From New York City
Take route 78 west to  route 24 west  and exit marked as
Millburn - Springfield - Summit

Summit Ave takes you there, just follow
 the 'H' hospital signs.

Coming out of New York City there is a sludge of combined and splitting roads. One easy way is to just get on 78 west. For some of you, you won't see the choice, so Turnpike south is used to get to 78 west.

Once on 78 west, there are several choices. Getting onto route 24 west from 78 west feels like doing nothing. It feels more like a turn to stay on 78. You may get confused as 78 seems to head off somewhere else. Let it. You wind up on 24W without really slowing or making any overt turns.

Of the several choices to Summit and specifically Overlook Hospital, the Summit Ave turn is not the first but is by far the easiest.