Herman,
If I understand correctly, you mask the window of the upper (street view) track to see inside. The track below must have motion too to make it look like you are passing.
To do this the right way you will need 3D motion. You will have to change the z-axis for the lower track and put the motion on a parent I am not very skilled at this, but John Rofrano is. He will probably jump in and help you out.
http://www.narrowroadmedia.com