thehpfacts:

First a reminder: It looks like Universal is building Diagon Alley in Universal Studios which is not the park that Wizarding World resides in. A Hogwarts Express will be created and connect Diagon Alley and The Wizarding World, and you’ll likely need tickets to both parks in order to have complete access.

Now the new info: Screamscape has fresh details concerning how the two lands will connect to one another…

From what I’ve been able to learn so far, which I was expecting to hear, the Hogwarts Express train ride should not be a true locomotive style train ride. There will be a locomotive and coal car, but purely for appearance’s sake, connected to a trio of passenger cars.

By design, there should be two separate train units which will load and depart their respective stations simultaneously, along a single section of track, that will split into two side by side rails only in the middle of the trip, allowing the two trains to slip past each other. The trackway between the two parks will actually be elevated up in the air the entire way, which will technically place Platform 9 ¾ on the second floor of the King’s Cross station on the London side. I’m not certain, but the raised ground elevation at Islands of Adventure may allow for the depot to appear at ground level. The elevated track system will allow for large trucks to still pass underneath along Universal’s busy back roads.

Screamscape also notes that a company called Doppelmayr may be the ones developing the train system after their experience with Ocean Park in Hong Kong:

Now, the insides of these cable cars will be an entirely different matter, and will appear more like the inside of what I believe is called a “sleeper car”. (Forgive me if I’ve used the wrong term… I’m not train person.) The interior will feature a narrow walkway down one side of the car, with individual doors leading into the separate rooms, each furnished with a pair of face-to-face seating bench seats, with a single large window (ie: video screen) to the outside world on the far wall end. This will be your window into the Wizarding World for the duration of your journey between London and Hogsmeade.