I’m not sure if there’s actually any parking for regular employees in the WTC complex. But there are a lot of underground loading docks, and parking for busses and other official vehicles.
Under the PAC will be loading docks and a spiral ramp that goes up to street level. That’s what they’re building now. I think the street-level part may be just an exit (the main entrance being under Liberty Park). The docks will be the permanent main loading docks for 1WTC, which will replace the temporary building currently extending from the east side of 1WTC.
Because the ramp goes up to street level, they won’t technically be building the PAC until well after this is above ground.