MTA's "East Side Access" website (you can Google it)shows that the plan is to build new tunneling to route the LIRR from Sunnyside, Queens into the presently unused lower level of Grand Central Terminal. In the heyday of the New York Central and New Haven RRs, this lower level was exclusively for commuter trains. Long distance trains such as the 20th Century Limited ran from the upper level, now the domain of Metro-North.

If the lower level is exclusively LIRR, then those tracks can have overrunning third rail. If there is a portion under Park Avenue where Metro-North must share tracks with LIRR, the engineers must have figured out how to accomodate both types of third rail access. According to the website, MTA is not planning any shared stops for LIRR with existing subway lines such as Lexington Avenue.

Westbound Amtrak trains from New Haven diverge from Metro-North trackage at New Rochelle to enter Penn Station. My understanding is that they are routed over Hell Gate Bridge, but someone please advise if Amtrak follows another route to Penn Sta. Southbound Empire Service departs Metro-North tracks south of Yonkers (White Plains?) and follows Amtrak's route along the west side of Manhatten into Penn Station. My earlier post was to suggest that Metro-North could easily run some trains into Penn Station by these routes, using overhead catenary for New Haven trains and underrunning third rail for Hudson Line, just as Amtrak does currently.