2 AIU's now just for switches.

Want to know all there is to know about DCS ? Buy Barry's book "The DCS Companion" thru the MTH website. Best train money I ever spent.

There is new equipment out there that I do not have nor can ill afford to use, that will let you do just about anything with a varying number of trains. for this you will have to get your answer from someone more experienced. However for your older equipment you can run several trains using what they call a block system. In a block system different sections of rail are electronically isolated from one another, this occurs when the power to the center rail is disrupted by an insulated section or material, and then electronic switches ( not to be confused with rr track switches) are installed to turn on or off different sections of track. I am sure there are many places to reference this, but Lionel explains it pretty well in their "big book of Lionel" in chapter 7 entitled two train operations.

Remember the old conventional engines are controlled by varying the track voltage (using the transformer throttle).  The new DCS engines use constant voltage and you set the speed through digital commands. 

Besides Barry's Book OGR also has a DVD that explains DCS starting with the basics.

Also review the DCS forum on this site for more info!  And you can also control Lionel TMCC engines through DCS with some additional equipment. 

Also you could always convert your old engine to Command and Control with the installation of the correct board.  At the present time these boards are only available for Lionel TMCC but it is an option than you don't have to worry about it anymore.