Subway switch-tracks: what makes the switch?

The N train runs on the local track at 42nd St. and above, and on the
express track at 34th St. and below. When it switches tracks, does a track
section move like on a traditional railroad, or is there a mechanism under
(and attached to) the train itself that chooses whether or not to switch
tracks?

Thanks to all who responded... that's what I was looking for.

-jake

"JBW" <reply@group.com> wrote in message
news:Jb6dnUQjBonsBWbenZ2dnUVZ_vydnZ2d@giganews.com ...
> The N train runs on the local track at 42nd St. and above, and on the
> express track at 34th St. and below. When it switches tracks, does a
> track section move like on a traditional railroad, or is there a mechanism
> under (and attached to) the train itself that chooses whether or not to
> switch tracks?
>