Hello. Welcome to Just Answer.
I see no issues with what you have proposed, relative to crossing a new underground feed over or under an existing feed.
However, I do have one suggestion for your installation.
Actually, I do see one issue with your planned URD wire.
Detached buildings require a 4 wire feed, per the NEC. Supplemental grounding via ground rods are also required. For a 200 amp service, you need 2 rods, spaced 6 feet apart.
In addition, though it's not required, I would put the wire in PVC conduit. For a trench that long, especially.
That way, if the wire ever fails (which some veteran electricians say aluminum is particularly prone to do), you simply pull it out and pull in new wire.
I didn't think I would have to run 4 wires as I am not going to power off of the Breaker panel in the house. The meter is currently on a pedistal near the street, +/- 300' from where the power enters the house. My additional run to my new building would be Tapped to the meter by the power company and the added service would have it's own panel in the new building. I just wasn't sure if crossing cables causes any problems, or if I need to keep them 6" apart or have some other type of barrier. I could run the cable to the outside of the existing cable and not have to cross it but I would be trenching into the drip line of about ten pine trees. I'm not sure if the existing feed to the house is in conduit or not, I guess I will find out if or when I hand shovel that area. The soil where I live is pretty sandy and this type of cable is what was recommended.
If you are tapping into a pedestal, that does change the type of wire you can use. Most likely, there isn't an earth ground source at the pedestal. That's a very atypical installation. Most utilities won't do an installation like that. It sounds like you will need another meter at the outbuilding. Most utilities only allow one meter per residence.
You can establish your earth safety ground at the outbuilding, with ground rods, if the URD is coming from a utility pedestal. That means you do only need 3 conductors, as suggested previously.
With the meter being at the street pedestal, as long as your new wire taps into the load lugs of the existing meter, the usage for the outbuilding will be tracked.
That means a second meter would not be necessary. Was it your utility company who said you could use 3 wire URD?
I would probably contact the local electrical inspector, just to make sure he'll sign off on it.
Before beginning the work, that is.
If you put the new feed in conduit, any concerns about distances between feeds would be unnecessary.
A side note about using conduit... you won't have to dig the trench quite as deep. Feeds in pipe only need to be 18" deep, not 24".
If you do decide to go direct burial (no pipe), when you get to the point of crossing the existing feed, I would go under it, not over it.
It was the inspector that said the URD, the power co said they can tap the load side of the meter. Sounds like this is common in this area. If I were to use the conduit I could go 18" , what size of schedule 80 conduit would I need to use? My run to the garage is just under 200'.
Let me consult my conduit sizing chart. Can you stand by?
OK, just as I suspected, it is suggesting 2" conduit. However, for a run that long, I would go up at least one size. For the minimal increase in pipe, I would go up to 3" pipe. When it comes time to pull the wire, you'll be glad you did.
There is 2 1/2" pipe available, if you only want to go up one size.
Minimal increase in price, I meant to say.