Using a 90 degree crossover

Look at the underside of the crossover.  The center rails should have a metal strip connecting one another across the middle of the crossover.  If that is the case, there should be two strips of metal.  These strips carry power across the plastic part of the crossover.  You should be able to slip[ a piece of cardboard, like the type found on tablet backs, in-between the two strips.  The outer rails will not matter because they are connected to the common terminal of your transformer.  Or the should be.  

As for me I need some clarification. It seems you want to connect one loop to another loop with a 90 degree crossover. If that is the case, I believe an insulating pin in the center rail on the exiting track to loop with trolley will work fine. (I assume you are running conventional)

You will experience a concern when trying to re-enter back through the crossover. The power will be different. (One of the many reasons I like Command Control)

What kind of track?

I wonder if this is possible with conventional, without setting up a block, which would stop trains from one direction to permit opposing to pass?  Now with command control, is it not possible to have a collision at the crossing, with both trains running?

You won't need to use insulating pins.  If the crossover is made the way I explained in my initial post, once you isolate the two metal strips on it's underside, then each track will be electrically isolated from one another.  

I don't know which transformer you are using to power your layout.  You mentioned that the trolley and the main line are powered from two separate terminals.  So as I mentioned in my initial post, be sure that those two terminals are powering the center rails.  The common terminal should be connected to the outer rails which need not be isolated from one another.  

The result will allow you to power the trolley and the main line individually without fear of short circuits.  

I hope this helps.   

With both loops running off the same transformer or two phased transformers, it will work.  The center rails will be powered through the track pins.  The square in the middle is dead.

The trolley may have to be running fast to get over that square dead spot.

Look at the underside of the crossover.  The center rails should have a metal strip connecting one another across the middle of the crossover.  If that is the case, there should be two strips of metal.  These strips carry power across the plastic part of the crossover

The Lionel crossovers with which I am familiar use one piece of metal to connect all four center rails. When I wanted to isolate the two lines, I removed the piece of metal, and attached jumper wires.

I

ADCX Rob posted:

What kind of track?

he edited his OP... PW tubular O

colorado hirailer posted:

I wonder if this is possible with conventional, without setting up a block, which would stop trains from one direction to permit opposing to pass?  Now with command control, is it not possible to have a collision at the crossing, with both trains running?

Collision avoidance is another issue - it is done with relays controlling the center rail power of the approaching tracks and isolated outside rails to trigger the relays. There are some optical triggers (sensors) available, also.

I know how to insulate a traditional Lionel O gauge tinplate crossover, but I am building a layout with Atlas O Gauge track and have two crossovers that have separate loops running through them and the power from one loop is leaking into the other.  There are switches connecting the two loops but they are insulated with the plastic clear rail joiners

@Miles W. Rich posted:

I know how to insulate a traditional Lionel O gauge tinplate crossover, but I am building a layout with Atlas O Gauge track and have two crossovers that have separate loops running through them and the power from one loop is leaking into the other.  There are switches connecting the two loops but they are insulated with the plastic clear rail joiners

Look at the underside of the crossover. Determine if there is a metal plate connecting the center rails in the center of cross area. You have to isolate one route from the other route. (ie. east and west from north and south) I don't have Atlas. A photo of the bottom would help.