The 'parking area' could be the end of the in-process-of-being-dug return part of the loop. Once the return loop is finished, then returning empty pods could return 'slowly' if there are more pods than loading docks.
With 10 loading docks [think one air terminal with 10 airplanes with 10 moveable tunnels going from waiting area to each plane, only pairs of double doors (pod and dock airlocks) instead of moveable tunnels, gates a little more than a pod's length apart, and the whole thing automated], ten pods could be filled and sent on their way simultaneously (or nearly so), delivering 16 x 10 people in 4 minutes (or so). (With vacuums in the tunnel, the pods won't have to wait for settling air or anything other than electricity usage.) Add half a minute for loading and moving new pods into place, and you get 100 pods (up to 1,600 people) from A to B in 45 minutes. (If you only had 50 pods, then add 5 minutes or so to get all 50 back to the starting docks.) Halve the time if you have 20 loading docks.
