Actually there were two of them:

This one-of-a-kind, near-G-scale trolley was made by Bill Ferguson in Toronto, Canada, in 1967.

That’s the one you see Mr. Rogers interacting with in his home.

The missing ingredient in the HO neighborhood with all the houses and trees was an HO scale trolley.

So they built a smaller one, which you see at the beginning and end of each show.