Make the glass 1 - 2 planes, if possible. Try to remove triangulation.
Also, make sure your windows are part of a separate object (not connected to the vehicle). To do this, select the window faces, hit "p", and select the separate into new object option (not sure if that last step is needed).
Also, make sure your normals are all facing the same way and that you didn't scale in object mode (or the exporter, as I've heard that messes up lighting as well).