At Liberty and West, the signs say "WTC authorized vehicles only." The garage access is behind the security check points, and there does not seem to be general public access. 
And then, are you talking about way 891074598 of W B'way. There is no public access to s/b W B'way south of Barclay. There is a garage exit (way 1124499552). I don't know if the garage is public since it's a federal building, but access on way 1124499552 to the intersection of W B'way and Barclay is not restricted. 