Is the direct service from Baltimore airport to Washington DC free and where does it stop in DC ? If return flight from Washington DC is Baltimore Airport where do you access direct train service?

From my Understanding it's called Baltimore-Washington International airport because of the vicinity it's in...the airport is actually located in Glen Burnie Maryland

Not sure what you mean by direct service. But you can take a bus from the Airport to the BWI train station. From there a train to Union Station.

Good question.