nevermind, found the answer on the usmle website... in case anyone else is interested:
"Parking Near the CSEC Center
Free visitor parking is available in the west visitor lot adjacent to the building. Note: The signs in the visitor lot indicate one hour parking only. This does not apply to Step 2 CS examinees. You may leave your car there for the duration of the exam. Please do not park in spaces reserved for other tenants such as First Midwest Bank, Chicago Title, or Westwood College."